2. Size clines were investigated in two socially polymorphic sweat bees (Halictidae): transitions between solitary and social nesting occur along gradients of increasing season length, characterised by the absence or presence of workers and offspring that are individually mass provisioned by adults. How the body size changes with season length was examined, and whether transitions in social phenotype generate saw-tooth size clines. We measured Lasioglossum calceatum and Halictus rubicundus nest foundresses originating from more than 1000 km of latitude, encompassing the transition between social and solitary nesting.

3. Using satellite-collected temperature data to estimate season length, it was shown that both species were largest where the season was longest. Body size increased linearly with season length in L. calceatum and non-linearly in H. rubicundus but the existence of saw-tooth clines was not supported.

4. The present results suggest that because the amount of food consumed by offspring during development is determined by adults, environmental and social influences on the provisioning strategies of adult bees may be more important factors than available feeding time in determining offspring body size in socially polymorphic sweat bees.

• No evidence was found that transitioning from social to solitary behaviour along a season length gradient generates saw-tooth clines in two socially polymorphic sweat bees.
• Both species exhibited converse Bergman size clines; individuals were smaller where the season was shorter.
• Despite exhibiting broadly similar patterns, size increased with season length linearly in Lasioglossum calceatum but non-linearly in Halictus rubicundus.

2. The aim of the present study was to investigate how a natural community of arbuscular mycorrhizal fungi affects the growth of the perennial herb Plantago lanceolata L. (Plantaginaceae), as well as its interaction with the Glanville fritillary butterfly [Melitaea cinxia L. (Nymphalidae)]. For this, a multifactorial experiment was conducted using plant lines originating from multiple plant populations in the Åland Islands, Finland, grown either with or without mycorrhizal fungi. For a subset of plant lines, the impact of mycorrhizal inoculation, plant line, and larval family on the performance of M. cinxia larvae were tested.

3. Arbuscular mycorrhizal inoculation did not have a consistently positive or negative impact on plant growth or herbivore performance. Instead, plant genetic variation mediated the impact of arbuscular mycorrhizal fungi on plant growth, and both plant genetic variation and herbivore genetic variation mediated the response of the herbivore. For both the plant and insect, the impact of the arbuscular mycorrhizal community ranged from mutualistic to antagonistic. Overall, the present findings illustrate that genetic variation in response to mycorrhizal fungi may play a key role in the ecology and evolution of plant–insect interactions.

• AM fungal inoculation did not have a consistently positive or negative impact on plant growth or herbivore performance.
• Instead, plant lines and larval families responded differently to AM fungal inoculation.
• This indicates that genetic variation in response to AM fungi may play an important role in the ecology and evolution of plant–insect interactions.

2. An infrared thermography protocol was used, consisting of three assays: start of activity, cold response, and heat response. Individuals of 12 populations were studied and the comparative explanatory capacities of several environmental factors in relation to the observed inter-population differences were examined.

3. The heating rate from chill coma to the beginning of activity was the variable with the highest discrimination power among the studied populations, accounting for 94% of the observed variance. Regarding the heat response, only six of the 16 thermal variables reached significance (inter-population differences accounted for 52–74% in these six thermal parameters).

4. From the three considered environmental factors (Mediterranean climate, land cover, and trophic characteristics) only land cover characteristics remain statistically significant, affecting the cold response of individuals.

5. Thorectes lusitanicus is a species characterised by a high diversity of thermotolerance and recovery traits across populations with a low degree of association with broad environmental factors. Finally, it is suggested that the apterous character of this species could be a determinant factor explaining the high diversity of ecophysiological traits related to thermal stress tolerance and the recovery time.

• Population differences in physiological responses are examined in an endemic Iberian dung beetle species (Thorectes lusitanicus) using infrared thermography.
• The heating rate between the temperatures of chill coma and the start of activity, a variable associated with land cover characteristics, is the parameter that allows discrimination among populations.
• Thorectes lusitanicus is a species characterised by a high thermotolerance, and its apterism could explain the high diversity of ecophysiological responses found.

2. This study examined whether the presence of the soybean cyst root nematode Heterodera glycines influences the performance of the above-ground leaf-chewing tobacco cutworm Spodoptera litura on soybeans, Glycine max, and whether this in turn affects the success of its parasitoid, Meteorus pulchricornis. Using three soybean cultivars that varied in the level of constitutive resistance to the tobacco cutworm, the study determined whether feeding by the nematode altered the developmental and reproductive performances of the caterpillar and its parasitoid.

3. Root feeding by the nematode slowed tobacco cutworm larval development time and reduced adult body weight. Root feeding by the nematode also had a negative effect on the caterpillar's parasitoid, by prolonging development time, decreasing adult body size and reducing fecundity. These effects increased in a linear trend and varied in magnitude depending on levels of soybean constitutive resistance.

4. These findings demonstrate that root feeding by the nematode can prime soybean plants with negative impacts on their herbivore and its parasitoid, and that the impact may vary in magnitude depending on levels of soybean constitutive defence. The results emphasise the need to integrate soybean constitutive and root nematode-induced defences for a better understanding of below- and above-ground organism interactions, and to allow insights to be gained into the improvement of soybean integrated pest management programmes.

• Root feeding by soybean cyst nematodes not only impairs tobacco cutworm development, but also has a negative effect on the development and reproduction of its parasitoid.
• These effects increase in a linear trend yet vary in magnitude across soybean cultivars expressing three different levels of constitutive resistance.
• Soybean constitutive and nematode root feeding-induced defences can have a combined effect to compromise the life-history traits of above-ground leaf-feeding caterpillars.

2. Incipient colonies of the subterranean termite Coptotermes gestroi (Wasmann) were investigated to determine if this transition was irreversible and if the burden of brood care on the first alloparents could be measured. To do so, the initial size of the work force necessary for an incipient colony to survive once the brood care became alloparental was determined.

3. The results of the study show that within 5 months after foundation, brood care duties were fully transferred to workers and the primary reproductives became irreversibly dependent on these workers for survival, reproduction, and colony growth.

4. Once the brood care became strictly alloparental, the presence of a single worker was enough to maintain the survival of the king and queen, confirming that ‘reversed parental care’ was also achieved. However, major brood loss and suppressed egg-laying activity from the queen was observed, suggesting that the burden of brood care was too high for a single worker to absorb. Therefore, once brood care has shifted to alloparents, a critical number of workers is necessary to prevent brood loss and initiate colony growth.

5. As the initial cost of brood care is rapidly absorbed with colony growth in termites, the performance in brood care of the first few alloparents in a subsocial wood roach ancestor may have contributed to the emergence of eusociality in this clade.

• In incipient termite colonies, biparental brood care rapidly shifts towards alloparental brood care. This transition may recapitulate the evolutionary trajectory from subsocial wood roach ancestors to eusociality in termites.
• Within 5 months after foundation, brood care duties were fully transferred to workers and the primary reproductives became irreversibly dependent on these workers for survival, reproduction, and colony growth.
• Once brood care has shifted to alloparents, a critical number of workers is necessary to prevent brood loss and initiate colony growth.

1. The response of a phytopathogen vector to pathogen-induced plant volatiles was investigated, as well as the response of the phytopathogen vector's parasitoid to herbivore-induced plant volatiles released from plants with and without drought stress.

2. These experiments were performed with Asian citrus psyllid (Diaphorina citri), vector of the plant pathogen Candidatus Liberibacter asiaticus (CLas) and its parasitoid Tamarixia radiata as models. Candidatus Liberibacter asiaticus is the presumed causal pathogen of huanglongbing (HLB), also called citrus greening disease.

3. Diaphorina citri vectors were attracted to headspace volatiles of CLas-infected citrus plants at 95% of their water-holding capacity (WHC); such attraction to infected plants was much lower under drought stress. Attraction of the vector to infected and non-stressed plants was correlated with greater release of methyl salicylate (MeSA) as compared with uninfected and non-stressed control citrus plants. Drought stress decreased MeSA release from CLas-infected plants as compared with non-stressed and infected plants.

4. Similarly, T. radiata was attracted to headspace volatiles released from D. citri-infested citrus plants at 95% of their WHC. However, wasps did not show preference between headspace volatiles of psyllid-infested and uninfested plants when they were at 35% WHC, suggesting that herbivore-induced defences did not activate to recruit this natural enemy under drought stress.

5. Our results demonstrate that herbivore- and pathogen-induced responses are environmentally dependent and do not occur systematically following damage. Drought stress affected both pathogen- and herbivore-induced plant volatile release, resulting in concomitant decreases in behavioural response of both the pathogen's vector and the vector's primary parasitoid.

• The Asian citrus psyllid (ACP) is the vector of the pathogen that causes citrus greening (HLB), the most destructive disease for citrus worldwide.
• Asian citrus psyllid is attracted to citrus infected with the HLB pathogen under optimal watering conditions. However, under drought stress ACP is not attracted to infected plants, and pathogen-induced volatiles are reduced.
• The parasitoid Tamarixia radiata is attracted to ACP-infested plants under optimal watering conditions but not under drought stress.

2. Data on the abundance of adult and immature stages in the Maghreb in 2014–2016 are used to test several hypotheses regarding the autumn migration of this species.

3. A strong seasonal migratory strategy was confirmed by the all but total absence of the species in NW Africa at the end of summer and the arrival of huge numbers migrants in October and November. Migration was timed to coincide with an increase in host plant availability but not with any increase in nectar sources.

4. Flower abundance was the main predictor of adult abundance in autumn, with Ditrichia viscosa, Verbesina encelioides, and Medicago sativa being key resources that attracted enormous numbers of butterflies to oases, ruderal habitats, and oueds. The distribution of immature stages was strongly predicted by host plant abundance (with traditional agriculture representing the most important breeding habitat) and latitude (most breeding occurred in the south of the region). Also, both adults and immature stages were more common inland than in coastal areas.

5. Changes in age structure of the adult population were also noted. The number of fresh adults slowly increased, indicating that butterflies did not return in a single wave and that the first offspring of the first returners were already emerging when some butterflies were still arriving.

• Vanessa cardui shows a strong seasonal migratory strategy in northwest Africa, being practically absent at the end of summer but migrating in huge numbers into the region in October and November.
• Migration was timed to coincide with an increase in resource availability. Upon their arrival, adults concentrated in habitats rich in nectar sources, such as traditional agriculture and ruderal areas, and oueds.
• The main breeding habitats were located in agricultural and ruderal areas in the south of the region, where local populations began to emerge towards the end of the migratory period.

2. In a field experiment, the influence of plant cover on the settlement of nest sites and per-capita productivity of sexual individuals by the ant Temnothorax crassispinus was analysed. In July 2014, in five areas with patches of alien balsam Impatiens parviflora, and another five of native balsam I. noli-tangere, transects composed of artificial nests were established; the nest sites were situated inside patches of balsams, and outside of them. Four hundred and forty artificial nests were used. One year later, the nests were collected.

3. Colonies of the ants three times more often inhabited nest sites outside the patches of both balsams. Besides, colonies with queens were more frequently found in nest sites located away from balsams. The per-capita productivity of sexual individuals was higher in nests collected in patches of balsam, and the colonies from patches of alien balsam produced a more female-biased sex ratio.

4. In terms of the impact on the ant, no clear differences were found between the alien balsam and the native one. The most important factor affecting the fitness of ants in areas dominated by balsams is the presence of herbaceous plant cover rather than whether the plant is alien or native.

• The influence of plant cover on the cavity-nesting ant Temnothorax crassispinus was analysed.
• Nest sites localised in balsam stands have a lower value for ants, and ant colonies adjust their reproductive effort with respect to the vegetation cover.
• Patches of native and invasive balsams equally affect the ant colonies.

2. However, previous work has been challenged, because supposedly single species have been discovered to be a number of cryptic species. Consequently, new studies are required to determine population structure and reproductive decisions of individuals unambiguously assigned to species.

3. Microsatellites were used to determine species identity and reproductive patterns in three non-pollinating Sycoscapter species associated with the same fig species. Foundress number was typically one to five and most figs contained more than one Sycoscapter species. Foundresses produced very small clutches of about one to four offspring, but one foundress may lay eggs in several figs.

4. Overall, the data were a poor match to theoretical predictions of solitary male clutches and gregarious clutches with n − 1 females. However, sex ratios were male-biased in solitary clutches and female-biased in gregarious ones.

5. At the brood level (all wasps in a fig), a decrease in sex ratio with increasing brood size was only significant in one species, and sex ratio was unrelated to foundress number. In addition, figs with more foundresses contain more wasp offspring.

6. Finally, 10–22% of females developed in patches without males. As males are wingless, these females disperse unmated and are constrained to produce only sons from unfertilised eggs.

2. This study investigated how the koinobiont parasitoid wasps Asobara japonica and Leptopilina ryukyuensis regulate their larval growth when they parasitise host Drosophila larvae with varying larval periods.

3. In both parasitoid species, the preimaginal period was longer when they parasitised 1-day-old larvae of Drosophila rufa than when they parasitised older larvae of D. rufa or when they parasitised larvae of Drosophila simulans, a species with a shorter larval period than D. rufa. After host pupariation, A. japonica accelerated its growth, thereby showing a biphasic growth curve. On the other hand, L. ryukyuensis did not accelerate its growth after host pupariation.

4. Growth retardation of parasitoid larvae in 1-day-old D. rufa larvae would contribute to avoiding excess growth before host pupariation, because the excess growth of parasitoid larvae would have negative effects on host growth. The growth rate acceleration of A. japonica after host pupariation suggests that they enhance resource utilisation in a host that has reached maximum body mass. It remains uncertain as to why L. ryukuensis does not show clear accelerated growth after host pupariation. Nonetheless, these results suggest that parasitoid larvae have the ability to detect the developmental stage of hosts in a species-specific manner.

• Koinobiont parasitoids that allow hosts to develop continuously after parasitisation exhibit high flexibility in their development in order to consume host resources efficiently.
• The present study revealed that two koinobiont Drosophila parasitoids adjusted their larval growth rate in response to host conditions, i.e. they retarded their own development when they parasitised young or slowly developing host larvae.
• After host pupariation, one of these parasitoids accelerated development, whereas the other did not. This difference might reflect species-specific strategies of host resource use.

1. Bumblebee nests are difficult to find in sufficient numbers for well replicated studies. Counts of nest-searching queens in spring and early summer have been used as an indication of preferred nesting habitat, but this relationship has not yet been validated; high densities of nest-searching queens may indicate habitat with few nesting opportunities (meaning that queens have to spend longer looking for them).

2. From mid April 2010, queen bumblebees were counted along 20 transects in grassland and woodland habitats in central Scotland, U.K. The number of inflorescences of suitable forage plants were also estimated at each transect visit. The area surrounding each transect was searched for nests in the summer.

3. In total, 173 queen bumblebees were recorded on transects, and, of these, 149 were engaged in nest-searching. Searches subsequently revealed 33 bumblebee nests.

4. The number of nest-searching queens on transects was significantly, positively related to the number of nests subsequently found. Estimated floral abundance along the transect did not correlate with numbers of nest-searching queens or with the number of nests found, suggesting that queens do not target their searching to areas that are locally high in spring forage.

5. The data suggest that counts of nest-searching queens provide a useful positive indication of good nesting habitat, and hence where bumblebee nests are likely to be found later in the year.

• The number of nest-searching bumblebee queens in early spring was found to predict positively the number of nests subsequently found on transects through woodland and grassland.
• Estimated floral abundance along the transect did not correlate with numbers of nest-searching queens or with the number of nests found, suggesting that queens do not target their searching to areas that are locally high in spring forage.
• Using the distributions of nest-searching queens to target subsequent searches for nests may be a useful technique for increasing the success of researchers in locating bumblebee nests.

2. For aquatic insects that exploit detritus-based habitats, feeding conditions experienced during immature stages can influence fitness directly via effects on development and survivorship, but also indirectly by influencing adult traits such as fecundity and longevity.

3. Larval habitat age and prior resource exploitation were manipulated in a field experiment using the container mosquito Aedes triseriatus.

4. It was found that A. triseriatus from older habitats had greater larval survival, faster development and greater adult longevity. Exploitation of larval habitats by a prior cohort of larvae had a significant negative effect on subsequent cohorts of larvae by delaying development.

5. It is suggested that extended conditioning of detritus probably resulted in conversion of recalcitrant resources to more available forms which improved the quality of the habitat.

6. In a parallel study, evidence was found of carry-over effects of habitat age and prior exploitation on adult longevity for A. triseriatus and Aedes japonicus collected from unmanipulated aquatic habitats.

7. These results indicate the importance of detritus dynamics and the discontinuous nature of resource competition in these mosquito-dominated aquatic systems.

• Aquatic container habitats vary greatly in age and their history of use by prior non-overlapping cohorts of detritivorous mosquito larvae. In this study habitat age and prior use by larvae were manipulated.
• It was found that more larvae survived, they developed faster, and the resulting adults lived longer when reared in older habitats. It was also found that prior utilisation delayed development in the younger habitats.
• It is hypothesised that extended conditioning of leaf detritus increased the availability of recalcitrant nutrients, making older habitats of higher quality. Prior utilisation probably only has strong effects in poor-quality habitats.

2. Leaf harvesting followed a typical diel pattern of a 10–12 h foraging bout followed by a period of inactivity, while fruit harvesting occurred continuously, but with a regular pre-dawn dip in activity that marked a 24 h cycle.

3. Although the results of the present study are drawn from a single field colony, the difference found is consistent with a mechanism of negative feedback regulation acting in parallel on two resources that differ in their rates of distribution and processing, creating cycles of formation and depletion of material caches.

4. This hypothesis should provoke further interest from students of ant behaviour and some simple manipulative experiments that would begin to test it are outlined. Any role of resource caches in regulating foraging by Atta colonies may have similarities to the logistics of warehouse inventories in human economic activity.

• Distinct rhythmic cycles of harvesting two different resources, leaves and fruit, can be maintained by a single leaf-cutting ant colony.
• These rhythms may be controlled by backlogs of unprocessed leaf and fruit material that accumulate and diminish in the nest at different speeds.
• The role material caches play in the productive activity of leaf-cutting ant colonies may have parallels to the role of warehouses in supply chains in the human economy.

2. Less is known about how diversity impacts learning across the minutes and hours during which sensory environments of small foraging animals such as insects may vary dramatically.

3. This study shows that Drosophila melanogaster exposed to a diversity of odour–taste associations over a few minutes subsequently learn standard associative learning tasks poorly.

4. This effect is robust to variation in odours used in all parts of experiments.

5. Findings may have an impact on at least three major research areas in ecology: the relationship between biodiversity and ecosystem functioning; the evolution of floral constancy in pollinators; and the pest-protective effects of mixed species crops.

• A classic olfactory conditioning protocol for Drosophila is modified to examine the role of environmental diversity on learning in Drosophila melanogaster.
• Flies presented with a variety of odour–taste associations over a few minutes subsequently learn a standard olfactory–gustatory associative learning task poorly, relative to those exposed to a low diversity of associations.
• Such an effect could help to explain the relationship between biodiversity and ecosystem functioning, the evolution of floral constancy in pollinators, and the pest-protective effects of mixed species crops.

2. In this study, the role of Azteca alfari ants as biotic defence in individuals of Cecropia pachystachya was investigated experimentally with a simultaneous manipulation of both bottom-up (fertilisation) and top-down (ant exclusion) factors. Four treatments were used in a fully factorial design, with 15 replicates for each treatment: (i) control plants, without manipulation; (ii) fertilised plants, ants not manipulated; (iii) unfertilised plants and excluded ants and (iv) fertilised plants and ants excluded.

3. Fertilisation increased the availability of foliar nitrogen in C. pachystachya, and herbivory rates by chewing insects were significantly higher in fertilised plants with ants excluded.

4. Herbivory, however, was more influenced by bottom-up effects – such as the quality of the host plant – than by top-down effects caused by ants as biotic defences, reinforcing the crucial role of leaf nutritional quality for herbivory levels experienced by plants. Conditionality in ant defence under increased nutritional quality of leaves through fertilisation might explain increased levels of herbivory in plants with higher leaf nitrogen.

• In this study, the role of ants as biotic defence in individuals of a tropical ant-plant was investigated experimentally with a simultaneous manipulation of plant quality and ant defence.
• Fertilisation increased the availability of foliar nitrogen, and herbivory rates were significantly higher in fertilised plants (F) with ants excluded (AE).
• Although top-down factors were important in determining herbivory, the study reinforced the crucial role of leaf nutritional quality for herbivory levels experienced by plants and the conditionality of ant defence.

2. Wind-pollinated plants, in particular, which are almost never studied in plant–pollinator networks, can alter insect-pollinated plants' attractiveness through competition for nutrients. The response of pollinators to such changes has never been investigated.

3. A pot experiment was carried out in which an insect-pollinated species, Echium plantagineum, was grown in binary mixture with three wind-pollinated species selected to exert a panel of competitive interactions. Below-ground competition was controlled using dividers limiting interspecific root competition. Floral traits of E. plantagineum (i.e. flower production, floral display size, flower size and nectar production) were measured. For each species mixture, the visits (i.e. first visit, number of visits, 10-min sequences) of Bombus terrestris individuals released in a flight cage containing two pots were followed, one with and one without below-ground competition.

4. Below-ground competition significantly affected nectar's sucrose concentration but did not influence flower and nectar production. Likewise, pollinator visits were not influenced by below-ground competition. Competitor identity significantly influenced flower and reward production of E. plantagineum, with a decrease in the presence of the most competitive wind-pollinated species. A tendency for faster flower visitation events was also detected in the presence of the least competitive competitor. This study raises new questions regarding the influence of wind-pollinated plants on plant–pollinator interactions.

2. The objective of the present study was to determine how the feeding of larvae on each of the two host plants impacts oviposition, offspring survival and fecundity in Y. evonymellus. Our hypothesis was that, under controlled conditions, females will lay eggs on the host on which they fed as larvae. We also hypothesised that the lower survival of young larvae feeding on P. serotina was due to the smaller buds and leaves present in this species, relative to those of P. padus.

3. A dual-choice experiment conducted under laboratory conditions demonstrated that females preferentially chose to oviposit on the plant species on which they fed as larvae. In the experiment, potential fecundity and offspring survival were significantly higher on P. padus than on P. serotina. The reduced performance of Y. evonymellus on P. serotina was correlated with a smaller bud mass and volume, lower leaf mass and surface area, and difficulty in constructing a protective tent against unfavourable weather conditions.

4. In summary, the identity of the host plant species during larval feeding determines adult oviposition preference for that host species. The survival of larvae on P. serotina growing in the nature is low, but for phenology-related reasons.

• Yponomeuta evonymellus females preferentially chose to oviposit on the host plant species on which they had fed as larvae.
• Potential fecundity of females and the survival of their offspring were significantly higher on native to Europe Prunus padus than on non-native P. serotina.
• The reduced survival of Y. evonymellus offspring on P. serotina was correlated with a smaller bud mass and volume, lower leaf mass and surface area, and difficulty in constructing a protective tent against unfavourable weather conditions.

2. To test this hypothesis, the ecological stoichiometry and the interaction network frameworks were combined. The food preferences of 24 plant species by 23 grasshopper species were determined, and the N and P contents of both trophic levels were measured. The weighted mean P and N contents of the consumed plants, which represent the grasshoppers' feeding niche, were highly correlated, indicating that the grasshoppers' diets are spread along a single functional niche axis. The links between the stoichiometry of the plants and their consumers were then tested with the fourth corner analysis, a multivariate technique combining the plant traits, the insect traits and the interaction network.

3. In line with the earlier hypothesis, P-rich grasshoppers consumed plants high in N and P, probably because their growth rate is higher. These findings therefore introduce a mechanism that accounts for interspecific differences in diet preference. They also contribute to an understanding of how herbivore communities might respond to P and N limitation in ecosystems, and how complex interaction networks can influence biogeochemical cycles of N and P.

Mean leaf N and P contents consumed by 23 grasshopper species choosing among 24 plant species are highly correlated, defining a unique nutritional axis.

The grasshopper body P content (but not body N content) is correlated with the mean N and P content of the consumed leaves.

If differences in body P content across grasshopper species reflect different growth rates, contrasting plant preferences for P and N may fulfil their nutritional requirements.

2. One such species, Micrurapteryx salicifoliella, must initially enter leaf cells directly from an egg adhered to the cuticle, but later instars can move between leaves and initiate new mines from the leaf exterior.

3. Natural patterns of occurrence by M. salicifoliella were quantified on 10 sympatric Salix species varying in trichome expression to test whether trichomes were associated with reduced oviposition, larval survival and leaf damage.

4. Mean egg density and leaf mining damage were negatively related to mean trichome density across Salix species. Survival of M. salicifoliella from egg to pupa was positively related to trichome density, suggesting that initiation of new mines by late-instar larvae was not adversely affected by trichomes. There was no evidence that trichomes benefited leaf miner larvae indirectly by decreasing density-dependent mortality; rather, the positive relationship between trichome density and larval survival may reflect less effective chemical defence by Salix species expressing high trichome density.

5. The results suggest that foliar trichomes serve as an effective defence against M. salicifoliella by deterring oviposition, but do not reduce the survivorship of those individuals that successfully transition from egg to larva.

The leaf miner Micrurapteryx salicifoliella has specialised morphology requiring direct egg–leaf contact for successful hatching. Trichome density across 10 Salix species was negatively associated with oviposition by this lepidopteran species.

However, trichomes were positively associated with larval survival, possibly due to trade-offs between physical and chemical defence.

Overall, trichome density was negatively related to leaf-mining damage among Salix species, suggesting that foliar trichomes can function as an effective defence by deterring herbivore oviposition.

2. To test this hypothesis, a field cage experiment was conducted in which Aphis glycines populations initiated with controlled proportions of apterous and alate individuals were exposed to predation, while predator-free space was accessible only through flight. It was predicted that an investment in alate individuals would benefit a population under predation, regardless of associated costs to fecundity.

3. As expected, a strong trade-off was observed between fecundity and wing development. However, populations initiated with a fixed proportion of alate and apterous individuals showed no reductions in final population size compared with populations initiated with apterous individuals exclusively. Moreover, the initial presence of alate individuals in the populations increased aphid prevalence (i.e. proportion of plants colonised). Similarly, both increased population size and prevalence were observed when predator-free space was accessible through flight, as opposed to when it was inaccessible.

4. These results show that despite high costs to fecundity, an investment in alate individuals is neither beneficial nor detrimental to population size when predator-free space is accessible, but increases aphid prevalence. It is concluded that prevalence might provide an ecological advantage important enough to warrant the production of alate morphs under intense predation.

In a soybean aphid (Aphis glycines Matsumura) population under predation, predator-free space colonisation by alate individuals increased population size and aphid prevalence (i.e. proportion of plants colonised).

Despite lower fecundity by alate individuals, the initial presence of this morph in an A. glycines population under predation increased aphid prevalence, with only a temporary decrease in population size.

We conclude that increased prevalence might provide an ecological advantage important enough to warrant the production of alate morphs by an aphid population under predation.

2. This study investigated the effects of a protective symbiont (Hamiltonella defensa) in pea aphids (Acyrthosiphon pisum) on hyperparasitoids, which are a trophic level above the natural enemy target of the symbiont (primary parasitoids).

3. Pea aphids, with and without their natural infections of H. defensa, were exposed first to a primary parasitoid against which the symbiont provides partial protection (either Aphidius ervi or Aphelinus abdominalis), and second to a hyperparasitoid known to attack the primary parasitoid species.

4. It was found that hyperparasitoid hatch rate was substantially affected by the presence of the symbiont. This effect appears to be entirely due to the removal of potential hosts by the action of the symbiont: there was no additional benefit or cost experienced by the hyperparasitoids in response to symbiont presence. The results were similar across the two different aphid–parasitoid–hyperparasitoid interactions we studied.

5. It is concluded that protective symbionts can have an important cascading effect on multiple trophic levels by altering the success of natural enemies, but that there is no evidence for more complex interactions. These findings demonstrate that the potential influence of protective symbionts on the wider community should be considered in future food web studies.

Bacterial symbionts can protect their aphid hosts against parasitoids.

We investigated whether protective symbionts affect hyperparasitoids at the trophic level above aphid parasitoids.

We found that protective symbionts significantly reduce numbers of hatching hyperparasitoids by reducing the number of available parasitoid hosts, but there is no evidence of more complex interactions between symbionts and hyperparasitoids.

2. Larvae were reared under a factorial array of two photoperiods (LD 10:14 h and LD 14:10 h) and two food availability regimes (leaves ad libitum and available every other day) to assess the frequency of green and brown pupae. Field survival of green and brown pupae was quantified in three commonly used habitats that differ in background coloration (cacti, rocks and shrubs).

3. Food availability determined pupal colour. Larvae in the ad libitum regime resulted mostly in green pupae, while those with restricted food were mostly brown. In contrast, photoperiod did not influence pupal colour. Survival probability of pupae placed on cacti was higher than those placed on rocks and shrubs, and the lowest predation risk across habitats was for green pupae on cacti.

4. Food availability plays a major role in the seasonal polyphenism for pupal colour of specialist butterflies inhabiting arid environments with winter rains.

Food availability plays a major role in the seasonal polyphenism for pupal colour of specialist butterflies inhabiting arid environments with winter rains where day length does not positively covary with host productivity.

Food availability determines pupal coloration. An ad libitum food regime results in green pupae, while restrictions in food regimen yield brown pupae. By contrast, photoperiod does not influence pupal colour.

Survival probability of pupae placed on cacti is higher than those placed on rocks and shrubs, with green pupae on cacti exhibiting the lowest predation risk across habitats.

2. Egg maturation patterns and related life-history traits were studied in the polyembryonic parasitoid wasp, Copidosoma koehleri (Hymenoptera: Encyrtidae). Although the genus Copidosoma was previously reported to be fully pro-ovigenic, mean egg loads of host-deprived females almost doubled within their first 6 days of adulthood.

3. The initial egg-loads of newly emerged females were determined and age-specific realised fecundity curves were constructed for their clone-mate twins. The females' initial egg loads increased with body size, but neither body size nor initial egg load was correlated with longevity and fecundity.

4. The variation in initial egg loads was lowest among clone-mates, intermediate among non-clone sisters and highest among non-sister females. The within-clone variability indicates environmental influences on egg maturation, while the between-clone variation may be genetically based.

5. Ovaries of host-deprived females contained fewer eggs at death (at ∼29 days) than on day 6. Their egg loads at death were negatively correlated with life span, consistent with reduced egg production and/or egg resorption. Host deprivation prolonged the wasps' life span, suggesting a survival cost to egg maturation and oviposition.

6. It is concluded that adult fecundity and longevity were not traded off with pre-adult egg maturation.

Initial egg loads in the polyembryonic parasitoid, Copidosoma koehleri (Hymenoptera: Encyrtidae), vary among females. The variation is lowest among clone-mates, intermediate among non-clone sisters and highest among non-sister females.

The females' initial egg loads increased with body size. Body size and initial egg loads did not correlate with longevity and fecundity. Host deprivation prolonged the wasps' life span.

These results suggest that pre-adult egg production is not traded off with longevity, but that egg maturation and oviposition at the adult stage carry a survival cost.

2. The generality of ovipositing Culex to the presence of three, widespread larvivorous fish species was tested in a set of field experiments with artificial oviposition pools using caged fish.

3. Larval performance was further examined under actual predation by these three fish species.

4. Results show that ovipositing females responded strongly to the presence of caged mosquitofish, Gambusia affinis, while showing no significant response to the presence of caged green sunfish, Lepomis cyanellus, or the pirate perch, Aphredoderus sayanus. All three fish species consumed similar amounts of larvae.

5. This is the first example of species-specific response differences to predators during mosquito oviposition habitat selection. These results point to the existence of predator-released kairomones affecting mosquito behaviour. These kairomones may either be species-specific or vary in concentration among fish, and probably have an important role in the understanding of mosquito spatial distribution.

Several mosquito species avoid ovipositing in pools containing fish.

We show that ovipositing Culex distinguish among fish species.

This response cannot be explained by predator efficiency differences.

2. The influences of aphid clonal identity and host plant (Vicia faba) intraspecific genetic variation on the performance of five genotypes of pea aphid (Acyrthosiphon pisum) were investigated – with and without interaction with a competing heterospecific clone of vetch aphid (Megoura viciae) – across three cultivars of V. faba.

3. Pea aphid performance in the presence of a competing vetch aphid clone (G × G × E) compared with the absence of competition (G × E) revealed strong context-dependent, genotype-specific shifts in performance, influenced by plant cultivar, competitor presence and their interaction.

4. The performance of vetch aphid in competition with each pea aphid clone was also compared. Here, competitor's genotype and abundance underlay a remarkably varied response by vetch aphid across interactions.

5. The study shows that aphid genotypes exhibit a varying degree of risk spreading, contingent on competitor identity and the patterns of aggregation across three plant cultivars. Owing to feedback loops between species activities and selective forces acting on them, our findings suggest that there are context-dependent responses by competitors that are shaped via the interplay of the co-occurring species and their biotic environment.

6. This work highlights the complexity of species interactions and the importance of investigating reciprocity between competition and intraspecific genetic variation. A better understanding of the eco-evolutionary interactions between phloem-feeding insects and their host plants can potentially be used to enhance crop protection and pest control.

We found that the growth rate of five pea aphid genotypes changed when competing with a vetch aphid clone across three faba bean cultivars, where the different genotypes responded differently.

We also found that the aggregation of the pea aphid genotypes on the plant varied as a function of competition and the plant cultivar on which the interaction took place.

The vetch aphid also adapted its strategy (performance and aggregation) with regard to competing pea aphids. The context and identity G × E versus G × G × E matter in aphid competition.

2. Manipulative experiments were used to test whether higher levels of dung beetle species richness enhanced individual functions and multifunctionality, and whether these relationships were influenced by perturbation (in this case, non-target exposure to the veterinary anthelmintic ivermectin). The four ecosystem functions tested were dung removal, primary productivity, soil faunal feeding activity and reduction in soil bulk density.

3. For individual functions, perturbation had limited effects on functioning, with only dung removal significantly (negatively) affected. Species richness did not, on its own, explain significant variation in the delivery of individual functions. In the case of primary productivity, an interaction between richness and perturbation was found: species-rich dung beetle assemblages enhanced forage growth in the unperturbed treatment, relative to the perturbed treatment.

4. Using a composite ‘multifunctionality index’ it was found that species-rich dung beetle assemblages delivered marginally higher levels of multifunctionality in unperturbed conditions; however, this benefit was lost under perturbation. Using a relatively new and robust method of assessing diversity–multifunctionality relationships across a range of thresholds, no significant effect of species richness on multifunctionality was found.

Dung beetles are a species-rich insect group that support pasture production by feeding on and burying the dung of livestock.

We tested whether dung beetle species richness influenced four ecosystem functions, individually and in combination, and whether this relationship was affected by exposure to residues of ivermectin, a veterinary anthelmintic.

Effects of experimental manipulations were weak, but there was evidence that species-rich dung beetle assemblages increase functioning when multiple ecosystem functions were considered simultaneously and in the absence of ivermectin.

2. This demonstrated specificity and a dearth of studies on Hamiltonella in the field prompted the authors to quantify parasitism rates of Hamiltonella-infected and -uninfected Aphis craccivora Koch aphid colonies in a manipulative field study.

3. It was found that A. craccivora in central Kentucky alfalfa were parasitised by Lysiphlebus testaceipes (Cresson) and Aphelinus sp. Surprisingly, Hamiltonella infection did not lower successful parasitism by the naturally occurring parasitoid wasps. Whether Hamiltonella was effective against L. testaceipes was subsequently tested in a controlled laboratory assay, and no effect on parasitism rate was found.

4. This study emphasises the fact that defensive symbionts sometimes provide no tangible defensive benefits under field conditions, depending on parasitoid community composition. It is hypothesised that the protective mutualism may be beneficial in geographically localised areas. When the symbiosis is effective against a local parasitoid community, aphid clones may experience eruptive population growth and rapidly disperse across a large area, allowing spread to habitats with different parasitoid communities where the mutualism is an ineffective defence.

Among Aphis craccivora in a central Kentucky alfalfa field, we demonstrate experimentally that Hamiltonella infection did not lower successful parasitism by naturally occurring parasitoid wasps.

Hamiltonella was also ineffective against the most common parasitoid wasp species in a controlled laboratory assay.

Our work emphasises the fact that defensive symbionts sometimes provide no tangible defensive benefits under field conditions, depending on parasitoid community composition.

2. The present study evaluated the effects of host plant secondary metabolites (salicylates, flavonoids, condensed tannins), physical traits (trichome density), nutrient content (N:C) and phylogeny on the abundance and richness of gall-forming arthropods associated with eight willow species and Populus tremula.

3. Galler abundance was affected by N:C rather than by willow defensive traits or phylogeny, suggesting that gallers respond differently to host plant traits than to less specialised guilds, such as leaf-chewing insects. None of the studied defensive traits had a significant effect on gall abundance. Gall morphospecies richness was correlated with the host phylogeny, mainly with the nodes representing the inner division of the willow subgenus Vetrix. This suggests that the radiation of some willow taxa could have been important for the speciation of gallers associated with willows.

4. In conclusion, it is shown that whereas willow traits, such as nutrient content, appeared to affect abundances of gallers, it is probably willow radiation that drives galler speciation.

We studied gall abundance and richness on willows to illustrate the processes maintaining one of the richest assemblages of gall formers associated with a single genus of host plants.

Integrated information on willow defences, nutrient content and phylogeny shows that the abundance of gallers on willows is affected mainly by leaf nutrient content.

On the other hand, the richness of gallers was affected mainly by willow phylogeny, suggesting that it is probably willow radiation driving galler speciation.

2. Here the rate of senescence in 22 species of Lepidoptera was quantified by fitting demographic models to adult survivorship data drawn from a range of field and laboratory studies.

3. Senescence was evident in all 22 species investigated, with a model of age-related mortality consistently fitting the survivorship curves significantly better than an alternative model which assumes constant mortality.

4. The rates of senescence varied significantly among species. The rates of senescence also differed significantly between sexes for all species tested, but not in a consistent way.

Recent observations of actuarial senescence – an increase in mortality rate with age – have challenged the assertion that the brevity of adult insect life spans precludes ageing.

Here we quantified the rate of senescence in 22 species of Lepidoptera by fitting demographic models to adult survivorship data drawn from a range of field and laboratory studies.

Senescence was evident in all 22 species investigated, with a model of age-related mortality consistently fitting the survivorship curves significantly better than an alternative model that assumes constant mortality.

2. Plants of the selenium accumulator, Raphanus sativus (wild radish), were watered with three different selenium treatments (0, 0.25 or 0.5 µg Se ml⁻¹). Aphids, Myzus persicae, and Argentine ant colonies, Linepithema humile, were added to each caged plant and allowed to interact freely. Ant colonies were supplemented with one of three different food options to encourage the consumption of aphids, aphid honeydew, or aphids and honeydew.

3. The accumulation of selenium by each trophic group and a trophic transfer factor (TTF) was calculated. The TTF for plants to aphids was > 1, indicating biomagnification, whereas the TTF for aphids to worker ants was < 1, indicating only biotransfer. Accumulated levels by worker ants did not statistically differ as a result of diet.

4. The amounts of selenium acquired by ants as a factor of diet and caste were compared. Plants, aphids and worker ants accumulated selenium in a dose-dependent manner. Ant queens did not contain detectable amounts of selenium. Honeydew contained comparable amounts of selenium to plant selenium levels.

5. Access to toxic compounds via honeydew and insect protein may have negative effects on the range expansion of invasive species, such as the Argentine ant.

2. Caterpillars were surveyed in four cerrado localities in southeast Brazil (70–460 km apart). The efficacy of caterpillar defensive traits against predation by two common ant species (Camponotus crassus, C. renggeri) was assessed through experimental trials using caterpillars of different species and captive ant colonies.

3. Although ant presence can reduce caterpillar infestation, the ants' predatory effects depend on caterpillar defence traits. Shelter construction and morphological defences can prevent ant attacks (primary defence), but once exposed or discovered by ants, caterpillars rely on their size and/or behaviour to survive (secondary defence).

4. Defence efficiency depends on ant identity: C. renggeri was more aggressive and lethal to caterpillars than C. crassus. Caterpillars without morphological defences or inside open shelters were found on plants with decreased ant numbers. No unsheltered caterpillar was found on plants with extrafloral nectaries (EFNs). Caterpillars using EFN-bearing plants lived in closed shelters or presented morphological defences (hairs, spines), and were less frequently attacked by ants during trials.

5. The efficiency of defences against ants is thus crucial for caterpillar survival and determines host plant use by lepidopterans in cerrado. Our study highlights the effect of EFN-mediated ant-plant interactions on host plant use by insect herbivores, emphasizing the importance of a tritrophic viewpoint in risky environments.

We investigate whether caterpillars with morphological or behavioural defences have decreased risk of falling prey to ants, and if defence traits mediate host plant use in ant-rich cerrado savanna.

Caterpillars without morphological defences or inside open shelters were found on plants with fewer ants. Caterpillars using ant-visited plants (with extrafloral nectaries) lived in closed shelters or presented morphological defences.

Efficient defence against ants is crucial for caterpillar survival and mediates host plant use by lepidopterans in cerrado. Our study highlights the importance of a tritrophic viewpoint in risky environments.

2. The applicability of this hypothesis in florivory, however, generally lacks a mechanistic understanding of the effect of resource density on neural constraint, so using caged experiments, the (i) ability of a generalist, floriphilic katydid [(Phaneroptera brevis (Serville)] to find a floral resource (inflorescences of Bidens pilosa L.), (ii) attentiveness of the katydid on this resource after successfully detecting the floral resource, and (iii) efficiency of resource use under varying densities of the floral resource were studied.

3. The present results indicated no evidence of an obvious effect of floral resource density on the detection of resources by the florivore but an increase in floral-resource density generally led to lower efficiency and attentiveness in the foraging katydids.

4. These findings provide the first evidence of the neural constraint hypothesis in the context of resource density and corroborate the applicability of the neural constraint hypothesis in florivory.

The present results indicated that increase in floral-resource density generally led to lower efficiency and attentiveness in the foraging floriphilic katydids.

The first evidence of the neural constraint hypothesis in the context of resource density is provided.

The applicability of the neural constraint hypothesis in florivory is also corroborated.

2. A subset of the 17 years of grasshopper density data from the Wyoming Grasshopper Survey Dataset was used to explore associations among grasshopper species.

3. Associations of certain species were found with over 80% confidence. Life-history traits of those species commonly found together were examined and compared (a posteriori), creating opportunities to hypothesise certain ecological relationships (e.g. interspecific competition, indirect mutualism) for future studies.

4. This case study shows that further MBA analysis of grasshopper assemblages should prove useful in discovering ecological relationships of grasshopper species during outbreaks. Preliminary examples are demonstrated.

2. Two plant taxa, Lavandula angustifolia and Canna ‘sp.’, with differing floral morphology, were used to compare the value of DVR and direct observations in estimating honeybee (Apis mellifera) visitation, flower density and number of flowers visited per foraging bout.

3. The two methods yielded identical results when observing the structurally simple L. angustifolia at both high (10.54 ± 0.52 per plant) and low honeybee density (2.24 ± 0.20 per plant). However, DVR underestimated the number of flowers scored in the field of view (28.7 ± 1.8 direct vs. 22.7 ± 0.9 DVR), the number of honeybees observed (5.3 ± 0.8 direct vs. 3.7 ± 0.7 DVR) and the number of flowers visited during foraging bouts (8.3 ± 1.2 direct vs. 5.5 ± 1.0 DVR) on the more complex Canna ‘sp.’

4. It is concluded that portable weatherproof DVR devices such as the GoPro Hero are valuable tools for pollination biologists, allowing a single researcher to make simultaneous observations of multiple plants in one or more sites, whilst also allowing the footage to be reviewed. However, DVR devices are limited by their depth and field of view when target plants are large or structurally complex.

2. The present study investigated the population dynamics of a specialised aphid (Metopeurum fuscoviride) on its patchily distributed host plant (Tanacetum vulgare) and associated community of mutualistic ants and predators in a small-scale field site. Furthermore, aphid habitat differences (plant size, C/N ratio, location and surrounding vegetation) were quantified, and seasonal timing and precipitation were considered.

3. Seasonal timing and precipitation both had effects on aphid colonisation, extinction events and aphid colony persistence. Towards the end of the season, and after higher precipitation, aphid colonisation events decreased and extinction events increased. Plant size and location as well as aphid within-field dispersal determined the spatio-temporal distribution of aphid colonies.

4. Mutualistic ants (Lasius niger and Myrmica rubra) increased the chance of establishment of aphid colonies. However, when M. rubra was tending, aphid colony persistence was reduced. Aphid persistence and extinction were dependent on aphid abundance, as a higher colony size reduced the probability of extinction by predation.

5. The results emphasise the importance of dispersal limitation, population growth and the presence of mutualists when studying the spatio-temporal dynamics of tansy aphids, particularly in a small-scale field site.

• Tansy aphid metapopulations are not only structured by dispersal limitations and population growth but also by the biotic community in which they live.
• Mutualistic ants shape the metapopulation structure of tansy aphids by increasing the colonisation success of empty plant patches.
• Top-down predation effects do not exclusively drive aphid metapopulation structuring in this system, it is rather a combination of many factors acting at the same time.

2. Laboratory experiments were conducted to evaluate the effects of paternal care by K. deyrolli against the ant Tetramorium tsushimae by means of four treatments: attending male with ant approach (WM-WA); no attending male with ant approach (NoM-WA); attending male without ant approach (WM-NoA); and no attending male without ant approach (NoM-NoA).

3. The rate of offspring survival was lower in the NoM-WA group (45.3%) than in any other group, which showed similar offspring survival (WM-WA = 80.4%, WM-NoA = 75.1%, NoM-NoA = 80.3%). Moreover, there were a total of 44 interactions between the attending male and ants in WM-WA, and of these, a chemical compound was released by the attending male four times; this probably deterred ants from attacking because the ants went back to their colony.

4. In conclusion, the attending male can protect its eggs from ant predators and its care has an important role. To the best of the authors' knowledge, this is the first report of Lethocerinae males protecting their egg masses from ants by means of physical and chemical defence.

2. Foliage quantity and quality of red alder, Alnus rubra, were manipulated together with the presence of non-entomopathogenic phylloplane bacteria to investigate their impacts, singly and in combination, on survival, pupal mass, growth rate, fecundity and egg quality of a cyclic forest insect, the western tent caterpillar, Malacosoma californicum pluviale.

3. Food limitation (half food) had strong negative impacts on all life-history traits. When the larvae were fed continuously, however, neither ingesting phylloplane bacteria nor eating leaves from damaged branches (induced foliage) affected survival. In the half-food treatment, ingesting bacteria further increased mortality, while feeding on induced foliage improved survival.

4. Growth rate and pupal mass of both sexes were reduced for larvae with food limitation compared with continuously fed insects and this was exacerbated when the larvae also ate bacteria-treated leaves. A combination of bacteria and induced foliage also reduced larval growth rate by 5% in the full-food treatment.

5. Fecundity (eggs per egg mass) was 2.7 times greater in full-food than in food-limited treatments but neither phylloplane bacteria nor plant induction had an effect. Insects fed induced foliage produced smaller eggs. Overall, there was no evidence of a three-way interaction between the three stressors, although there were negative synergistic effects, primarily between food limitation and the ingestion of phylloplane bacteria.

• Organisms are subjected to multiple stressors in natural situations; however, the impacts of combined stressors on fitness are rarely assessed.
• Here we show that the combination of food limitation and phylloplane bacteria had negative synergistic effects on survival, growth rate and pupal mass, but feeding on induced foliage had mixed effects.
• Fecundity was only reduced by food limitation but insects fed damaged leaves produced smaller eggs.

2. First, the efficiency of the S. nanjingensis (prey) counterattacking T. bambusae (predator) was observed. The prey females frequently locked the immature predators out of their nests using silk web, and the predators subsequently died of starvation. Furthermore, the prey males often killed immature T. bambusae mites after they invaded the nests.

3. This reversal of roles in the predator–prey system was then re-reversed (returned to a normal state) by the behaviour of T. bambusae females. Immature predators could maintain their predacious natures due to the presence of attending adult females, which are able to cope with the prey counterattack behaviours.

2. The predation pressure on geometrid larvae and pupae over an elevational gradient was tested. The effects of background larval density and bird occupancy of monitoring nest boxes on predation rates were also tested. Predation on larvae was tested through exclusion treatments at 20 replicate stations over four elevations at one site, while pupae were set out to measure predation at two elevations at three sites.

3. Larval densities were reduced by bird predation at three lower elevations, but not at the highest elevation, and predation rates were 1.9 times higher at the lowest elevation than at the highest elevation. The rate of predation on larvae was not related to background larval density or nest box occupancy, although there were more eggs and chicks at the lowest elevation. There were no consistent differences in predation on pupae by elevation.

4. These results suggest that elevational variation in avian predation pressure on larvae may help to drive elevational differences in outbreak tendency, and that birds may play a more important role in geometrid population dynamics than the focus on invertebrate and soil predators of previous work would suggest.

2. In a field experiment, habitat size and hydroperiod were manipulated independently in water-filled containers, to test these hypotheses about processes structuring aquatic communities. Human-made containers were used that are dominated by mosquitoes that vary in desiccation resistance, competitive ability, and predation resistance.

3. Habitat size and drying had significant effects on abundances of larvae of the common species in these communities. There was sorting of species by habitat size and by drying, with species that are better competitors relatively more abundant in smaller, more ephemeral habitats, and predator-resistant, slower-developing species relatively more abundant in larger or permanently flooded habitats. There were no detectable effects of habitat size or drying on the dominant predator.

4. Habitat size and its interaction with drying affected inputs of eggs to containers. Habitat size also affected relative abundances of the two dominant species in the egg population.

5. Although habitat size and hydroperiod significantly affected composition of these communities, these impacts did not appear to be mediated through effects on predator abundance. Species-specific differences in habitat size and drying regime preferences, and habitat-dependent larval performance appear to be the main forces shaping these communities.

2. Using an integrative approach that links ecological processes (behavioural choices of insects) with physiological plant mechanisms (nutrient and phytohormone levels) for the wild crucifer Brassica nigra (L.) Koch., this study evaluates preferences of leaf chewers for plants previously infested with several densities of the specialist aphid Brevicoryne brassicae L. (Hemiptera, Aphididae). As leaf chewers, four species of caterpillars (Lepidoptera) were selected that differ in their degree of specialisation in crucifers.

3. These results show that, whereas at low and medium aphid densities caterpillars displayed a preference for aphid-infested plants or no preference, at high aphid infestation density, all four species of caterpillar preferred uninfested plants, with a significant difference for Pieris rapae and Mamestra brassicae.

4. In contrast to our expectation, the consistent preference for uninfested plants at a high aphid density could not be associated with a decrease in plant nutrition. However, while jasmonate concentrations [i.e. 12-oxo-phytodienoic acid and jasmonic acid (JA)] at medium aphid-density infestation decreased compared with low levels of infestation, at high infestation level, the jasmonates JA as well as JA conjugated with the amino acid isoleucine were present at higher levels compared with low-infestation treatments.

5. This work provides evidence that positive interactions observed in herbivore communities can be transient, leading to negative interactions mediated by changes in plant defences rather than in plant nutrition.

2. In this study, grazing intensities (ungrazed, moderate, and heavy) were manipulated and precipitation (ambient and increased amount of rainfall) altered in a field experiment to test the effects of grazing and altered precipitation on a grasshopper community in a meadow steppe in northeastern China.

3. It was found that grasshopper species richness did not change according to different grazing intensities under ambient precipitation, but was significantly higher (by 38.1%) in moderate grazing intensities under increased precipitation. Grasshopper abundance increased considerably with increasing grazing intensities in ambient precipitation treatments; however, grasshopper abundance in heavy grazing intensities was significantly lower (by 32.9%) than in the other two grazing intensities under increased precipitation. Moreover, the responses of grasshopper abundance to grazing under altered precipitation were species-specific.

4. Grazing effects on grasshopper species diversity were mediated through the species richness and biomass of grasses (food resources), but the effects on grasshopper abundance were mediated through plant height (vegetation structure) under altered precipitation.

5. These results suggest that appropriate grazing by large herbivores would be considered as beneficial management practices for maintaining grasshopper diversity and abundance under conditions of increased precipitation in grassland ecosystems. Additionally, greater attention should be paid to the population dynamics of different grasshopper species to better understand the responses of grasslands to grazing and altered precipitation.

2. A native crab spider, Xysticus elegans, was placed on one cluster in a small array of Baccharis pilularis inflorescence clusters, and the preferred short-range foraging distances of naturally visiting pollinators was determined.

3. Nearly all pollinator taxa (honey bees, wasps, other Hymenoptera, and non-bombyliid flies) spent less time foraging on the predator cluster.

4. The key result of this study is that inflorescences within 90 mm of the crab spider were avoided by visiting honey bees and wasps, which spent three- and 18-fold more time, respectively, foraging on more distant flower clusters.

5. Whether honey bees can use olfaction to detect spiders was then tested, and this study provides the first demonstration that honey bees will avoid crab spider odour alone at a food source.

• Nearly all pollinator taxa (honey bees, wasps, other Hymenoptera and non-bombyliid flies) spent less time foraging on the predator cluster.
• Visiting honey bees and wasps avoided inflorescences within 90 mm of the crab spider: they spent three- and 18-fold more time, respectively, foraging on more distant flower clusters.
• Whether honey bees can smell spiders was then tested, and this study provides the first demonstration that honey bees will avoid crab spider odour alone at a food source.

2. Preliminary observations on Ennya maculicornis (Membracidae: Similinae: Polyglyptini) show that females generally lay a single egg mass, and occasionally two or three egg masses, and that maternal care is a plastic trait because some females abandoned their egg mass before it hatched while other females remained with their offspring after egg hatching. These features make this species an interesting model to study the relationship between female fitness, maternal care and ecological factors such as oviposition site.

3. The biology and natural history of E. maculicornis are described and the relationships in question analysed using demographic parameters estimated by matrix models. Ennya maculicornis showed sexual dimorphism and a longer developmental period than other species of the same tribe. Females exhibited maternal care that increased offspring survival, and preferred mature over young host leaves for oviposition. Finite rate of increase (λ) values were lower than 1, suggesting a tendency towards population decrease.

4. The results represent the first detailed description of the life history and ecology for a species of this genus. Additionally, new hypotheses for treehopper sexual dimorphism, oviposition site choice and the ecological effects on population dynamics are proposed.

2. This study investigated whether conspecifics during larval growth can influence and modify the decision to orient to different quality hosts in a parasitoid with an active host-seeking larva. How the density of conspecifics during growth modifies these decisions was also studied.

3. When larvae were submitted to increases in the intensity of pre-parasitism competition and then offered different host odours, they increased the orientation to poor-quality hosts likewise. It was also found that this behaviour is general to orientation to hosts in different physiological states.

4. These results show that pre-parasitism competition can influence and modulate orientation to poor-quality hosts when high-quality hosts are not available.

• Increasing the intensity of intraspecific competition lowers the host selectivity threshold in a density-dependent way.
• Increasing the density of conspecifics increases the orientation to sub-optimal hosts' odours in a linear fashion.
• Modulation of the orientation to sub-optimal host odours is a general response to every sub-optimal host.

2. Feather mites are permanent ectosymbionts of birds assumed to be transmitted mainly vertically from parents to offspring. The transmission of Proctophyllodes doleophyes Gaud (Astigmata, Proctophyllodidae) was studied in two European populations of pied flycatchers, Ficedula hypoleuca Pallas (Passeriformes, Muscicapidae).

3. The vertical transmission of this mite species is demonstrated here with an acaricide experiment. This study also compared (for two distant populations during 4 years) patterns in reductions in mite intensity in adult birds, from egg incubation to chick-rearing periods, with the predictions of three hypotheses on how host survival prospects and mite intraspecific competition might drive feather mites' transmission strategy.

4. The results are in agreement with previous studies and show that feather mites transmit massively from parents to chicks.

5. The magnitude of the transmission was closer to that predicted by the hypothesis based on intraspecific competition, while a bet-hedging strategy is also partially supported.

• The adaptive causes of symbiont transmission strategies are little understood. Here we studied the vertical transmission of ectosymbiotic mites living on bird feathers.
• We found that feather mites transmit massively from parents to chicks even though adult birds are considered to be safer hosts.
• We compared the observed transmission patterns with hypothetical predictions and concluded that massive transmission could be interpreted as a way to reduce intraspecific competition or to spread the risk of host mortality.

2. In the present study, it was found that nymphs of the cricket Velarifictorus aspersus ate unfertilised eggs regardless of whether there was other food available. This provision enabled nymphs to develop successfully when no other food was provided, and to gain additional body mass when other food was available under crowded conditions. These results suggest that unfertilised eggs have an important role in the survival and development of nymphs.

3. Nymphs preferred to eat unfertilised rather than fertilised eggs, suggesting that they may have the ability to distinguish between these two types of eggs.

4. Crowding promoted feeding on unfertilised eggs and accelerate nymphal development, suggesting that greater food consumption accounts for faster growth under grouped conditions.

2. Oviposition bioassays were conducted by releasing gravid mosquitoes into field enclosures with automobile tires containing low and high concentrations of the chemical blend, and water controls. The offspring were then reared in water collected from the tires in which they were deposited.

3. Aedes albopictus and wild Cx. quinquefasciatus laid more eggs in the chemical blend than water controls but did not differentiate between the low and high concentrations. Conversely, laboratory Cx. quinquefasciatus only preferred the high concentration to the low concentration. No statistical associations between oviposition preference and larval survival were found, as the chemical blend did not affect survivorship of either species.

4. The oviposition preference for the chemical blend over water controls suggests that both species oviposit in the best available resource environment, but further studies are needed before conclusions regarding preference–performance relationships can be drawn.

5. It was found that long-term laboratory colonisation affects the oviposition behaviour in Cx. quinquefasciatus, suggesting that behavioural studies on laboratory strains are not always applicable to wild populations.

2. In the present study, the potential trade-offs between total- and active phenoloxidase (PO), body size and body pigmentation in Sepsis thoracica black scavenger flies that show alternative male morphs differing in cuticular pigmentation, and body size were evaluated.

3. As expected, small/dark (obsidian) males showed higher total-PO activity than larger/orange (amber) males. A negative relationship was found between total-PO activity and body size in females and obsidian but not amber males, suggesting that growth and immunity are more costly for the former. In contrast, density did not affect PO activity, as predicted by the density-dependent prophylaxis hypothesis, which had not been tested in dipterans before. However, rearing density did affect the body size negatively in females and amber but not obsidian males, showing that male morph is largely determined by condition-dependent plasticity rather than genes.

4. This study provides good evidence that trade-offs between different life-history traits can result in alternative resource allocation strategies, even within one species. These strategies can produce strikingly different alternative phenotypes, evincing that there is not only one optimal solution to address fitness optimisation.

• We found a male polymorphism in Sepsis thoracica, which is largely determined by condition-dependent plasticity rather than genes.
• The males' polymorphism involves a trade-off between body size and immunity.
• Contrary to the predictions of the density-dependent prophylaxis hypothesis, larval density did not affect the immune system activity of the individuals.

2. Males of the damselfly Lestes sponsa were used to investigate whether the allometric patterns of the length and width of the anal appendages, used for grasping the female prior to mating, corresponded to male mating success. Across a large latitudinal gradient, it was hypothesised that there is a larger investment in the grasping apparatus, i.e. a steeper allometric slope, following higher mating success.

3. Behavioural observations in field enclosures showed the highest mating success at high latitude, while there were no significant differences in mating success between the central and low latitudes. Positive allometry was found for the length of the anal appendages in high-latitude males, while central- and low-latitude males showed no significant regressions of the traits on body size.

4. These results partially support the hypothesis, as high-latitude, more successful males invested more in the length (but not the width) of the grasping apparatus than did central- and low-latitude males. Therefore, higher mating success might be facilitated by larger investment in armaments. Intraspecific studies on allometric patterns of traits that participate in mating success might offer new insights into the role of those traits in the reproductive behaviour of a species.

2. The explanation most likely relates to the need to find a suitable pupation substrate, especially in terms of shelter from predation, and given that many predators and parasitoids use host plants as prey-location cues, mortality probably decreases with distance from the host plant. Hence, remaining on the host includes a long-term risk, while moving away from the host introduces an increased risk during locomotion.

3. Bivoltine species that overwinter in the pupal stage produce two kinds of pupae; non-diapausing pupae from which adults emerge after 1–2 weeks, or diapausing pupae that overwinter with adults emerging after 8–10 months.

4. Given the hypothesis of distance-from-host-plant-related predation, this should select for phenotypic plasticity with larvae in the diapausing generation having a longer wandering phase than larvae under direct development, if there is a trade-off between mortality during the wandering phase and accumulated mortality during winter.

5. Here this prediction is tested by studying the duration of the wandering period in larvae of the partially bivoltine swallowtail butterfly, Papilio machaon, under both developmental pathways.

6. The results are in agreement with the predictions and show that the larval wandering phase is approximately twice as long under diapause development. The authors suggest that the longer duration of the wandering phase in the diapause generation is a general phenomenon in Lepidoptera.

• When fully grown, butterfly larvae enter a wandering phase and typically pupate at a distance from their host plant, probably because mortality from predation decreases with distance from the host.
• The duration of the wandering phase is probably a trade-off between mortality during wandering and mortality during the pupal period, giving more weight to reducing pupal mortality in overwintering generations.
• In accordance with theory, we show that larvae wander for longer in diapausing, overwintering, generations compared with directly developing, summer, generations of the bivoltine European swallowtail butterfly, Papilio machaon.