Biological control by conservation of native natural enemies can, at its best, reduce the need for pesticides and prevent detrimental effects upon the environment. The present study investigated the role of ground-active generalist predators as natural enemies of two tortricid pests in apple orchards.

Predation rates were compared on the well established codling moth Cydia pomonella and the emerging oriental fruit moth Grapholita molesta, which has recently switched hosts to apples.

The present study hypothesized that the ground-active predators consumed the two tortricid pests in significant numbers without preference, and attacked the pests at different developmental stages.

Using diagnostic polymerase chain reaction on the gut contents of field-caught ground-active predators, no difference in predation rates was found on these two pests. Spiders were the most efficient predators of emergent adult moths in spring, whereas the carabid beetles, feeding on diapausing larvae, were important in the autumn.

The temporal complementarity between spiders and carabid beetles, attacking different stages of the pests at different times of year, highlights the need for diverse predator assemblages to optimize biological control.

Eriophyoid mites are among the most ubiquitous gall-inducing arthropods, and are adapted species-specifically to a broad diversity of plants, although their life histories remain poorly studied outside agricultural systems.

We examined the seasonal phenology of a leaf-galling eriophyid mite, the maple spindle gall mite Vasates aceriscrumena (MSGM), in naturally occurring stands of sugar maple Acer saccharum in south-central Ontario in 2007 and 2008.

Galls were first induced in spring (mid-May) and were devoid of mites by late August. In the study region, MSGM appears to have at least two generations, with overwintering, deutogyne females that initiate galls in spring (mid-May) after leaf flush, giving rise to a generation of protogyne (primary) females and a few morphologically similar males (<1 for every 10 females) and, subsequently, to a new generation of deutogyne females in mid-July to early August. In July, some galls can be highly crowded, with 50–200 individuals per gall.

In addition, a tarsonemid mite, Tarsonemus acerbilis, was found in approximately 40% of MSGM galls examined. As much as 95.4% of galls in 2007 and 97.4% in 2008 that contained tarsonemid larvae did not contain MSGM eggs (by contrast, only 2.3% of tarsonemid-free galls contained no MSGM eggs), suggesting that these juveniles feed, at least opportunistically, on MSGM eggs.

Gall ostiole morphology appeared to influence both MSGM and Tarsonemus densities within galls, with ‘open’ ostioles (versus ‘closed’) being much more susceptible to invasion by the tarsonemid. The latter is likely to be an important regulator of MSGM populations. We hypothesize that the two ostiole types are the result of selection pressures on the gall inducer, favouring closed gall entrances for increased protection, and possibly also on the host tree, favouring open galls to increase predator access.

Bark beetles are significant mortality agents of conifers. Four beetle species, the pine engraver Ips pini, the six-spined pine engraver Ips calligraphus sub. ponderosae, the southern pine beetle Dendroctonus frontalis, and the western pine beetle Dendroctonus brevicomis, cohabitate pines in Arizona.

A pheromone trapping study in ponderosa forests of Arizona determined the attraction of beetles to conspecific and heterospecific pheromone components in the presence and absence of host volatiles, and tested whether predators differ in their attraction to combinations of pheromone components and tree monoterpenes.

All four bark beetle species differed in their responses to heterospecific lures and monoterpenes. Ips calligraphus was the only species that increased in trap catches when heterospecific lures were added. Heterospecific lures did not inhibit the attraction of either Dendroctonus or Ips species. The replacement of myrcene with α-pinene increased the attraction of Dendroctonus, whereas the addition of α-pinene had mixed results for Ips. The prominent predators Temnochila chlorodia and Enoclerus lecontei were more attracted to the I. pini lure than the D. brevicomis lure, and the combination of the two lures with α-pinene was most attractive to both predator species.

Cross attraction and limited inhibition of bark beetles to heterospecific pheromones suggest that some of these species might use heterospecific compounds to increase successful location and colonization of trees. Predator responses to treatments suggest that tree volatiles are used to locate potential prey and predators are more responsive to Ips than to Dendroctonus pheromone components in Arizona.

We investigated how modifications in winter and spring temperature conditions may affect the survival of a spring-hatching Lepidoptera, the oak processionary moth Thaumetopoea processionea.

Supercooling and chilling injury experiments indicate that eggs are especially cold hardy at the start of the winter period, although this ability is reduced later in the season. In the spring, young larvae are sufficiently cold hardy to ensure no direct mortality as a result of late frosts.

A comparison of phenological models shows that neonate larvae may await the unfolding of new oak leaves for relatively long periods (e.g. 1–30 days). Under both low (4°C after 5 days at 16°C) and high temperature experimental scenarios (constant 16°C), the majority of neonate larvae can survive starvation for more than 2 weeks.

Larvae may also suffer from food depletion once their development has been initiated (e.g. during cold springs) if the threshold temperature for feeding is not reached for several consecutive days, or in the case of late frosts affecting foliage availability. When temperature is reduced to 4°C, developing larvae become inactive and do not feed anymore; their starvation survival capability is reduced to approximately 2 weeks (cold spring hypothesis). At 16°C, developing larvae that are deprived of food can only survive for 10 days (late frost hypothesis).

We conclude that, in the oak processionary moth, neonate larvae are relatively well adapted to early hatching relative to budburst, ensuring them the highest foliage quality for development. In some years, however, phenological asynchrony or cold spring conditions may affect the persistence of populations at the limits of the species' range.

The polyphagous European grapevine moth Lobesia botrana (Den. & Schiff.) is the principal native pest of grape berries in the Palearctic region. It was found in Napa County, California, in 2009, and it has subsequently been recorded in an additional nine counties, despite an ongoing eradication programme. The present study aimed to assess prospectively its potential geographical distribution and relative abundance in California and the continental U.S.A. A subsidiary goal was to provide explanation for timing control measures.

Data from the European literature were used to formulate and parameterize a holistic physiologically-based demographic model for L. botrana. This model was linked to an extant mechanistic model of grapevine phenology, growth and development that provides the bottom-up effects of fruiting phenology, age and abundance on L. botrana dynamics. Fruit age affects larval developmental rates, and has carryover effects on pupal development and adult fecundity. Also included in the model were the effects of temperature on developmental, survival and fecundity rates.

Observed daily weather data were used to simulate the potential distribution of the moth in California, and the continental U.S.A. The relative total number of pupae per vine per year was used as the metric of favourability at all locations. The simulation data were mapped using grass gis (http://grass.osgeo.org/).

The model predicts L. botrana can spread statewide with the highest populations expected in the hotter regions of southern California and the lower half of the Central Valley. In the U.S.A., areas of highest favourability include south Texas, and much of the southeast U.S.A.

The effects of a warmer climate on pest abundance were explored by increasing observed mean temperatures 2° and 3 °C. L. botrana abundance is expected to increase in northern California and in the agriculturally rich Central Valley but to decrease in the hot deserts of southern California where summer temperatures would approach its upper thermal limit.

Analysis of the timing of mating disruption pheromone for control of L. botrana suggests the greatest benefit would accrue by targeting adults emerging from winter diapause pupae and the flight of first summer adults.

This study reports the results obtained in an investigation of the putatively parthenogenetic aphid species Tuberolachnus salignus Gmelin. Tuberolachnus salignus is one of the largest aphid species in the world but where and how it overwinters is not known. It has recently become noteworthy because it is increasingly found on commercially grown willows used in bioenergy production.

Seven newly-developed polymorphic microsatellite markers were used to investigate the genetic diversity of the species, and also to confirm its reproduction strategy.

Tuberolachnus salignus shows very low clonal diversity; only 16 genotypes were found in 660 specimens from 27 populations in five countries.

There was limited geographical structuring in the samples, although the two most common genotypes, which comprised more than half of the specimens collected, had a very wide distribution.

Furthermore, we determined that these aphids, which live in very dense colonies, can consist of more than one genotype, suggesting aggregation of colonizing T. salignus. These results confirm the parthenogenetic nature of T. salignus and demonstrate the presence of common genotypes that are widespread in time and space.

The plant stress, plant vigour and pulsed stress hypotheses describe the relationships between drought stress, plant quality and herbivore performance. We used an aphid-Brassica system to test these hypotheses under different drought treatments.

The quantity of water added per plant/week was 75%, 50% and 25% of the control (unstressed) water regime for low, medium and high drought stress, respectively, and 50% applied fortnightly for pulsed drought stress. The performance of a ‘senescence’ (generalist) and a ‘flush’ feeder (specialist) aphid species and host plant quality were assessed.

Drought treatments had a similar effect on the fecundity and intrinsic rate of increase of both aphid species. Aphid performance on unstressed and highly drought-stressed plants was significantly lower compared with medium drought stress. On average, 20% greater fecundity and 40% greater intrinsic rates of increase were recorded for both aphid species at medium drought stress compared with unstressed plants.

Plant biomass and relative water contents were significantly greater for unstressed plants compared with high and pulsed drought treatments. Foliar nitrogen concentration was significantly greater in the high drought stress and pulsed treatments, and the dominant glucosinolate (glucobrassicin) concentration was significantly greater in drought stress treatments.

The present study supports the plant stress hypothesis, although the plant vigour and pulsed stress hypotheses are not supported by our data. The implications of these findings for plant–herbivore interactions under changing environmental conditions are discussed.

Aphid population dynamics in crops are often driven by interactions with their host plants, which can be extensively influenced by environmental change. Protective environments (i.e. plastic tunnels) are now frequently used for soft fruit production, which may affect the localized climate and alter such interactions. This two year study on red raspberry (Rubus idaeus) addressed how protected environments affected two aphid species; the large raspberry aphid Amphorophora idaei (LRA) and the small raspberry aphid Aphis idaei (SRA).

Temperatures were higher (up to 7–10 °C) in tunnels compared with the field. Plants in tunnels grew approximately 1.4 cm/week faster and had lower (approximately 35%) foliar amino acid concentrations than plants in the field.

Aphids affected plant growth differently depending on growing environment; they promoted plant growth by 18–37% in tunnels, although they had no such effect in the field. Aphids reduced total and essential amino acid concentrations, with SRA causing greatest reductions (approximately 40% and 33%, respectively).

Aphid population sizes were similar in both environments, although individual LRA were smaller in tunnels (30% smaller in 2007) compared with those in the field. We suggest that faster aphid development rates inside warmer tunnels were not realized as a result of the variable effects of the growing environment on amino acid composition.

We conclude that the increasing use of protected environments in crop production will not necessarily cause predictable increases in aphid populations, although it may alter aphid–plant interactions in terms of aphid-induced changes to plant growth.

Sirex noctilio is a woodwasp native to Eurasia and Northern Africa and has recently been found infesting pines in eastern North America. Its pest status in this new range is not yet known, although it is an important pest in other areas where it has been introduced. Pinus spp. in North America are hosts to several native and alien species of subcortical insects. Interactions between the woodwasp and these species may influence its distribution or the characteristics of its life history, thus affecting its population dynamics over time.

Sixty S. noctilio-infested Pinus spp. were felled in Ontario, Canada, and all phloem-feeding and woodboring insects were collected and identified from each 1-m section of the tree.

Sirex noctilio was in a tree alone 10% of the time but commonly shared the tree with subcortical beetles, such as Tomicus piniperda, Pissodes nemorensis, Ips grandicollis, Gnathotrichus materiarius and Monochamus carolinensis. The woodwasp was distributed throughout the tree stem and this distribution overlapped with that of the beetles.

Fewer but larger S. noctilio males emerged from trees with beetles compared with those without, although there was no statistical difference in females.

These findings suggest that co-habiting beetles could negatively affect S. noctilio population dynamics over time. The potential mechanisms for this interaction are discussed.

Preliminary investigations were carried out on Dryocosmus kuriphilus Yasumatsu on Castanea sativa Miller in Tuscany to assess variations in gall characteristics in coppice and high forest at two crown heights (height < 2 or 2–6 m), influence of bud size and bud position on oviposition rates and susceptibility of three cultivars.

Gall size may depend on various factors, including wasp population density. In the present study area, small galls (with one or two cells) were the most numerous in 2008, whereas larger galls (with more than three cells) prevailed in 2009.

Dryocosmus kuriphilus oviposition occurrence was influenced by both bud size and bud position. Buds with eggs tended to be larger in size compared with bud without eggs, suggesting that D. kuriphilus females prefer to lay eggs in larger buds (approximately 6 mm³) compared with smaller buds (approximately 3 mm³). The mean number of eggs per bud tended to decrease from the apical bud toward the basal bud.

Three C. sativa cultivars, Carpinese, Fusca and Cesurone, were examined. Fusca grafts had significantly more galls compared with Carpinese and Cesurone, whereas Cesurone grafts had more larvae per bud compared with Carpinese and Fusca. Overall, the Carpinese cultivar may be less susceptible to D. kuriphilus galling compared with the Fusca and Cesurone cultivars.

The oak processionary moth Thaumetopoea processionea (Notodontidae) is presently distributed in almost all European countries and in part of the Middle East. In the North, its range limit passes through the Netherlands and Germany, and the southern part of Poland and Ukraine. In the South, the species is present in all the countries located on the northern shore of the Mediterranean Sea, in Anatolia, and in the mountains surrounding the Dead Sea Transform.

Using information from museum and personal collections, the available literature and other relevant datasets, we show that the species was already largely distributed throughout Europe before 1920. The available data do not provide any evidence of any long-term latitudinal shift of the species betwen 1750 and 2010.

In the northernmost part of its range, the population dynamics of the species is characterized by important fluctuations. We studied their pattern in Belgium, the Netherlands and part of Germany, after the apparent regional disappearance of the species during the first half of the 20th Century. The data suggest a continuous extent of the apparent distribution of the insect between 1970 and 2009, at a rate of approximately 7.5 km per year.

To explain the present distribution of the species, we discuss possible improvements of environmental conditions that could have triggered local population increases and favoured dispersal to adjacent areas. In addition, human activity, including the commercial movements of infested nursery trees, was recently suspected to be another source of spread over geographical barriers.

Individual mark–release–recapture is an important method for gathering data on insect movement, although it is limited by the constraints of tagging small insects with individual information.

Microdots, originally developed for covert security applications, are small polymer discs (diameter 0.5 mm) bearing up to 26 characters of information and have the potential as an alternative to the larger bee tags. In the present study, we test microdots for the individual marking of a 9-mm parasitoid wasp.

We individually marked 505 wasps. The recapture rate was 24% of individuals over 189 recapture events, for which 84% retained legible microdot labels. Movement was in the range 0–161 m with a mean displacement 21.2 ± 2.7 m. A captive survival experiment showed no difference in lifespan between marked and unmarked wasps.

The present study shows that microdots can provide an effective, durable, low-cost method for individually tagging small insects. The technique offers new opportunities by greatly expanding the capability for individually marking small insects, shifting the minimum size below that of bee tags, which is the only other manufactured option for individualized miniature marking.

The sustainable use of forest resources requires an understanding of the influence of site conditions and forest health on both pest species and those species providing ecosystem services such as pollination and decomposition.

The beetle family Cerambycidae is diverse and contains both pest and nonpest species, with many species performing such ecosystem services.

We predicted that as hardwood tree productivity decreased, the proportion of pest Cerambycidae present would increase at a site. We used site index as a measure of hardwood tree productivity.

The proportion of species that were pests did not change with productivity because the abundance of both pest and nonpest species increased with declining productivity.

The findings of the present study have implications for both managing pest species and conserving the biodiversity of nonpest species.

The vine weevil Otiorhynchus sulcatus is a major pest of horticultural crops worldwide, with root-feeding larvae causing most damage. Adult oviposition aboveground may therefore influence levels of damage as the larvae are relatively immobile after oviposition.

The present study investigated feeding and oviposition behaviour on red raspberry Rubus idaeus using intact plants, ensuring that choices reflected the realistic differences in cultivar appearance and chemical composition. Previous studies investigating vine weevil feeding and oviposition on other crops have used excised plant material, which may inadvertently influence behaviour.

Adult weevils significantly preferred to feed on particular cultivars in the choice experiment (e.g. Tulameen), although they consumed significantly more foliage (0.22–1.03 cm²/day) on different raspberry cultivars (e.g. Glen Moy, Glen Rosa and a wild accession) in no-choice situations.

In choice experiments, weevils tended to avoid laying eggs on some cultivars (e.g. Glen Moy and the wild accession). The number of eggs laid (1.91–4.32 eggs per day) did not, however, differ significantly between the cultivars in a no-choice situation. Foliar nitrogen and magnesium concentrations were positively, although weakly, correlated with the total number of eggs laid.

The present study highlights the importance of considering both choice and no-choice tests when assessing crop susceptibility to attack because weevils may avoid feeding on certain cultivars (e.g. Glen Moy) when given a choice, although this would cause significant damage to such cultivars if they were grown in monoculture (i.e. when there is no alternative).

Invertebrate pests, such as blue oat mites Penthaleus spp., cause significant economic damage to agricultural crops in Australia. Climate is a major driver of invertebrate species distributions and climate change is expected to shift pest assemblages and pest prevalence across Australia. At this stage, little is known of how individual species will respond to climate change.

We have mapped the current distribution for each of the three pest Penthaleus spp. in Australia and built ecological niche models for each species using the correlative modelling software, maxent. Predictor variables useful for describing the climate space of each species were determined and the models were projected into a range of future climate change scenarios to assess how climate change may alter species-specific distribution patterns in Australia.

The distributions of the three cryptic Penthaleus spp. are best described with different sets of climatic variables. Suitable climate space for all species decreases under the climate change scenarios investigated in the present study. The models also indicate that the assemblage of Penthaleus spp. is likely to change across Australia, particularly in Western Australia, South Australia and Victoria.

These results show the distributions of the three Penthaleus spp. are correlated with different climatic variables, and that regional control of mite pests is likely to change in the future. A further understanding of ecological and physiological processes that may influence the distribution and pest status of mites is required.

The pecan nut casebearer Acrobasis nuxvorella Neunzig (Lepidoptera: Pyralidae) is an important, monophagous pest of pecan Carya illinoinensis (Fagales: Juglandaceae).

This pest is native from Louisiana west to the eastern edge of New Mexico and north to Illinois in the U.S.A. and as far west as Chihuahua and south to Oaxaca in Mexico.

Recently, this pest has expanded beyond the native range of pecan into regions where pecan has been introduced for cultivation.

Amplified fragment length polymorphism markers were used to determine the population genetic structure of this insect pest across its current geographical distribution.

Population genetic analyses indicate a great degree of genetic structure in the pecan nut casebearer across its geographical distribution, with genetically distinct populations occurring in those areas where the pecan nut casebearer is not native but has been invasive.

The rice leaffolder Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae) is a serious rice pest in Asia. The conspicuous foliar damage caused by C. medinalis larvae leads to early-season insecticide applications that disrupt the biological control of this and other pest species.

Despite the often dramatic impact of C. medinalis, rice plants can tolerate severe defoliation with no impact on grain yield, although persuading farmers to withhold insecticide application has proven very difficult.

The present review assesses the prevention of damage caused by C. medinalis via biological control using parasitoids. Information on the indigenous parasitoids of C. medinalis is drawn together for the first time from the non-English literature published in Asia. This is integrated with the wider English language literature to provide a comprehensive analysis of the parasitoid fauna.

Survey studies have been conducted in many Asian countries in recent decades, showing that parasitoids of rice pests can achieve high rates of parasitism but are far from consistent as a mortality factor. There is much less work available on the biology of leaffolder parasitoids in rice and there is an unexpected dearth of studies regarding increasing their performance by providing nectar sources, which is a widely explored approach for other crop systems.

It is concluded that the recently reported work in which nectar plants are established on rice bunds to support planthopper parasitoids may have significant benefit for leaffolder parasitoids. The use of plant species, however, that are selective in not allowing adult moths to feed will be essential.

Insect pests, biological invasions and climate change are considered to represent major threats to biodiversity, ecosystem functioning, agriculture and forestry. Deriving hypothesis of contemporary and/or future potential distributions of insect pests and invasive species is becoming an important tool for predicting the spatial structure of potential threats.

The western corn rootworm (WCR) Diabrotica virgifera virgifera LeConte is a pest of maize in North America that has invaded Europe in recent years, resulting in economic costs in terms of maize yields in both continents. The present study aimed to estimate the dynamics of potential areas of invasion by the WCR under a climate change scenario in the Northern Hemisphere. The areas at risk under this scenario were assessed by comparing, using complementary approaches, the spatial projections of current and future areas of climatic favourability of the WCR. Spatial hypothesis were generated with respect to the presence records in the native range of the WCR and physiological thresholds from previous empirical studies.

We used a previously developed protocol specifically designed to estimate the climatic favourability of the WCR. We selected the most biologically relevant climatic predictors and then used multidimensional envelope (MDE) and Mahalanobis distances (MD) approaches to derive potential distributions for current and future climatic conditions.

The results obtained showed a northward advancement of the upper physiological limit as a result of climate change, which might increase the strength of outbreaks at higher latitudes. In addition, both MDE and MD outputs predict the stability of climatic favourability for the WCR in the core of the already invaded area in Europe, which suggests that this zone would continue to experience damage from this pest in Europe.

The disruption of host-finding cues has been proposed as a key mechanism underlying the lower damage caused by phytophagous insects in mixed forests. We tested this hypothesis by investigating the distribution of pine processionary moth Thaumetopoea pityocampa (Denis & Schiffer-Müller) (Lepidoptera) infestation at the edges of pure stands of Pinus pinaster (AÏton) at some distance from nonhost trees (Experiment 1) or bordered in part by a broadleaved hedgerow (Experiment 2).

An ‘edge effect' was demonstrated, with trees at the edge of the stand being more heavily infested than those at the interior of the stand.

The presence of a nonhost broadleaved hedgerow in front of the edge of the pine stand resulted in lower T. pityocampa infestation. There were significantly fewer T. pityocampa nests behind the hedgerow than on the exposed part of the edge. The presence of the hedgerow did not dilute or repel T. pityocampa infestation further into the pine stand, although it decreased the infestation of T. pityocampa throughout the pine stand. The decrease in T. pityocampa infestation behind the hedgerow was greater when the broadleaved hedgerow was taller than the pine trees.

These results highlight the benefits of using nonhost tree species on the edge of monospecific forest stands to reduce insect damage. This approach could be promoted as an innovative forest pest management method.

The importance of nutrients consumed by adults differs among lepidopteran species. Knowledge of adult nutritional requirements is particularly useful when adopting biological control strategies that involve the use of flowering plants to improve the effectiveness of natural enemies. This is because nectar may also serve as a carbohydrate source for the pest.

We evaluated the effect of different sources and concentrations of carbohydrate consumed by adults on the performance and fitness of the wheat armyworm Pseudaletia sequax Franclemont, which is an important pest of cereal crops.

The consumption of carbohydrates by the adults significantly increased the length of the oviposition period, fecundity, fertility and longevity of P. sequax. Adult nutrition also affected the daily oviposition pattern of the females.

The demographic parameters estimated for each diet regime (i.e. intrinsic rate of increase, finite rate of increase and net reproductive rate) were influenced by adult nutrition. These parameters also varied according to the source and concentration of carbohydrates.

The results obtained in the present study suggest that the use of perennial flowering plants to provide a food source for natural enemies can also favour the pest.

The development of integrated pest management strategies requires that the semi-natural habitats scattered across the landscape are taken into account. Particular determinants of insect pest abundance in overwintering habitats just before they migrate onto crops appear to be poorly known and of crucial importance for understanding patterns of crop colonization and pest population dynamics at the landscape scale.

The emergence of pollen beetle Meligethes aeneus F. was studied in grassland, woodland edge and woodland interior over a 3-year survey in France using macro-emergence traps. A suite of variables at the local and the landscape scale was assessed for each trap, aiming to identify potential relevant habitat indicators. The effects of habitat characteristics were evaluated using partial least square regressions.

It was found that M. aeneus can overwinter in all types of habitat but that particular habitat characteristics at the local and landscape scales may explain their abundance in overwintering sites more than the types of habitat: relative altitude, litter thickness, soil moisture and proximity to the previous year's oilseed rape fields appear to be positively correlated with abundance of adults over the 3 years.

Hence, the abundance of emerged pollen beetles depends on both the landscape configuration of the previous year's oilseed rape fields around overwintering sites and local habitat characteristics. Landscape configuration may determine population flow towards overwintering sites in the late summer, and local habitat characteristics may influence survival rates during the winter. The findings of the present study provide valuable insight into the role of semi-natural habitats as a source of pests, patterns of crop colonization in the spring, and the influence of landscape on pollen beetle abundance.

Ants are important generalist predators in most terrestrial ecosystems. However, because many ant species are also hemipteran mutualists, their role in agriculture has generally been considered to be negative for plants.

In the present study, we report an experiment in ant-exclusion from tree canopies in an organic citrus grove with two main objectives: (i) to examine whether the absence of ants increased the abundance of some beneficial arthropods and reduced the attack of some pests such as aphids and (ii) to examine whether ant-exclusion increased the fruit yield of citrus trees.

The exclusion of ants from tree canopies had positive effects on the arthropod assemblage and on fruit yield. However, the 8-year duration of the experiment can be divided into two periods with contrasting results. In the first period, the arthropod assemblage was only slightly affected, except for a greater density of aphids in ant-excluded trees; in addition, fruit yield was higher in ant-excluded trees than in the control ones. In the second period, ant-exclusion increased the abundance of most arthropod groups, although the previous positive effect on fruit yield was no longer observed.

There are two main conclusions of the present study. First, from an applied perspective, ant-exclusion from tree canopies is not a sound management alternative in citrus plantations in the Mediterranean. Second, the 8-year duration of the experiment highlighted the importance of long-term experiments in community ecology and biological control because the effects observed in the first 4 years of the experiment were very different from what occurred subsequently.

Although the successful management of the Colorado potato beetle Leptinotarsa decemlineata (Say) depends on the prevention of its dispersal, its walking pattern in the landscape remains poorly understood. In the present study, post-diapause, early summer, late summer and colony adult beetles, both fed and unfed before release, were tracked with a harmonic radar to establish their walking movement pattern in a bare-ground field.

The random walk model successfully described the dispersal of all beetle types, whether fed or unfed.

The diverse life history of this species was manifested by an increased distance travelled and deviations of individual paths from the random model. Starved post-diapause beetles travelled furthest and individual paths deviating from random were both local and directed, probably aiming to maximize opportunities for host colonization. Starved early summer beetles also travelled further than fed beetles but relied more on random movement to disperse in the habitat. Starving had little impact on the distance travelled or the path deviations of late summer beetles that are searching for overwintering site rather than hosts.

The increased displacement of starving beetles over fed beetles corresponded with an increased walking step and index of straightness.

The impact of starvation on travel distance was greater than expected from laboratory tests.

In conclusion, the results obtained in the present study suggest a random walking pattern to search arable land until host volatile or visual impulses trigger a more directed walk or flight.

Aphids, similar to all insects, are ectothermic and, consequently, are greatly affected by environmental conditions. The peach potato aphid Myzus persicae (Sulzer) has a global distribution, although it is not known whether populations display regional adaptations to distinct climatic zones along its distribution and vary in their ability to withstand and acclimate to temperature extremes. In the present study, lethal temperatures were measured in nine anholocyclic clones of M. persicae collected along a latitudinal cline of its European distribution from Sweden to Spain. The effects of collection origin and intra- and intergenerational acclimation on cold and heat tolerance, as determined by upper and lower lethal temperatures (ULT₅₀ and LLT₅₀, respectively), were investigated.

Lethal temperatures of M. persicae were shown to be plastic and could be altered after acclimation over just one generation. Lower lethal temperatures were significantly depressed in eight of nine clones after acclimation for one generation at 10°C (range: −13.3 to −16.2°C) and raised after acclimation at 25°C (range: −10.7 to −11.6°C) compared with constant 20°C (range: −11.9 to −12.9°C). Upper lethal temperatures were less plastic, although significantly increased after one generation at 25°C (range: 41.8–42.4°C) and in five of nine clones after acclimation at 10°C. There was no evidence of intergenerational acclimation over three generations.

Thermal tolerance ranges were expanded after acclimation at 10 and 25°C compared with constant 20°C, resulting in aphids reared at 10°C surviving over a temperature range that was approximately 2–6°C greater than those reared at 25°C.

There was no clear relationship between lethal temperatures and latitude. Large scale mixing of clones may occur across Europe, thus limiting local adaption in thermal tolerance. Clonal type, as identified by microsatellite analysis, did show a relationship with thermal tolerance, notably with Type O clones being the most thermal tolerant. Clonal types may respond independently to climate change, affecting the relative proportions of clones within populations, with consequent implications for biodiversity and agriculture.

Declining numbers in honeybees and various wild bee species pose a threat to global pollination services. The identification and quantification of the pollination service provided by different taxa within the pollinator guild is a prerequisite for the successful establishment of nature conservation and crop management regimes.

Wild bees and hoverflies are considered to be valuable pollinators in agricultural and natural systems. Although some information on pollination efficiency of individual pollinator species is available, comparative studies of both taxa at different densities are rare. In the present study, the efficiency of the solitary mason bee Osmia rufa and two hoverfly species (Eristalis tenax and Episyrphus balteatus) as pollinators of oilseed rape Brassica napus was examined in a standardized caged plant breeding regime. Honeybee Apis mellifera colonies were used as a reference pollinator taxon.

Yield parameters responded differently to pollinator density and identity. Fruit set and number of seeds per pod increased with increasing pollinator density, although these were stronger in the mason bee than the hoverfly treatment. Weight per 1000 seeds did not respond to any pollinator treatment, indicating that seed quality was not affected. Oilseed rape yield in the highest tested densities of both pollinator taxa resulted in yield values close to the efficiency of small honeybee colonies.

Hoverflies required approximately five-fold densities of the red mason bees to reach a similar fruit set and yield. Thus, mason bees are more efficient in plant breeding and managed pollination systems. Both natural pollinator taxa, however, are of potential value in open and closed crop production systems.

Diversifying agricultural ecosystems to enhance biological control is a promising way of promoting sustainable pest management.

In the present study, monoculture apple and peach with standard insecticide treatments were compared with three biodiverse treatments (polyculure, monoculture with companion plants and polyculture with companion plants) with reduced standard insecticide use.

Abundance of insect predators was increased by both the presence of companion plants and extrafloral nectar but parasitism of the leafroller Platynota idaeusalis was not affected.

There were no consistent effects of biodiversity treatment on either tree growth or fruit yield. Insect injury to Empire apple and peach fruit was not consistently affected by the biodiversity treatments. Granny Smith apples were harvested later than Empire and had more fruit injury in the biodiverse treatments than the standard insecticide control.

A reduction in pesticides with added biodiversity proved to be a viable alternative to standard chemical insecticide management for temperate tree fruit. Increases in the natural control of pests resulting from increased plant diversity has promise for reducing the reliance on chemical insecticides for pest suppression.

Diachasmimorpha krausii is a braconid parasitoid of larval tephritid fruit flies, which feed cryptically within host fruit. At the ovipositor probing stage, the wasp cannot discriminate between hosts that are physiologically suitable or unsuitable for offspring development and must use other cues to locate suitable hosts.

To identify the cues used by the parasitoid to find suitable hosts, we offered, to free flying wasps, different combinations of three fruit fly species (Bactrocera tryoni, Bactrocera cacuminata, Bactrocera cucumis), different life stages of those flies (adults and larvae) and different host plants (Solanum lycopersicon, Solanum mauritianum, Cucurbita pepo). In the laboratory, the wasp will readily oviposit into larvae of all three flies but successfully develops only in B. tryoni. Bactrocera tryoni commonly infests S. lycopersicon (tomato), rarely S. mauritianum (wild tobacco) but never C. pepo (zucchini). The latter two plant species are common hosts for B. cacuminata and B. cucumis, respectively.

The parasitoid showed little or no response to uninfested plants of any of the test species. The presence of adult B. tryoni, however, increased parasitoid residency time on uninfested tomato.

When the three fruit types were all infested with larvae, parasitoid response was strongest to tomato, regardless of whether the larvae were physiologically suitable or unsuitable for offspring development. By contrast, zucchini was rarely visited by the wasp, even when infested with B. tryoni larvae.

Wild tobacco was infrequently visited when infested with B. cacuminata larvae but was more frequently visited, with greater parasitoid residency time and probing, when adult flies (either B. cacuminata or B. tryoni) were also present.

We conclude that herbivore-induced, nonspecific host fruit wound volatiles were the major cue used by foraging D. krausii. Although positive orientation to infested host plants is well known from previous studies on opiine braconids, the failure of the wasp to orientate to some plants even when infested with physiologically suitable larvae, and the secondary role played by adult fruit flies in wasp host searching, are newly-identified mechanisms that may aid parasitoid host location in environments where both physiologically suitable and unsuitable hosts occur.

Bark beetles (Coleoptera: Curculionidae, Scolytinae) are commonly recognized as important tree mortality agents in coniferous forests of the western U.S.A.

High stand density is consistently associated with bark beetle infestations in western coniferous forests, and therefore thinning has long been advocated as a preventive measure to alleviate or reduce the amount of bark beetle-caused tree mortality.

The present study aimed to determine the effectiveness of thinning to reduce stand susceptibility to bark beetle infestations over a 10-year period in Pinus jeffreyi forests on the Tahoe National Forest, California, U.S.A. Four treatments were replicated three times within 1-ha square experimental plots. Treatments included thinning from below (i.e. initiating in the smallest diameter classes) to a residual target basal area (cross-sectional area of trees at 1.37 m in height) of: (i) 18.4 m²/ha (low density thin); (ii) 27.6 m²/ha (medium density thin); (iii) 41.3 m²/ha (high density thin); and (iv) no stand manipulation (untreated control).

Throughout the present study, 107 trees died as a result of bark beetle attacks. Of these, 71% (75 trees) were Abies concolor killed by Scolytus ventralis; 20.6% (22 trees) were Pinus ponderosa killed by Dendroctonus ponderosae; 4.7% (five trees) were P. jeffreyi killed by Dendroctonus jeffreyi; 1.8% (two trees) were P. jeffreyi killed by Ips pini; 0.9% (one tree) were P. jeffreyi killed by Orthotomicus (= Ips) latidens; 0.9% (one tree) were P. ponderosa killed by both Dendroctonus brevicomis and D. ponderosae; and 0.9% (one tree) were P. jeffreyi killed by unknown causes.

In the low density thin, no pines were killed by bark beetles during the 10-year period. Significantly fewer trees (per ha/year) were killed in the low density thin than the high density thin or untreated control. No significant treatment effect was observed for the percentage of trees (per year) killed by bark beetles.