• conservation biological control;
  • Fagopyrum esculentum;
  • HIPVs;
  • induced plant defence;
  • parasitoids;
  • volatiles


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

1. An increase in pesticide resistance in many pest species is promoting interest in biological control. Much remains to be learned about natural enemy immigration into and persistence within crops at specific times and how to maximize suppression of pest populations. Therefore this study was conducted to test a novel biological control approach, ‘attract and reward’ which combines two aspects of applied insect ecology: synthetic herbivore-induced plant volatiles (HIPVs) to improve immigration of beneficial taxa into crops and nectar plants to maintain their populations.

2. The ‘attract and reward’ approach was tested in sweetcorn, broccoli and wine-grapes with several HIPV formulations at 1·0% (v/v) as attractants and buckwheat (Fagopyrum esculentum Moench) as reward. Abundance of insects was assessed with non-attractive sticky traps for up to 22 days after the HIPV spray application.

3. In sweetcorn, Eulophidae were more numerous in the attract treatments: methyl anthranilate, methyl jasmonate (MeJA), methyl salicylate (MeSA) and HIPV mix. Encyrtidae were more abundant near MeJA-treated plants. In broccoli, Scelionidae were more abundant in MeSA treatments with reward and near cis-3-hexenyl acetate-treated plants without reward whilst Ceraphronidae were more numerous near MeSA and predators were more abundant near HIPV mix-treated plants. Nectar plant reward increased catches of parasitoids from several families in all three tested crop species and increased predators in sweet corn and broccoli.

4. Increases in natural enemy numbers were correlated with effects at the first and second trophic levels. Significantly fewer larvae of the sweetcorn pest Helicoverpa spp. were found on sweetcorn plants from plots with reward and significantly less Helicoverpa spp. damage was evident to cobs for one of the HIPV treatments.

5.Synthesis and applications. Results suggest that applications of synthetic HIPVs can enhance recruitment of natural enemies and buckwheat was a suitable resource subsidy plant for increasing abundance and residency. Whilst both of these approaches offer potential to enhance biological control, further work is required to realize fully synergistic effects from their combination as an ‘attract and reward’ approach.


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Pest control in modern agro-ecosystems is largely achieved by using pesticides and such reliance has led globally to the development of pesticide resistance in many crop pests (Whalon, Mota-Sanchez & Hollingworth 2008). The rising costs of pesticides, a decreasing range of available pesticides and increased consumer awareness of the presence on fresh produce of pesticides residues have led to pest control by natural enemies becoming an attractive alternative (Bostanian et al. 2004). Conservation biological control (CBC) involves cultural practices that seek both to preserve natural enemy populations and to improve their efficacy through modification of the biotic environment and reducing pesticide usage (Landis, Wratten & Gurr 2000). Research on CBC aims to improve the reliability of biological control by increasing the abundance and diversity of natural enemies in crops and hence their parasitism and predation of crop pests. Habitat manipulation, a CBC method, may achieve this aim and can be applied within the crop, or at the farm or landscape level (Gurr, Wratten & Altieri 2004). It involves diversifying agro-ecosystems by integrating plant species whose flowers provide suitable nectar or pollen and shelter (Landis, Wratten & Gurr 2000). Laboratory and field studies have established that many adult hymenopteran parasitoids benefit from floral foods by increased longevity and fecundity and, for some parasitoids, such feeding is essential for egg maturation (Jervis et al. 1993; Baggen, Gurr & Meats 1999; Winkler et al. 2009). Numerous habitat manipulation studies that integrated different flowering plants within crops have demonstrated the potential and practicality of this pest control tactic (Baggen & Gurr 1998; Bostanian et al. 2004; Lee & Heimpel 2005; Irvin et al. 2006). Other studies, however, found no clear benefits from the integration of flowering resources (Berndt, Wratten & Hassan 2002; Bone et al. 2009).

Another, more novel CBC method that can increase natural enemy abundance in crops involves the use of synthetic herbivore-induced plant volatiles (HIPVs) which attract natural enemies into crops from surrounding habitats. Plants respond to herbivore damage, as a form of induced direct and indirect defence, by producing volatile signalling compounds also termed semiochemicals (Dicke et al. 1990). Parasitoids or predators of the attacking herbivore use these HIPVs to orientate themselves to their host or prey (Karban & Baldwin 1997). Many crop plants have been reported to emit HIPV blends in response to herbivore damage (Dicke 1999) with some compounds, including methyl salicylate (MeSA), methyl jasmonate (MeJA), cis-3-hexenyl acetate (HA) and cis-hexen-1-ol, occurring commonly across different blends (Paré & Tumlinson 1999; Van Den Boom et al. 2004). The attraction of natural enemies by synthetic HIPVs has been demonstrated under laboratory and field conditions and their potential value in pest management has been recognized (Thaler 1999; James 2005; James & Grasswitz 2005; Zhu & Park 2005; Yu et al. 2008; Orre et al. 2010).

Two main factors have been associated with the success of CBC of crop pests: (i) recruitment of beneficials early in the cropping season and (ii) retention of natural enemy populations throughout a crop’s life span (Khan et al. 2008).

Synthetic HIPVs can be used in a combined ‘attract and reward’ approach whereby they are deployed early in the cropping season or synchronized with the detection of pests. Natural enemies will be recruited at a time when establishment of floral groundcover within and/or around crops might reduce emigration and maximize performance of attracted natural enemies by providing food, shelter and alternative hosts or prey. Many beneficial parasitoids and predators have the ability to locate hosts and non-host foods using visual and olfactory cues (Wäckers & Lewis 1994) and need hosts, food and shelter for successful reproduction (Lewis et al. 1998). However, the use of HIPVs alone may not achieve consistent biological control success, and may even negatively influence natural enemies in low pest density situations. Combining HIPVs with floral resources may bridge this problem. We hypothesized that the ‘attract’ and ‘reward’ aspects would each result in higher abundance of natural enemies but that their combined use would be synergistic. Therefore we conducted three field experiments, one each in sweetcorn, broccoli and wine-grapes by deploying several synthetic HIPVs with and without reward plants to investigate attraction and retention of natural enemies by treated plants. The effects of treatments on pest numbers and crop yield and health were also assessed.

Materials and methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Three field experiments were conducted in the central west region of New South Wales (NSW), Australia in sweetcorn Zea mays L., broccoli Brassica oleracea L. and wine-grapes Vitis vinifera L. A two-factor randomized block design was used for all experiments with ‘attract’ (HIPVs) and ‘reward’ (buckwheat) as factors. In each field experiment, there were four replications with a plot spacing of a least 15 m (James 2005) to minimize inter-plot interference.

Herbivore-induced plant volatiles

A canola oil-based formulation Synertrol® (Organic Crop Protectants Pty Ltd, Lilyfield, NSW, Australia) was enhanced with several synthetic HIPVs at 1·0% v/v. The formulations were diluted in water at 5 mL per 1 L and applied with a hand-sprayer to the foliage until runoff. An earlier study evaluated the efficacy of several synthetic HIPVs at three concentrations in the same crops to attract beneficial arthropods (Simpson et al. 2011). This work formed the basis for the HIPV compounds and dosage used for each of the experiments in this study. Additionally, a HIPV mix was included because plants emit HIPV blends in response to herbivorous damage (Yu et al. 2008). The HIPVs were spray-applied, because previous studies have demonstrated the success of this technique (James in press; Simpson et al. in press) and mechanization of the technique is advantageous.


A floral reward strategy was used over artificial food supplements. This can increase the abundance of natural enemies but may need to be applied repeatedly. Buckwheat (cv. Ikeda) Fagopyrum esculentum Moench was chosen because previous studies have demonstrated that the incorporation of this plant within crops led to increased abundance and fitness of natural enemies, higher parasitism rates and lower pest abundance (Berndt, Wratten & Hassan 2002; Lavandero et al. 2005; Lee & Heimpel 2005; Begum et al. 2006; Irvin et al. 2006; Witting-Bissinger, Orr & Linker 2008). Buckwheat has quick germination and short sowing to flowering time (Bowie, Wratten & White 1995) which was of agronomic importance.

Sweetcorn experiment

The study site was located on a farm near the town of The Lagoon, NSW (33°32′51·84″ S, 149°36′51·27″ E). The experiment included four attract treatments: MeSA, MeJA, methyl anthranilate (MeA), a mix of MeSA, MeJA, MeA (each HIPV was added to Synertrol® equally making a 1·0% formulation) and a water control, each with and without buckwheat, giving 10 treatments in all. Each plot comprised an average of 12 sweetcorn plants in one row. Buckwheat was added to reward plots as a 1 × 2 m row immediately alongside the corn plants. Buckwheat seeds were hand-sown at 100 g per plot into cultivated ground on 27 November 2008, 1 day after the sweetcorn was sown. HIPV treatments were spray-applied to sweetcorn plants on 9 February 2009. At this stage, the buckwheat in all of the reward plots was in bloom and the sweetcorn was at silking growth stage, a critical phase for Helicoverpa spp. larvae attack. Insects abundance was measured with non-attractive sticky traps (21 × 14·9 cm, two traps per treatment plot), made of clear acetate sheets coated with clear insect trapping adhesive (The Tanglefoot Company®, Grand Rapids, MI, USA). Traps were located within 15 cm of the sweetcorn plants to the side of the buckwheat and were replaced on days 1, 4, 10, 18 and 22 after spraying. Trapped insects were examined with a dissecting microscope and identified using Naumann (1991) and Stevens et al. (2007). A diverse range of natural enemies and pest taxa were counted. One day after the HIPV spray application, Helicoverpa spp. larvae were counted from all sweetcorn plants in each plot to determine the effect of buckwheat prior to the HIPV application. On 3 March 2009 the cobs of all treatments were harvested for assessment of yield, Helicoverpa spp. and rodent damage. Cobs from each treatment were bagged separately and stored in a rodent proof cool-room at 4 °C for 3 weeks until yield and damage were assessed.

Broccoli experiment

The study site was located on a farm near the town of Oberon, NSW (33°32′51·84″ S, 149°50′21·46″ E). The experiment included four attract treatments: MeSA, HA, benzaldehyde (Be) and a mix of MeSA, HA and Be (each HIPV was added equally to Synertrol® making a 2·0% formulation) and a water control, each with and without reward, giving 10 treatments in all. Each plot comprised four broccoli plants in one row. Buckwheat was established in the reward plots as a 0·60 × 2 m row immediately adjacent to the broccoli plants. Buckwheat seeds were hand-sown at 50 g per plot into cultivated ground on 15 January 2009 one day after the broccoli seedlings were planted. HIPV treatments were spray-applied to broccoli plants on 2 March 2009 when the buckwheat in all of the reward plots was in bloom. The broccoli plants were 6 weeks old and at the vegetative growth stage with sideshoots being developed. Two traps were located within 15 cm of the broccoli plants to the side of the buckwheat and replaced on days 2, 4, 11, 18 and 25 after spraying. Arthropod monitoring and identifications were as previously described. On 18 March 2009, all broccoli plants in each plot were examined for diamond back moth (DBM) Plutella xylostella Linnaeus (Lepidoptera: Tortricidae) larvae, a pest of brassicas. Diamond back moth larvae were collected and reared in the laboratory on broccoli leaves until emergence of adult moths or the parasitoid Diadegema semiclausum Hellén (Hymenoptera: Ichneumonidae) to determine parasitism rate.

Vineyard experiment

The study site was located in a cv. Merlot vineyard near the city of Orange, NSW (33°16′11·74″ S, 149°00′07·74″ E). The experiment included three attract treatments: MeSA, HA, MeA and a water control, each with and without reward, giving eight treatments in all. Each plot comprised five grapevines and buckwheat was added to the reward plots as areas of 1·5 × 5 m in the mid-row area either side of the grapevines. Buckwheat seeds were hand-sown at 200 g per plot into cultivated ground on 4 December 2008. HIPV treatments were spray-applied to grapevines when the buckwheat in all of the reward plots was in bloom. Grapevines were at bunch closure growth stage, a critical period for Epiphyas postvittana (Lepidoptera: Tortricidae) damage. HIPVs were spray-applied on 23 February 2009 which was repeated on 9 March 2009 due to low natural enemy abundance trapped on sticky traps collected 1 and 6 days after the first spray application. Two traps were attached to a wooden stake immediately after spraying within 15 cm of the grapevine foliage and replaced on days 1, 4 and 11 after the first spraying. Traps were replaced 1, 3, 13 and 20 days after the second spraying. Arthropod monitoring and identifications were as previously described.

Statistical analysis

GenStat 12th Edition (Payne et al. 2009) was used for data analysis. Insect data from sticky traps were converted to daily captures due to the uneven time periods of trap replacement. Raw data were square-root transformed √(x + 0·5) due to non-normal distribution and to ensure residuals were homogenous. Restricted maximum likelihood procedure was used for the analysis. Fixed terms were ‘attract’ (HIPV), ‘reward’ (buckwheat) and time to test for main effects and interactions and random terms were spatial coordinates. Treatment means within each significant factor and/or interactions were differentiated using the least significant difference (l.s.d.) at 5% generated from the repeated measures model. Canonical variate analysis was used to create two new variables from all families which best separated the treatments, the first two accounted for <60% of the treatment variation and therefore have not been reported on further.

Data on Helicoverpa larvae collected from sweetcorn plants, Helicoverpa and rodent damage in sweetcorn cobs were analysed using the restricted maximum likelihood procedure, to account for spatial variability. The same statistical model was used to analyse the proportion of parasitoids emerged from the collected DBM larvae from broccoli plants.


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Sweetcorn experiment

During the sampling period, 6360 individuals were trapped including 10 hymenopteran families, predators [Dicranolaius bellulus Guérin-Méneville (Coleoptera: Melyridae), Coccinellidae, lacewings (Neuroptera), Syrphidae, Araneae and predatory thrips (Thysanoptera: Aleolothripidae and Phlaeothripidae)], Diptera: Tachinidae, herbivorous Thysanoptera, adult Lepidoptera and Hemiptera: Cicadellidae, see Table 1.

Table 1.   Summary of treatment effects for mean insects per trap per day data in sweetcorn experiment evaluating attract treatments (HIPV) and reward (buckwheat)
Treatment effect d.f.Attract 4, 150Reward 1, 150Time 4, 150Attract × Reward 4, 150Time × Attract 16, 150Time × Reward 4, 150Time × Attract × Reward 16, 150Overall meanSquare-root transformed mean
  1. NS, not significant.

  2. *Not analysed because of low trap catches.

 Total of parasitoidsNS<0·001<0·001NSNSNSNS11·833·17
 Total of predatorsNS0·052<0·001NSNSNSNS0·701·07
 Microplitis demolitorNS<0·001<0·001NSNS<0·001NS0·230·83
 Trichogramma pretiosumNS0·002<0·001NSNS0·003NS3·811·73
 Ceranisus sp.NS<0·0010·0010·0030·009<0·001NS1·001·10
 Hemiptera: CicadellidaeNSNSNSNSNS0·014NS0·471·66
 Diptera: Tachinidae*       0·12 
 Ichneumonidae*       0·01 
 Pteromalidae*       0·10 
 Diapriidae*       0·20 
 Lepidoptera (adult)*       0·02 

No synergistic attract and reward effects were apparent for any taxa. The abundance of Eulophidae was significantly higher on traps in all HIPV treatments compared with the control 1 day after spraying (= 2·14, d.f. = 16, 150, P = 0·009; Fig. 1a). Encyrtidae were more numerous near MeJA-treated plants compared to the control but no time effect was apparent (= 6·55, d.f. = 4, 150, P < 0·001; Fig. 1b).


Figure 1.  Mean (√x + 0·5) daily trap catches of parasitoids on non-attracting sticky traps adjacent to sweetcorn plants treated with synthetic herbivore-induced plant volatile compounds (a) Eulophidae for each time period and (b) Encyrtidae all time periods pooled.

Download figure to PowerPoint

The abundance of Braconidae, Trichogrammatidae, Scelionidae, Eulophidae, Mymaridae and Ceraphronidae was significantly greater in treatments with reward (Table 2). Reward was also a significant main effect when all parasitoids were pooled (those named above plus Ichneumonidae, Pteromalidae and Diapriidae) (Table 2). The same trend was apparent for predators (Table 2). A significant time/reward effect was apparent for Microplitis demolitor Wilkinson (Hymenoptera: Braconidae) with greater numbers trapped from day 2 to 18 after spraying (F = 8·03, d.f. = 4, 150, < 0·001; Fig. 2a). Eulophidae were increased by reward for 1 day and from 11 to 22 days after spraying (F = 4·69, d.f. = 4, 150, = 0·001; Fig. 2b). Trichogrammatidae were more abundant 1 day after the spraying (F = 4·09, d.f. = 4, 150, = 0·004; Fig. 2c). Herbivorous thrips were more numerous 1 day after spraying (F = 5·12, d.f. = 4, 150, < 0·001; Fig. 2d).

Table 2.   Mean (√x + 0·5) daily trap catches of taxa on non-attracting sticky traps adjacent to sweetcorn plants for which reward was a significant main effect
TaxaNo rewardRewardSEP-valueFd.f.
Hemiptera: Cicadellidae0·920·870·030·0354·521, 150
Herbivorous thrips2·222·450·110·0344·551, 150
Predators1·031·100·030·0523·831, 150
Parasitoids2·923·400·11<0·00118·571, 150
Trichogrammatidae1·691·950·090·0039·331, 150
Trichogramma pretiosum1·601·870·090·0029·761, 150
Seclionidae1·511·630·060·0543·781, 150
Eulophidae0·971·320·05<0·00143·711, 150
Ceranisus sp.0·931·250·05<0·00137·961, 150
Ceraphronidae1·021·180·04<0·00115·551, 150
Mymaridae0·910·980·040·0384·391, 150
Braconidae0·850·980·03<0·00115·811, 150
Microplitis demolitor0·780·880·02<0·00115·501, 150

Figure 2.  Mean (√x + 0·5) daily trap catches of taxa on non-attracting sticky traps adjacent to sweetcorn, broccoli plants and grapevines for which reward had a temporal effect. (a) Micropiltis demolitor, (b) Eulophidae, (c) Trichogrammatidae and (d) herbivorous thrips in sweetcorn, (e) herbivorous thrips in grapevines, (f) Beneficial parasitoids pooled, (g) Eulophidae, (h) Encyrtidae, (i) herbivorous thrips in broccoli.

Download figure to PowerPoint

In treatments with reward, significantly fewer Helicoverpa spp. larvae were collected from sweetcorn plants in plots with reward (mean = 0·34) than with plots without reward (mean = 1·30) (= 10·05, d.f. = 1, 30, P = 0·003). Helicoverpa spp. damage was also significantly lower in the MeA treatment compared to the control (= 2·86, d.f. = 4, 30, P = 0·04; Fig. 3). Significantly more rodent damage was found on cobs harvested from plots with reward (mean = 2·05%) than plots without reward (mean = 0·12%) (= 9·02, d.f. = 1, 30, P = 0·005).


Figure 3.  Mean (√x + 0·5) Helicoverpa spp. damage found in attract treatments.

Download figure to PowerPoint

Broccoli experiment

In this experiment, 4474 individuals were trapped including 11 hymenopteran families, predators (same taxa as previously described), Diptera: Tachinidae and herbivorous Thysanoptera, adult Lepidoptera and Hemiptera: Cicadellidae, see Table 3.

Table 3.   Summary of treatment effects for mean insects per trap per day data in broccoli experiment evaluating attract treatments (HIPV) and reward (buckwheat)
Treatment effect d.fAttract 4, 150Reward 1, 150Time 4, 150Attract × Reward 4, 150Time × Attract 16, 150Time × Reward 4, 150Time  × Attract × Reward 16, 150Overall meanSquare-root transformed mean
  1. NS, not significant.

  2. *Not analysed because of low trap catches.

 Total of parasitoidsNS<0·001<0·001NSNS0·054NS8·482·78
 Total of predatorsNS<0·0010·004NS0·022NSNS0·661·04
 Diadegma semiclausumNS<0·001<0·001NSNSNSNS2·181·51
 Diptera: TachinidaeNS<0·001NSNSNSNSNS0·230·83
 Lepidoptera (adult)NS0·031<0·001NSNS0·018NS0·400·91
 Hemiptera: CicadellidaeNSNS<0·001NSNSNSNS0·310·87
 Araneidae*       0·18 
 Diapri idae*       0·10 
 Bethylidae*       0·03 

A significant synergistic attract and reward and time effect was apparent for Scelionidae with greater numbers trapped for the first day after spraying near MeSA-treated plants with reward (= 1·80, d.f. = 16, 150, P = 0·036; Fig. 4). Scelionids were also significantly more numerous near HA-treated plants without reward compared to the control 1 day after spraying (= 1·80, d.f. = 16, 150, P = 0·036; Fig. 4). Ceraphronidae responded to MeSA (= 3·09, d.f. = 4, 150, P = 0·018; Fig. 5). Predators were significantly more numerous on traps near HIPV mix-treated plants 1 day after spraying (= 1·92, d.f. = 16, 150, P = 0·022; Fig. 6).


Figure 4.  Mean (√x + 0·5) daily trap catches of Scelionidae on non-attracting sticky traps adjacent to broccoli plants treated with synthetic herbivore-induced plant volatile compounds.

Download figure to PowerPoint


Figure 5.  Mean (√x + 0·5) daily trap catches of Ceraphronidae on non-attracting sticky traps adjacent to broccoli plants treated with synthetic herbivore-induced plant volatile compounds.

Download figure to PowerPoint


Figure 6.  Mean (√x + 0·5) daily trap catches of predatory insects on non-attracting sticky traps adjacent to broccoli plants treated with synthetic herbivore-induced plant volatile compounds.

Download figure to PowerPoint

The abundance of Trichogrammatidae, Eulophidae, Encyrtidae, Pteromalidae, Ichneumonidae and Ceraphronidae was significantly enhanced by the presence of a reward (Table 4). All beneficial parasitoids pooled which included additional families to those above were significantly more abundant in treatments with reward (Table 4). The same trend was identified for predators (Table 4). For all parasitoids a significant time/reward effect was apparent, which were more abundant from day 11 to 24 (= 2·38, d.f. = 4, 150, = 0·054; Fig. 2f). Eulophids were trapped in greater numbers from day 4 to 24 of the sampling period (= 3·15, d.f. = 4, 150, = 0·016; Fig. 2g). Encyrtids were higher in abundance from day 11 to 24 (= 4·68, d.f. = 4, 150, = 0·001; Fig. 2h). Herbivorous thrips were more numerous for 1 day after spraying (= 3·68, d.f. = 4, 150, = 0·007; Fig. 2i). Adult Lepidoptera, including DBM and cabbage white butterfly (CWB) Pieris rapae Linnaeus (Lepidoptera: Pieridae) were trapped less in treatments with reward on day 1 and from day 18 to 24 of the sampling period (= 3·06, d.f. = 4, 150, = 0·018; Fig. 2j). Abundance of DBM larvae (= 1·25, d.f. = 4, 30, = 0·312) and the proportion of parasitized larvae (= 1·01, d.f. = 4, 30, = 0·420) were not significantly different between treatments. The overall parasitism rate of DBM larvae by D. semiclausum was 61%.

Table 4.   Mean (√x + 0·5) daily trap catches of taxa on non-attracting sticky traps adjacent to broccoli plants for which reward was a significant main effect
TaxaNo rewardRewardSEP-valueFd.f.
Lepidoptera (adult)0·950·870·020·0314·751,150
Herbivorous thrips1·551·820·110·0096·921,150
Diptera: Tachinidae0·760·910·07<0·00138·161,150
Diadegma semiclausum1·341·670·02<0·00215·121,150

Vineyard experiment

During the experiments, 1304 individuals were trapped during the first sampling period and 2816 during the second sampling period including 11 hymenopteran families, predators (same taxa as previously described), herbivorous Thysanoptera, adult Lepidoptera and Hemiptera: Cicadellidae, see Table 5.

Table 5.   Summary of treatment effects for mean insects per trap per day data in wine grape experiment evaluating attract treatments (HIPV) and reward (buckwheat)
Treatment effect d.f. (24 February–3 March 2009)Attract 3,72Reward 1,72Time 2,72Attract × Reward 3,72Time × Attract 6,72Time × Reward 2,72Time × Attract × Reward 6,72Overall meanSquare-root transformed mean
  1. NS, not significant.

  2. *Not analysed because of low trap catches.

 Total of parasitoidsNS<0·001<0·001NSNSNSNS6·022·48
 Total of predatorsNSNSNSNSNSNSNS0·401·60
 Lepidoptera (adult)NSNS0·003NSNSNSNS0·911·08
 Hemiptera: Cicadellidae*       0·07 
 Diptera: Tachinidae*       0·01 
 Ichneumonidae*       0·01 
 Diapriidae*       0·09 
 Mymaridae*       0·11 
 Trichogrammatidae*       0·14 
 Pteromalidae*       0·14 
d.f. (10–30 March 2009)3,961,963,963,969,963,969,96  
 Total of parasitoidsNSNS<0·001NSNSNSNS7·642·74
 Total of predatorsNSNS<0·001NSNSNSNS0·781·10
 Lepidoptera (adult)NSNSNSNSNSNSNS0·530·97
 Hemiptera: CicadellidaeNSNS0·024NSNSNSNS0·170·80
 Diptera: Tachinidae*       0·03 
 Diapriidae*       0·08 
 Bethylidae*       0·11 
 Ichneumonidae*       0·04 
 Pteromalidae*       0·04 

In the two sampling periods, no significant impact of the attract treatments for any taxa was apparent (Table 5). Throughout the first sampling period, Eulophidae, Braconidae, Encyrtidae and herbivorous thrips were significantly increased in treatments with reward (Table 6). When these parasitoid families were pooled, along with additional hymenoptera parasitoid taxa that were trapped in numbers too low to allow separate analysis, catches were greater in treatments with reward (Table 6). In this sampling period, herbivorous thrips were more abundant from day 1 to 4 (= 3·43, d.f. = 2, 72, P = 0·038; Fig. 2e). During the second sampling period, Eulophidae, Braconidae and Ceraphronidae were significantly increased in treatments with reward (Table 6) but no time/reward effect was apparent for any taxa (Table 5).

Table 6.   Mean (√x + 0·5) daily trap catches of taxa on non-attracting sticky traps adjacent to grapevines for which reward was a significant main effect
TaxaNo rewardRewardSEP-valueFd.f.
24 February–3 March 2009
 Herbivorous thrips0·791·230·09<0·00123·331,72
10–30 March 2009


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

This study shows that synthetic HIPV spray applications to plant foliage and the incorporation of floral resources within the crop can enhance recruitment and residency of beneficial arthropods in sweetcorn, broccoli and wine-grapes. Our results also indicate that under some conditions this can lead to effects on other trophic levels resulting in fewer pests and reduced insect damage to harvested crop portions. The results support our hypothesis that an ‘attract and reward’ approach based on semiochemical and companion plant effects results in higher abundance of natural enemies compared to HIPV (attract) or floral resources (reward) alone. This is demonstrated in broccoli with an increased abundance of scelionid wasps, egg parasitoids of Helicoverpa spp. near MeSA-treated plants with reward. However, scelionids were also more abundant near plants treated with HA without reward. The ‘attract and reward’ approach differs from the ‘push–pull’ strategy which is also based on semiochemical and companion plant effects. The ‘push–pull’ technique deploys semiochemicals to deter insects away (push) from the main crop and the ‘pull’ component draws pests to a trap crop (Cook, Khan & Pickett 2007).

In this study, eulophid parasitoids were more numerous in all of the HIPV treatments in sweetcorn for 1 day after spraying. The ability of small scelionid and eulophid parasitoids to move towards synthetic compounds in the field has been demonstrated previously (Murai, Imai & Maekawa 2000; Krupke & Brunner 2003; Fatouros et al. 2008). In our sweetcorn experiment, Encyrtidae were attracted to plants treated with MeJA. James & Grasswitz (2005) also demonstrated attraction of an encyrtid wasp Metaphycus sp. to MeJA although MeJA was applied to grapevines in controlled released dispensers (CRD) instead of a spray formulation. In broccoli, Ceraphronidae that parasitize or hyperparasitize various Diptera, parasitic Hymenoptera, Hemiptera and Neuroptera (Naumann 1991) responded to MeSA. Orre et al. (2010) also showed attraction from a fourth-trophic level parasitoid Anacharis zealandica Ashmead (Hymenoptera: Figitidae) to MeSA deployed with CRD in a turnip crop. In broccoli, the HIPV mix increased predators for 1 day after spraying whilst in sweetcorn the HIPV mix resulted in the highest abundance of eulophids compared with other tested HIPVs. Field evidence for attraction of predators to synthetic HIPVs deployed with CRD (James 2005; Yu et al. 2008) and spray application (James in press) has been demonstrated previously.

In this study, water was the control rather than Synertrol® dispersed in water. To maximize spatial treatment separation, the adjuvant treatment was dropped and water retained with the adjuvant remaining a constant across all HIPV treatments. Earlier experiments in the same crops suggested attraction of some taxa to the adjuvant alone. However, significant differences in attraction between the HIPVs, doses and Synertrol® alone suggested that the HIPVs were responsible for attraction of the different taxa (Simpson et al. 2011).

The results from this study suggest that the spray-applied HIPV effects may be short-lived. Simpson et al. (in press) established similar time trends, although abundance of some taxa were increased up to 6 days post-treatment. Most of the HIPVs used in this study are known to induce plants to emit endogenous HIPVs (Yan & Wang 2006; Tamogami, Rakwal & Agrawal 2008). Consequently, an increase in abundance of the observed taxa could also be attributed to emitted endogenous HIPVs. Traps in all of the attract and reward treatments recorded consistently higher numbers of eulophids, encyrtids, ceraphronids and predators than either attract or reward alone; however, abundance was not statistically increased for any one taxon. The inclusion of the reward clearly increased the abundance of several parasitoid families in the crops. Due to the short-lasting HIPV effect, it can be concluded that thereafter the reward is sustaining natural enemies. Key biological control agents increased by the reward included Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) and M. demolitor in sweetcorn, D. semiclausum in broccoli and Dolichogenidae tasmanica Cameron and Bassus sp. (Hymenoptera: Braconidae) in wine-grapes. Previous field studies with buckwheat in vineyards showed increased parasitoid abundance (Berndt, Wratten & Hassan 2002; English-Loeb et al. 2003).

Visual cues from buckwheat flowers may have interfered with volatile cues from applied HIPVs resulting in statistical increases in attract and reward treatments only for scelionids in broccoli. Interference between cues could also explain the lack of response by parasitoids of larger lepidopterous larvae to attract treatments. Treatment plots were spaced 15 m apart in sweetcorn and broccoli and 30 m in the vineyard, which was the maximum spacing possible to accommodate all treatments in each of the field sites. Previous studies established that larval parasitoids can cover far greater distances to forage for hosts and foods. The parasitoid D. semiclausum is capable of moving more than 80–100 m in a short time period (Lavandero et al. 2005; Schellhorn et al. 2008). Wanner et al. (2006) showed that female Cotesia glomerata Linnaeus (Hymenoptera: Braconidae) parasitoids can forage for hosts over distances exceeding 1225 m2 when food sources are nearby. Small egg parasitoids disperse passively by wind or use larger hosts for transportation. However, once in the vicinity of plants, egg parasitoids use volatile cues from the first and second trophic level to establish the presence of the host or its eggs (Fatouros et al. 2008). The distance between treatments used in our study could explain why there were only responses to attract treatments by small egg parasitoids which might have been less likely to be attracted to reward plots at greater distances. Long et al. (1998) identified in mark–recapture studies short distance dispersion of Trichogramma spp. which were not recaptured at 6 or 80 m from the hedgerow in the nearby crop, but in a nearby almond orchard 2·5% of Trichogramma were marked at 6 m from the hedgerow. In our study, Trichogrammatidae or Scelionidae were abundant in sweetcorn but no response to HIPVs was apparent. Perhaps, these parasitoids were more oriented to the kairomones from the Helicoverpa spp. that were present in the crop. These egg parasitoids use host volatiles as foraging cues (Fatouros et al. 2008). Nordlund et al. (1987) and Bruce et al. (2009) demonstrated orientation of Telenomus spp. (Hymenoptera: Scelionidae) and Trichogramma spp. to host volatiles. Clearly, further work at a larger spatial scale with greater treatment separation is necessary before the ecology of this phenomenon and its pest management utility are evident.

For the development of effective CBC strategies, it is crucial to achieve not only increased abundance of natural enemies but also cascading effects on lower trophic levels: reduction in pest numbers and plant damage. The sweetcorn experiment showed reduced abundance of Helicoverpa spp. larvae on sweetcorn plants in treatments with reward. Several field studies successfully demonstrated that the presence of buckwheat enhanced parasitism in broccoli (Lavandero et al. 2005), vineyards (Nagarkatti et al. 2003; Berndt, Wratten & Scarratt 2006) and an apple orchard (Irvin et al. 2006). Our study identified less Helicoverpa spp. damage in sweetcorn cobs harvested from plants treated with MeA compared to the control, an effect that could have been caused by the recruitment of natural enemies. James & Price (2004) showed that a MeSA-baited hop yard increased abundance of predators leading to sub-economic levels of spider-mites. Reduced Helicoverpa spp. damage may also have been the result of induced direct plant defences in sweetcorn plants triggered by the HIPV application, which may have changed the plant’s nutritional quality.

Our results did not establish any benefit to reducing numbers of adult Lepidoptera. However, in broccoli fewer adults were found on traps in treatments with a reward indicating possible feeding of these species on buckwheat flowers. Lee & Heimpel (2005) observed feeding of adult CWB and DBM in buckwheat along cabbage fields but their abundance was not enhanced because eggs numbers were not different to control plots. This could constitute a problem for the use of buckwheat as a reward strategy. Winkler et al. (2009) established that the longevity of CWB and DBM was increased by access to buckwheat nectar and there is some risk this flower could increase pest fecundity in the field. However, longevity of the parasitoid D. semilcausum was more strongly enhanced by buckwheat improving biological control efficacy as its oviposition rate is constant over several weeks (Winkler et al. 2009). Enhanced longevity and fecundity of D. semiclausum by buckwheat were also identified by Lavandero et al. (2006). Thus, the net effect of buckwheat could be reduced pest numbers (via enhanced natural enemy activity) even if the pest’s biology is enhanced.

In our study, herbivorous thrips were increased by the presence of reward. A recent study by Simpson et al. (2011) showed attraction of herbivorous thrips to synthetic HIPVs in sweetcorn and broccoli but in this study abundance of thrips did not differ between attract and control treatments. However, thrips are not regarded as major pests in these cropping systems and therefore their presence can provide alternative prey or hosts for recruited natural enemies. Possibly, a more serious problem of providing nectar plants in the sweetcorn system is indicated by the increased rodent damage. This is likely to reflect the use of buckwheat plants by rodents for shelter. Overall damage was, however, minimal and adverse effects from rodents can be prevented by implementing control options to avoid an increase in numbers. In fact, the presence of buckwheat areas could assist control by concentrating rodents into discrete areas where control measures such as baiting or trapping might be focussed. Overall, the finding that HIPVs and reward plants can attract arthropod herbivores and rodents as well as beneficial insects illustrates the need for caution. Future work needs to identify treatment types and use patterns that minimize negative effects whilst still favouring natural enemies.

The ability and efficiency of natural enemies to move into crops soon after pest incursion is important for reducing the time-lag between pest build up and control by natural enemies (Kean et al. 2003). This time-lag could be reduced by deploying HIPVs in the crop. Reward in the form of floral resources could minimize the redistribution of natural enemies while hosts or prey are low in abundance. Our study is one of the first to combine volatile cues with visual cues as a strategy to enhance CBC of crop pests. Salient findings, such as increased abundance and residency of natural enemies, decrease in pest numbers and crop damage should encourage further studies to develop ‘attract and reward’ as an important strategy for improving CBC.


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The authors thank Jeff West, Donna Read, Karen Gogala and Greg Simpson for help with field work, the growers Clayton Kiely, Jeff McSpedden and Bruce Armstrong for allowing us to conduct the field experiments and Linton Staples for providing methyl anthranilate. Donna Read is thanked for helpful comments on the manuscript. This study was funded by the Australian Research Council.


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  • Baggen, L.R. & Gurr, G.M. (1998) The influence of food on Copidosoma koehleri (Hymenoptera:Encyrtidae), and the use of flowering plants as a habitat management tool to enhance biological control of potato moth, Phthorimaea operculella (Lepidoptera : Gelechiidae). Biological Control, 11, 917.
  • Baggen, L.R., Gurr, G.M. & Meats, A. (1999) Flowers in tri-trophic systems: mechanisms allowing selective exploitation by insect natural enemies for conservation biological control. Entomologia Experimentalis et Applicata, 91, 155161.
  • Begum, M., Gurr, G.M., Wratten, S.D., Hedberg, P.R. & Nicol, H.I. (2006) Using selective food plants to maximize biological control of vineyard pests. Journal of Applied Ecology, 43, 547554.
  • Berndt, L.A., Wratten, S.D. & Hassan, P.G. (2002) Effects of buckwheat flowers on leafroller (Lepidoptera: Tortricidae) parasitoids in a New Zealand vineyard. Agricultural and Forest Entomology, 4, 3945.
  • Berndt, L.A., Wratten, S.D. & Scarratt, S.L. (2006) The influence of floral resource subsidies on parasitism rates of leafrollers (Lepidoptera: Tortricidae) in New Zealand vineyards. Biological Control, 37, 5055.
  • Bone, N.J., Thomson, L.J., Ridland, P.M., Cole, P. & Hoffmann, A.A. (2009) Cover crops in Victorian apple orchards: effects on production, natural enemies and pests across a season. Crop Protection, 28, 675683.
  • Bostanian, N.J., Goulet, H., O’Hara, J., Masner, L. & Racette, G. (2004) Towards insecticide free apple orchards: flowering plants to attract beneficial arthropods. Biocontrol Science & Technology, 14, 2537.
  • Bowie, M.H., Wratten, S.D. & White, A.J. (1995) Agronomy and phenology of ‘‘companion plants’’ of potential for enhancement of insect biological control. New Zealand Journal of Crop and Horticultural Science, 23, 423427.
  • Bruce, A.Y., Schulthess, F., Mueke, J. & Calatayud, P.A. (2009) Olfactory attraction of egg parasitoids to virgin females of noctuid stemborers. BioControl, 54, 763772.
  • Cook, S.M., Khan, Z.R. & Pickett, J.A. (2007) The use of push-pull strategies in integrated pest management. Annual Review of Entomology, 52, 375400.
  • Dicke, M. (1999) Evolution of induced indirect defense of plants. The Ecology and Evolution of Inducible Defenses (eds R.Tollrian & C.D.Harvell), pp. 6288. Princeton University press, Princeton, NJ.
  • Dicke, M., Vanbeek, T.A., Posthumus, M.A., Bendom, N., Vanbokhoven, H. & Degroot, A.E. (1990) Isolation and identification of volatile kairomone that affects acarine predator-prey interactions- involvement of host plant in its production. Journal of Chemical Ecology, 16, 381396.
  • English-Loeb, G., Rhainds, M., Martinson, T. & Ugine, T. (2003) Influence of flowering cover crops on Anagrus parasitoids (Hymenoptera:Mymaridae) and Erythroneura leafhoppers (Homoptera:Cicadellidae) in New York vineyards. Agricultural and Forest Entomology, 5, 173181.
  • Fatouros, N.E., Dicke, M., Mumm, R., Meiners, T. & Hilker, M. (2008) Foraging behavior of egg parasitoids exploiting chemical information. Behavioral Ecology, 19, 677689.
  • Gurr, G.M., Wratten, S.D. & Altieri, M.A. (2004) Ecological Engineering: Advances in Habitat Manipulation for Arthropods. CSIRO Publishing, Melbourne, Vic., Australia.
  • Irvin, N.A., Scarratt, S.L., Wratten, S.D., Frampton, C.M., Chapman, R.B. & Tylianakis, J.M. (2006) The effects of floral understoreys on parasitism of leafrollers (Lepidoptera:Tortricidae) on apples in New Zealand. Agricultural and Forest Entomology, 8, 2534.
  • James, D.G. (2005) Further field evaluation of synthetic herbivore-induced plant volatiles as attractants for beneficial insects. Journal of Chemical Ecology, 31, 481495.
  • James, D.G. (in press) Grape and hop plants sprayed with botanical oil pesticides containing herbivore-induced plant volatiles attract insect predators and parasitoids. Environmental Entomology.
  • James, D.G. & Grasswitz, T.R. (2005) Synthetic herbivore-induced plant volatiles increase field captures of parasitic wasps. BioControl, 50, 871880.
  • James, D.G. & Price, T.S. (2004) Field-testing of methyl salicylate for recruitment and retention of beneficial insects in grapes and hops. Journal of Chemical Ecology, 30, 16.
  • Jervis, M.A., Kidd, N.A.C., Fitton, M.G., Huddleston, T. & Dawah, H.A. (1993) Flower-visiting by hymenopteran parasitoids. Journal of Natural History, 27, 67105.
  • Karban, R. & Baldwin, I.T. (1997) Induced Responses to Herbivory. The University of Chicago, Chicago, IL.
  • Kean, J., Wratten, S., Tylianakis, J. & Barlow, N. (2003) The population consequences of natural enemy enhancement, and implications for conservation biological control. Ecology Letters, 6, 604612.
  • Khan, Z.R., James, D.G., Midega, C.A.O. & Pickett, J.A. (2008) Chemical ecology and conservation biological control. Biological Control, 45, 210224.
  • Krupke, C.H. & Brunner, J.F. (2003) Parasitoids of the consperse stink bug (Hemiptera:Pentatomidae) in north central Washington and attractiveness of a host-produced pheromone component. Journal of Entomological Science, 38, 8492.
  • Landis, D.A., Wratten, S.D. & Gurr, G.M. (2000) Habitat Management to conserve natural enemies of arthropod pests in agriculture. Annual Review of Entomology, 45, 175.
  • Lavandero, B., Wratten, S., Shishehbor, P. & Worner, S. (2005) Enhancing the effectiveness of the parasitoid Diadegma semiclausum (Helen): movement after use of nectar in the field. Biological Control, 34, 152158.
  • Lavandero, B., Wratten, S.D., Didham, R.K. & Gurr, G. (2006) Increasing floral diversity for selective enhancement of biological control agents: a double-edged sward? Basic and Applied Ecology, 7, 236243.
  • Lee, J.C. & Heimpel, G.E. (2005) Impact of flowering buckwheat on Lepidopteran cabbage pests and their parasitoids at two spatial scales. Biological Control, 34, 290301.
  • Lewis, W.J., Stapel, J.O., Cortesero, A.M. & Takasu, K. (1998) Understanding how parasitoids balance food and host needs: importance to biological control. Biological Control, 11, 175183.
  • Long, R.F., Corbett, A., Lamb, C., Reberg-Horton, C., Chandler, J. & Stimmann, M. (1998) Beneficial insects move from flowering plants to nearby crops. California Agriculture, 52, 2326.
  • Murai, T., Imai, T. & Maekawa, M. (2000) Methyl anthranilate as an attractant for two thrips species and the thrip parasitoid Ceranisus menes. Journal of Chemical Ecology, 26, 25572565.
  • Nagarkatti, S., Tobin, P.C., Saunders, M.C. & Muza, A.J. (2003) Release of native Trichogramma minutum to control grape berry moth. Canadian Entomologist, 135, 589598.
  • Naumann, I.D. (1991) The Insects of Australia: A Textbook for Students and Research Workers, 2nd edn. Melbourne University Press, Melbourne, Vic., Australia.
  • Nordlund, D.A., Strand, M.R., Lewis, W.J. & Vinson, S.B. (1987) Role of kairomones from host accessory-gland secretion in host recognition by Telenomus remus and Trichogramma pretiosum, with partial characterization. Entomologia Experimentalis et Applicata, 44, 3743.
  • Orre, G.U.S., Wratten, S.D., Jonsson, M. & Hale, R.J. (2010) Effects of an herbivore-induced plant volatile on arthropods from three trophic levels in brassicas. Biological Control, 53, 6267.
  • Paré, P.W. & Tumlinson, J.H. (1999) Plant volatiles as a defense against insect herbivores. Plant Physiology, 121, 325331.
  • Payne, R.W., Murray, D.A., Harding, S.A., Baird, D.B. & Soutar, D.M. (2009) Genstat for Windows (12th Edition) Introduction. VSN International, Hemel Hempstead.
  • Schellhorn, N.A., Bellati, J., Paull, C.A. & Maratos, L. (2008) Parasitoid and moth movement from refuge to crop. Basic and Applied Ecology, 9, 691700.
  • Simpson, M., Gurr, G.M., Simmons, A.T., Wratten, S.D., James, D.G., Leeson, G. & Nicol, H.I. (2011) Insect attraction to synthetic herbivore-induced plant volatile-treated field crops. Agricultural and Forest Entomology, 13, 4557.
  • Stevens, N.B., Stephens, C.J., Iqbal, M., Jennings, J.T., La Salle, J. & Austin, A.D. (2007) What Wasp is That? An Interactive Identification Guide to the Australasian Families of Hymenoptera. Australian Biological Resources Study (ABRS) and Centre for Biological Information Technology (CBIT), Canberra.
  • Tamogami, S., Rakwal, R. & Agrawal, G.K. (2008) Interplant communication: airborne methyl jasmonate is essentially converted into JA and JA-Ile activating jasmonate signaling pathway and VOCs emission. Biochemical and Biophysical Research Communications, 376, 723727.
  • Thaler, J.S. (1999) Jasmonate-inducible plant defences cause increased parasitism of herbivores. Nature, 399, 686.
  • Van Den Boom, C.E.M., Van Beek, T.A., Posthumus, M.A., De Groot, A. & Dicke, M. (2004) Qualitative and quantitative variation among volatile profiles induced by Tetranychus urticae feeding on plants from various families. Journal of Chemical Ecology, 30, 6989.
  • Wäckers, F.L. & Lewis, W.J. (1994) Olfactory and visual learning and their combined influence on host site location by the parasitoid Microplitis croceipes (Cresson). Biological Control, 4, 105112.
  • Wanner, H., Gu, H.N., Gunther, D., Hein, S. & Dorn, S. (2006) Tracing spatial distribution of parasitism in fields with flowering plant strips using stable isotope marking. Biological Control, 39, 240247.
  • Whalon, M.E., Mota-Sanchez, D. & Hollingworth, R.M. (2008) Global Pesticide Resistance in Arthropods. CAB Internaional, Cambridge.
  • Winkler, K., Wäckers, F.L., Kaufman, L.V., Larraz, V. & van Lenteren, J.C. (2009) Nectar exploitation by herbivores and their parasitoids is a function of flower species and relative humidity. Biological Control, 50, 299306.
  • Witting-Bissinger, B.E., Orr, D.B. & Linker, H.M. (2008) Effects of floral resources on fitness of the parasitoids Trichogramma exiguum (Hymenoptera:Trichogrammatidae) and Cotesia congregata (Hymenoptera:Braconidae). Biological Control, 47, 180186.
  • Yan, Z.G. & Wang, C.Z. (2006) Wound-induced green leaf volatiles cause the release of acetylated derivatives and a terpenoid in maize. Phytochemistry, 67, 3442.
  • Yu, H.L., Zhang, Y.J., Wu, K.M., Gao, X.W. & Guo, Y.Y. (2008) Field-testing of synthetic herbivore-induced plant volatiles as attractants for beneficial insects. Environmental Entomology, 37, 14101415.
  • Zhu, J. & Park, K.C. (2005) Methyl salicylate, a soybean aphid-induced plant volatile attractive to the predator Coccinella septempunctata. Journal of Chemical Ecology, 31, 17331746.