Synthetic Herbivore-induced Plant Volatiles Research Articles

Exposure to sugarcane borer‐induced plant volatile (E)‐caryophyllene enhances parasitoid recruitment

AbstractPredators and parasitoids locate herbivore‐infested plants via detection of herbivore‐induced plant volatiles (HIPVs) that are released in response to pest damage. Synthetic HIPVs have been proposed as tools to enhance the biological control of crop pests. The sugarcane borer, Diatraea saccharalis (Fabricius) (Lepidoptera: Pyralidae), is a key herbivore pest of sugarcane, Saccharum spp. (Poaceae), in the Americas. To manage D. saccharalis in Brazil, more than 3 million ha of sugarcane have been treated with the larval parasitoid Cotesia flavipes (Cameron) (Hymenoptera: Braconidae). In this study, the role of sugarcane HIPVs as cues in the host‐finding process of C. flavipes was investigated using a combination of dynamic headspace collection, chemical analysis, and laboratory behavior experiments. Comparison of volatile organic compounds (VOCs) collected from D. saccharalis‐damaged and healthy sugarcane revealed very similar profiles, apart from significantly higher levels of the sesquiterpene (E)‐caryophyllene released from damaged plants. Naive female C. flavipes spent significantly more time in the olfactometer arm containing VOCs from D. saccharalis‐damaged plants but showed no preference for VOCs from healthy plants. When (E)‐caryophyllene was added to VOCs from healthy plants, parasitoids spent more time in the arm containing the combined treatment. Furthermore, in a dose–response experiment with synthetic (E)‐caryophyllene, naive parasitoids preferred the compound across a dose range of 3–300 ng, and experienced parasitoids – preexposed to (E)‐caryophyllene – responded to doses of (E)‐caryophyllene as low as 0.03 ng. These results suggest that C. flavipes can use (E)‐caryophyllene as a cue to locate D. saccharalis‐infested sugarcane plants. Moreover, experienced females appear to respond to lower doses than naive females. These results potentially pave the way for increasing the efficiency of C. flavipes in biological control of D. saccharalis, the most important pest of sugarcane and maize crops in the Western Hemisphere, and also a major pest of rice and sorghum crops.

Interactive Effects of an Herbivore-Induced Plant Volatile and Color on an Insect Community in Cranberry.

Synthetic herbivore-induced plant volatiles (HIPVs) could be used to monitor insect populations in agroecosystems, including beneficial insects such as natural enemies of herbivores. However, it is unknown whether insect responses to HIPVs are influenced by visual cues, e.g., color. We hypothesized that the HIPV methyl salicylate (MeSA) interacts with color to affect insect captures on sticky traps. To test this, we conducted a 5 × 2 factorial field experiment in a commercial cranberry farm to monitor numbers of insect predators, parasitoids, and herbivores by using five colored sticky traps that were either baited with a MeSA lure (named 'PredaLure') or unbaited. At the community level, PredaLure increased captures of predators. At the individual-taxon level, captures of the hoverfly Toxomerus marginatus (Diptera: Syrphidae) and thrips (Thysanoptera: Thripidae) were higher on PredaLure-baited traps. However, only captures of T. marginatus on PredaLure-baited traps interacted significantly with color such that the numbers of this hoverfly on yellow and white traps were 2-4 times higher when baited with PredaLure. This study is the first to document the interactive effects of synthetic HIPVs and color on an insect community. Our findings have implications for optimal selection of HIPV-baited colored traps to monitor natural enemy populations in agroecosystems.

Recruiting on the Spot: A Biodegradable Formulation for Lacewings to Trigger Biological Control of Aphids.

Upon herbivory, plants release herbivore-induced plant volatiles (HIPVs), which induce chemical defenses in the plant as well as recruit natural enemies. However, whether synthetic HIPVs can be employed to enhance biological control in a cultivated crop in the field is yet to be explored. Here we show that a biodegradable formulation loaded with induced and food-signaling volatiles can selectively recruit the common green lacewing, Chrysoperla carnea, and reduce pest population under field conditions. In apple orchards, the new formulation attracted lacewing adults over a 4-week period, which correlated well with independent assessments of the longevity of the slow-release matrix measured through chemical analyses. In barley, lacewing eggs and larvae were significantly more abundant in treated plots, whereas a significant reduction of two aphid species was measured (98.9% and 93.6% of population reduction, for Sitobion avenae and Rhopalosiphum padi, respectively). Results show the potential for semiochemical-based targeted recruitment of lacewings to enhance biological control of aphids in a field setting. Further research should enhance selective recruitment by rewarding attracted natural enemies and by optimizing the application technique.

Cascading effects of combining synthetic herbivore-induced plant volatiles with companion plants to manipulate natural enemies in an agro-ecosystem.

Whether tactics to manipulate natural enemies in agro-ecosystems enhance their ecosystem function and services remains debatable. We conducted field experiments in 2015-2016 to test the hypothesis that attraction of natural enemies to herbivore-induced plant volatiles (HIPVs), alone or in combination with companion plants, increases crop productivity. Our treatments consisted of bean plants alone or baited with methyl salicylate (MeSA; an HIPV), or combined with coriander (a companion plant), or with both MeSA and coriander. Numbers of arthropods were visually sampled in each treatment. Sentinel aphids were used to measure ecosystem function (i.e. predation). Plant damage and biomass, and the number and weight of pods and seeds, were measured as a proxy for ecosystem services. MeSA and coriander, when alone or combined, increased the abundance of insect predators from six families, reduced herbivore (e.g. spider mite and thrips) populations, and increased aphid predation. MeSA and coriander also reduced damage by spider mites. MeSA with or without coriander did not, however, increase crop biomass or any yield parameters. MeSA alone or combined with coriander attracted different predator communities, altered pest communities, and reduced damage; however, these results did not cascade down to improve crop productivity. © 2018 Society of Chemical Industry.

Field Trapping of Predaceous Insects With Synthetic Herbivore-Induced Plant Volatiles in Cotton Fields

Nine herbivore-induced plant volatiles (HIPVs) and one methyl jasmonate were field-tested for their attractiveness to the main predators in cotton fields of North China in 2 yr. The main predators including ladybird beetles (Propylaea japonica (Thunberg), Harmonia axyridis (Pallas)), green lacewings (Chrysoplera sinica (Tjeder), Chrysopa spp.), predatory bugs (Geocoris pallidipennis (Costa), Orius spp., Nabis spp.) and spiders (Misumenops tricuspidatus (Fabricius), Erigonidium graminicolum (Sundevall)) were investigated. Two-way ANOVA indicated that the volatile compound, year, and the volatile compound × year interaction affected the behavioral responses of predators. It was found that indole significantly attracted the ladybird beetle P. japonica, H. axyridis. Linalool could attract P. japonica. Green lacewing C. sinica was significantly attracted by α-pinene and β-pinene, whereas indole significantly attracted Chrysopa spp. Methyl jasmonate and α-pinene showed significant attraction to small-flower bug Orius spp. In addition, the attraction of α-humulene to C. sinica, attractiveness of β-pinene to Orius spp. and Chrysopa spp., were observed only in one of the two years. However, the big-eyed bug G. pallidipennis, damsel bug Nabis spp., spiders M. tricuspiata and E. graminicolum did not respond to any of the tested HIPVs. These results are discussed with respect to possible applications of a synthetic attractant for main predators in cotton fields.

Attraction responses of ladybird beetle Hippodamia variegata (Goeze, 1777) (Coleoptera: Coccinellidae) to single and binary mixture of synthetic herbivore-induced plant volatiles in laboratory tests

Yaprakbiti avcisi coccinellid turu Hippodamia variegata (Goeze, 1777) (Coleoptera: Coccinellidae)’nin zararlilar tarafindan tesvik edilen (HIPV) kokularinin dort farkli sentetik formunun [methyl salicylate (MeSA), (E)-2-hexenal (E(2)H), farnesene (F) ve benzaldehyde (Be)] tek basina ve ikili kombinasyonlarinin [MeSA+F, MeSA+E(2)H, MeSA+Be, E(2)H+F ve Be+F] iki farkli dozuna (0.001 ve 1 g/L) olan kimyasal algilama cevaplari test edilmistir. Bocegin cevaplari laboratuvar kosullarinda iki secenekli Y-tup olfaktometre ile degerlendirilmistir. Kontrol olarak kullanilan saf hekzana gore, MeSA’nin dusuk dozu onemli bir sekilde daha fazla H. variegata erginini (%71) cezbetmistir. Ayrica, H. variegata erginleri Be, E(2)H ve F’nin tekli kombinasyonlari ile onemli duzeyde cezbedilememistir. Diger taraftan, MeSA’nin Be ve F ile ikili kombinasyonlarinin kontrole gore onemli bir sekilde daha fazla H. variegata disisini cektigi belirlenmistir. Sonuc olarak, bu bilesikler (Be ve F) MeSA ile birlikte kullanildiginda erginlerin cezbedilmesini arttirmislardir. Gelecekte, bu bulgularin desteklenmesi icin bu avci bocegin arazi kosullarinda cezbedildigi kokulara yoneliminin izlenecegi ek calismalarin yapilmasi gerekmektedir.

Evaluation of airborne methyl salicylate for improved conservation biological control of two-spotted spider mite and hop aphid in Oregon hop yards

The use of synthetic herbivore-induced plant volatiles (HIPV) to attract natural enemies has received interest as a tool to enhance conservation biological control (CBC). Methyl salicylate (MeSA) is a HIPV that is attractive to several key predators of two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and hop aphid, Phorodon humuli (Schrank) (Homoptera: Aphididae). A 2-year study was conducted to evaluate the recommended commercial use of MeSA in hop yards in Oregon. Slow-release MeSA dispensers were stapled to supporting poles in 0.5ha plots and these plots were compared to a paired non-treated plot on each of three farms in 2008 and 2009. Across both years, there was a trend for reduced (range 40-91%) mean seasonal numbers of T. urticae in five of the six MeSA-baited plots. Stethorus spp., key spider mite predators, tended to be more numerous in MeSA-baited plots compared to control plots on a given farm. Mean seasonal densities of hop aphid and other natural enemies (e.g., Orius spp. and Anystis spp.) were similar between MeSA-treated and control plots. Variability among farms in suppression of two-spotted spider mites and attraction of Stethorus spp. suggests that the use of MeSA to enhance CBC of spider mites in commercial hop yards may be influenced by site-specific factors related to the agroecology of individual farms or seasonal effects that require further investigation. The current study also suggests that CBC of hop aphid with MeSA in this environment may be unsatisfactory.

Attract and reward: combining chemical ecology and habitat manipulation to enhance biological control in field crops

Summary 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.

Effects of an herbivore-induced plant volatile on arthropods from three trophic levels in brassicas

Synthetic herbivore-induced plant volatiles (HIPVs) attract arthropod natural enemies showing potential for enhancing biological control. However, HIPVs can also affect the behavior of arthropod herbivores and possibly higher-order natural enemies, potentially complicating the use of HIPVs in biological control. The aim of our work is to understand the effects of one HIPV on the abundance of arthropods at three trophic levels. Of particular interest are effects on herbivores and enemies of natural enemies. A field experiment was carried out in turnip Brassica rapa L. (Brassicaceae) (cv. Green Globe). A randomized block design was used with a treatment of synthetic methyl salicylate (MeSA), and a control consisting of the crop alone. Yellow sticky traps were used for sampling aerial brassica pests, their natural enemies and fourth trophic-level natural enemies within the crop. Our results showed that the abundance of the diamondback moth parasitoid, Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae), the brassica leafmining pest Scaptomyza flava Fallén (Diptera: Drosophilidae), and the lacewing parasitoid, Anacharis zealandica Ashmead (Hymenoptera: Figitidae), increased significantly in the MeSA-treatment compared with the controls. Significantly more D. semiclausum females were attracted to MeSA than were males. However, it still remains unclear whether it is MeSA and/or volatiles produced by induced host plants that are attractive to the arthropods. These results are highly relevant to potential future application of HIPVs in pest management, as the attraction of arthropods within ‘untargeted’ trophic-levels may disrupt trophic cascades and challenges the ideas that the deployment of synthetic HIPVs in pest management may enhance biological control.

Field-Testing of Synthetic Herbivore-Induced Plant Volatiles as Attractants for Beneficial Insects

Seven synthetic herbivore-induced plant volatiles (HIPVs) and a mixture of nonanal + (Z)-3-hexen-1-ol were field tested for their ability to attract beneficial insects in an open cotton field. Eleven species of the main natural enemies of insect pests in cotton fields were studied. Significantly greater numbers of the ladybird beetle Coccinella septempunctata were trapped on (Z)-3-hexenyl acetate-baited cards than on others that were HIPV baited or the control cards. Erigonidium graminicolum was attracted to traps baited with nonanal, (Z)-3-hexenyl acetate, and methyl salicylate (MeSA). The predatory bug Deraeocoris punctulatus was only attracted to traps baited with octanal. The predatory bug Orius similis responded to traps baited with 3,7-dimethyl,1,3,6-octatriene, nonanal, (Z)-3-hexenyl acetate, nonanal + (Z)-3-hexen-1-ol, and MeSA. Dimethyl octatriene, nonanal + (Z)-3-hexen-1-ol, and octanal significantly attracted the syrphid fly Paragus quadrifasciatus. The ladybird beetle Propylaea japonica, the green lacewing Chrysopa sinica, the bigeyed bug Geocoris pallidipennis, the syrphid fly Epistrophe balteata, and the parasitic wasp Campoletis chlorideae did not respond to any of the HIPVs tested. These results are discussed with regard to the potential of HIPVs as tools for recruiting natural enemies into cotton fields.

Chemical ecology and conservation biological control

Elucidating the chemical ecology of natural enemies, herbivores and host plants is important in the development of effective and successful integrated pest management (IPM) strategies where abundance and distribution of natural enemies could be manipulated by semiochemicals for improved conservation biological control (CBC). In response to attack by herbivores, plants produce semiochemicals called Herbivore-Induced Plant Volatiles (HIPVs) which act to repel pests and attract their natural enemies. Damaged, and in some cases, intact plants may also produce volatile signals that warn other plants of impending attack. Some of these intact plants are used as intercrops in ‘push–pull’ strategies; cropping systems based on stimulo-deterrent principle, where the target crop is intercropped with herbivore repellent plants (push) while attractant plants (pull) are planted around this intercrop. The intercrop, in addition to repelling the herbivores, attracts and conserves natural enemies thereby ensuring continued suppression of the pests. This natural delivery of semiochemicals for CBC is currently being exploited by smallholder farmers in eastern Africa in the management of cereal stemborers in maize and sorghum. Synthetic HIPVs also have the potential to effectively recruit natural enemies, thereby improving CBC as has been demonstrated in a series of field experiments in vineyards and hop yards in the Pacific Northwest of the United States. Potentially, plants could be ‘turned on’ by synthetic HIPV signals, and therefore become sources of natural enemy-recruiting volatiles. With the rapid development of plant molecular biology, modification of secondary plant metabolism is also possible which could allow appropriate semiochemicals to be generated by plants at certain growth stages. By identifying the promoter sequences associated with external plant signals that induce biochemical pathways, plant defense genes could be ‘switched on’ prior to insect attack. We review recent research on ‘push–pull’ strategies and synthetic HIPVs in recruitment of beneficial arthropods and warding off pest attack.

Synthetic Herbivore-induced Plant Volatiles Increase Field Captures of Parasitic Wasps

Field evidence for attraction of parasitic wasps from the families Encyrtidae and Mymaridae to grapevines baited with synthetic versions of three herbivore-induced plant volatiles (HIPV) is presented. In a replicated experiment conducted in a juice grape vineyard, sticky cards in blocks baited with controlled-release dispensers of methyl salicylate (MeSA), methyl jasmonate (MeJA) or (Z)-3-hexenyl acetate (HA), trapped significantly greater numbers of Metaphycus sp. (Encyrtidae) than cards in unbaited blocks during May–September. Significantly greater numbers of Anagrus spp. (Mymaridae) were trapped in MeSA and MeJA-baited blocks than in unbaited blocks, during August–September. Greater numbers were recorded in HA-baited blocks in September only. Previous studies showed Encyrtidae and Anagrus spp. were not attracted to sticky cards baited with vials of MeSA, MeJA or HA. Possible reasons for attraction in this study are discussed including the possibility that synthetic, gaseous HIPV from controlled-release dispensers may stimulate plants to produce natural blends of parasitoid-attracting volatiles.

Further Field Evaluation Of Synthetic Herbivore-Induced Plan Volatiles As Attractants For Beneficial Insects

Fifteen synthetic herbivore-induced plant volatiles (HIPVs) were field-tested for attractivity to beneficial insects in two experiments conducted in an open field and a hop yard in Washington State. Eleven insect species or families showed significant attraction to 13 HIPVs. The ladybeetle, Stethorus punctum picipes, was attracted to sticky traps baited with methyl salicylate (MeSA), cis-3-hexen-1-ol (He), and benzaldehyde (Be). The minute pirate bug, Orius tristicolor, was attracted to traps baited with MeSA, He, Be, and octyl aldehyde (Oa), and the bigeyed bug, Geocoris pallens, responded to MeSA, indole, and trans-2-hexen-1-al. The mymarid wasp, Anagrus daanei, was attracted to He, Oa, and farnesene. The chloropid fly, Thaumatomyia glabra, was highly attracted to methyl anthranilate. Insect families responding to HIPVs included Syrphidae (MeSA, He), Braconidae ((Z)-3-hexenyl acetate, He, cis-jasmone (J), methyl jasmonate (MeJA), methyl anthranilate (MeA)), Empididae (MeSA), Sarcophagidae (MeSA, Be, J, nonanal and geraniol), Tachinidae (Be), and Agromyzidae (MeSA). Micro-Hymenoptera (primarily parasitic wasp families) were attracted to MeSA, He, and indole. These results are discussed with respect to known properties and bioactivity of the tested HIPVs and to their potential as tools for recruiting natural enemies into agroecosystems.

Synthetic Herbivore-Induced Plant Volatiles as Field Attractants for Beneficial Insects

Abstract Evidence for field attraction by beneficial insects to synthetic herbivore-induced plant volatiles (HIPVs) is presented. Three synthetic HIPVs (methyl salicylate, (Z)-3-hexenyl acetate, (E)-4,8-dimethyl-1,3,7-nonatriene) were evaluated in a Washington state hop yard during April–October 2002 for attractiveness to beneficial insects. The predatory mirid, Deraeocoris brevis (Uhler), and the anthocorid, Orius tristicolor (White), were attracted to sticky cards baited with (E)-3-hexenyl acetate, while the geocorid, Geocoris pallens Stal., and hover flies (Syrphidae) were attracted to methyl salicylate-baited cards. The coccinellid, Stethorus punctum picipes (Casey), was attracted to both HIPVs in July and September. The (E)-4,8-dimethyl-1,3,7-nonatriene did not attract any beneficial insects. Lygus hesperus Knight, Leptothrips mali (Fitch), Anagrus spp., other Miridae, Coccinellidae, and parasitic Hymenoptera were not attracted to the three HIPVs tested. The possible exploitation of HIPVs in enhancin...