Development of 2‐phenylethanol plus acetic acid lures to monitor obliquebanded leafroller (Lepidoptera: Tortricidae) under mating disruption

We evaluated the effectiveness of 2‐phenylethanol (PET) in combination with acetic acid (AA) as a binary lure for monitoring male and female obliquebanded leafroller, Choristoneura rosaceana (Harris). Studies were conducted in apple, Malus domestica Borkhausen, orchards treated with or without sex pheromone dispensers for mating disruption (MD). Open polypropylene vials, closed membrane cups, and rubber septa loaded with AA and/or PET in varying amounts were first evaluated in a series of trapping experiments. Membrane cups loaded with 800 mg of PET were as effective as 10‐mg septa, but longer lasting, and were comparable to the open vials. A membrane cup AA lure was effective in tests, but further work is needed to increase its release rate and extend its activity. Catches of codling moth, Cydia pomonella (L.), and C. rosaceana were unaffected by combining PET with (E,E)‐8,10‐dodecadien‐1‐ol, the sex pheromone of codling moth, pear ester, (E,Z)‐2,4‐ethyl‐decadienoate and AA lures. Adding (E)‐4,8‐dimethyl‐1,3,7‐nonatriene to this blend to enhance codling moth catch significantly reduced catches of C. rosaceana. PET + AA was a more attractive binary lure than AA plus phenylacetonitrile (PAN) for C. rosaceana. The addition of PET or PAN to traps already baited with the sex pheromone of C. rosaceana significantly reduced male catches. Traps baited with PET + AA placed in blocks not treated with MD caught significantly fewer C. rosaceana than traps baited with sex pheromone. In comparison, sex pheromone‐baited traps in MD blocks caught ≤1 male moth per season which was significantly lower than total moth (>10) or female moth (≥3) catch in these blocks with PET + AA. A high proportion (>70%) of trapped females were mated in both untreated and MD‐treated orchards. Further refinement of this binary, bisexual lure using membrane cup technology may allow the establishment of action thresholds and improve management timings for C. rosaceana.     

Response of mirid predators to synthetic herbivore‐induced plant volatiles

Zoophytophagous plant bugs feed on plant tissue as a source of water and nutrients, besides feeding on prey. By phytophagy, mirid predators activate plant defense responses through different pathways, resulting, among others, in the release of herbivore‐induced plant volatiles (HIPVs). These compounds could repel herbivores and attract parasitoids and predators, and synthetic versions could potentially be used in biological control. Nevertheless, little is known about the influence of synthetic volatiles on mirid attraction. Using Y‐tube olfactometer trials, we evaluated the responses of Nesidiocoris tenuis (Reuter), Macrolophus pygmaeus (Rambur), and Dicyphus bolivari Lindberg (Hemiptera: Miridae), important natural enemies used to control various greenhouse pests, to 10 synthetic versions of HIPVs released from tomato (Solanum lycopersicum L., Solanaceae) plants induced by N. tenuis and M. pygmaeus. Nesidiocoris tenuis responded to five of the 10 HIPVs, whereas M. pygmaeus and D. bolivari responded to four of the 10 HIPVs. Two green leaf volatiles, (Z)‐3‐hexenyl propanoate and (Z)‐3‐hexenyl acetate, and the ester methyl salicylate (MeSA) were attractive to all three mirid predator species. Our results demonstrate that the volatiles released by tomato plants activated by N. tenuis and M. pygmaeus phytophagy are attractive to their conspecifics and also to D. bolivari. Further studies should evaluate the potential of these compounds to attract predatory mirids in the field.     

An ecogenomic analysis of herbivore‐induced plant volatiles in Brassica juncea

Upon herbivore feeding, plants emit complex bouquets of induced volatiles that may repel insect herbivores as well as attract parasitoids or predators. Due to differences in the temporal dynamics of individual components, the composition of the herbivore‐induced plant volatile (HIPV) blend changes with time. Consequently, the response of insects associated with plants is not constant either. Using Brassica juncea as the model plant and generalist Spodoptera spp. larvae as the inducing herbivore, we investigated herbivore and parasitoid preference as well as the molecular mechanisms behind the temporal dynamics in HIPV emissions at 24, 48 and 72 h after damage. In choice tests, Spodoptera litura moth preferred undamaged plants, whereas its parasitoid Cotesia marginiventris favoured plants induced for 48 h. In contrast, the specialist Plutella xylostella and its parasitoid C. vestalis preferred plants induced for 72 h. These preferences matched the dynamic changes in HIPV blends over time. Gene expression analysis suggested that the induced response after Spodoptera feeding is mainly controlled by the jasmonic acid pathway in both damaged and systemic leaves. Several genes involved in sulphide and green leaf volatile synthesis were clearly up‐regulated. This study thus shows that HIPV blends vary considerably over a short period of time, and these changes are actively regulated at the gene expression level. Moreover, temporal changes in HIPVs elicit differential preferences of herbivores and their natural enemies. We argue that the temporal dynamics of HIPVs may play a key role in shaping the response of insects associated with plants.     

Cannibalism of parasitoid‐attacked conspecifics in a non‐carnivorous caterpillar

Cannibalism, the killing and consumption of conspecifics, can even occur in insect species typically considered to be non‐carnivorous. Of particular interest is the cannibalism of parasitoid‐attacked conspecifics, which could reduce parasitism levels in subsequent generations for that conspecific population. This study reports on the occurrence and some of the consequences of cannibalism in parasitoid‐attacked obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae). We show that larvae of C. rosaceana, which is considered to be an herbivorous caterpillar species, did not prey upon live conspecifics, but readily consumed conspecifics attacked by Habrobracon gelechiae Ashmead (Hymenoptera: Braconidae). Further examination found that C. rosaceana larvae feeding on parasitoid‐attacked conspecifics, since their fourth instar, suffered a higher mortality and reduction in body size than those fed on plant material only. The cannibalism of attacked conspecifics did not appear to offer any nutrient benefits for the cannibal. To our best knowledge, this is the first empirical example of the occurrence and some of the consequences of cannibalism by a non‐carnivorous insect on its parasitoid‐attacked conspecifics. We discuss the adaptive significance of such cannibalism on parasitoid‐attacked conspecifics with respect to a trans‐generational fitness gain for the population through the killing of the parasitoids, thereby reducing parasitism in subsequent generations.     

Root damage to apple plants by cockchafer larvae induces a change in volatile signals below‐ and above‐ground

Volatile organic compounds (VOCs) mediate communication between plants and insects. Plants under insect herbivore attack release VOCs either at the site of attack or systemically, indicating within‐plant communication. Some of these VOCs, which may be induced only upon herbivore attack, recruit parasitoids and predatory insects to feed on the attacking insects. Moreover, some plants are able to ‘eavesdrop’ on herbivore‐induced plant volatiles (HIPVs) to prime themselves against impending attack; such eavesdropping exemplifies plant–plant communication. In apple orchards, the beetle Melolontha melolontha L. (Coleoptera: Scarabaeidae) is an important insect pest whose larvae live and feed on roots for about 4 years. In this study, we investigated whether the feeding activity of M. melolontha larvae (1) alters the volatile profile of apple roots, (2) induces the release of HIPVs systemically in the leaves, and (3) whether infested plants communicate to neighbouring non‐infested conspecifics through HIPVs. To answer these questions, we collected constitutive VOCs from intact M9 roots as well as M. melolontha larvae‐damaged roots using a newly designed ‘rhizobox’, to collect root‐released volatiles in situ, without damaging the plant root system. We also collected VOCs from the leaf‐bearing shoots of M9 whose roots were under attack by M. melolontha larvae and from shoots of neighbouring non‐infested conspecifics. Gas chromatography‐mass spectrometry analysis showed that feeding activity of M. melolontha larvae induces the release of specific HIPVs; for instance, camphor was found in the roots only after larvae caused root damage. Melolontha melolontha also induced the systemic release of methyl salicylate and (E,E)‐α‐farnesene from the leaf‐bearing shoots. Methyl salicylate and (E,E)‐α‐farnesene were also released by the shoots of non‐infested neighbouring conspecifics. These phenomena indicate the induction of specific VOCs below‐ and above‐ground upon M. melolontha larvae feeding on apple roots as well as plant–plant communication in apple plants.     

Effects of quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested maize on the attraction of the larval parasitoid Cotesia kariyai

Cotesia kariyai Watanabe (Hymenoptera: Braconidae) is a specialist larval parasitoid of Mythimna separata Walker (Lepidoptera: Noctuidae). Cotesia kariyai wasps use herbivore‐induced plant volatiles (HIPVs) to locate hosts. However, complex natural habitats are full of volatiles released by both herbivorous host‐ and non‐host‐infested plants at various levels of intensity. Therefore, the presence of non‐hosts may affect parasitoid decisions while foraging. Here, the host‐finding efficiency of naive C. kariyai from HIPVs influenced by host‐ and non‐host‐infested maize [Zea mays L. (Poaceae)] plants was investigated with a four‐arm olfactometer. Ostrinia furnacalis Guenée (Lepidoptera: Crambidae) was selected as a non‐host species. One unit (1 U) of host‐ or non‐host‐infested plant was prepared by infesting a potted plant with five host or seven non‐host larvae. In two‐choice bioassays, host‐infested plants fed upon by different numbers of larvae, and various units of host‐ and non‐host‐infested plants (infestation units; 1 U, 2 U, and 3 U) were arranged to examine the effects of differences in volatile quantity and quality on the olfactory responses of C. kariyai with the assumption that volatile quantity and quality changes with differences in numbers of insects and plants. Cotesia kariyai was found to perceive quantitative differences in volatiles from host‐infested plants, preferring larger quantities of volatiles from larger numbers of larvae or plants. Also, the parasitoids discriminated between healthy plants, host‐infested plants, and non‐host‐infested plants by recognising volatiles released from those plants. Cotesia kariyai showed a reduced preference for host‐induced volatiles, when larger numbers of non‐host‐infested plants were present. Therefore, quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested plants appear to affect the decision of C. kariyai during host‐habitat searching in multiple tritrophic systems.     

Sex‐specific responses of Asian citrus psyllid to volatiles of conspecific and host‐plant origin

Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is the primary vector of Candidatus Liberibacter spp. bacteria that cause citrus greening, a disease of worldwide importance. Olfactometry was employed to test responses of D. citri to odours from intact citrus plants (Mexican lime, Citrus aurantifolia, sour orange, Citrus aurantium, Marsh grapefruit, Citrus paradisi and Valencia orange, Citrus sinensis), citrus plants previously infested with D. citri, and odours of conspecifics including nymphs, adult insects of same and opposite sex, and their products (honeydew), both alone and in combination. In contrast to other studies, psyllids of both sexes were attracted to volatiles of undamaged Mexican lime leaves, whereas undamaged grapefruit attracted only females, and leaves of Valencia and sour orange did not attract either sex. All four plant species attracted female psyllids when previously infested, but only Mexican lime and sour orange‐attracted males. Thus, Citrus species appear to vary in the production of both constituitive and induced volatiles that attract adult psyllids. Volatiles emitted by nymphs did not attract either sex, but psyllid honeydew was attractive to males, likely due to female pheromone residues. Males oriented to the odour of females, whereas the reverse was not true, and neither males nor females oriented to same‐sex volatiles. The addition of conspecific cues (adults, nymphs or honeydew) did not increase female attraction to previously infested leaves, but male response was increased by the presence of adults and honeydew, regardless of plant species. Thus, female psyllids appear to orient more strongly to volatiles of plant origin, whereas males respond more strongly to cues emanating from females and conspecific excretions. These results suggest that female psyllids drive the initial colonization of host plants, whereas males orient to females and infested plants. Identification of the specific volatiles involved may permit their use in monitoring and management of this pest.     

Variability and stability of tea weevil‐induced volatile emissions from tea plants with different weevil densities,photoperiod and infestation duration

Abstract After herbivore attack, many plants emit herbivore‐induced plant volatiles (HIPVs). HIPVs can attract carnivores and/or repel herbivores, thereby mediating tritrophic plant–herbivore–carnivore interactions. HIPVs act as chemical information between organisms; hence, their variability and stability are vital. In the present study, variations in the volatile emissions, from the tea plant Camellia sinensis (O. Ktze) damaged by the tea weevil Myllocerinus aurolineatus (Voss) (Coleoptera: Curculionidae), with weevil densities, photoperiod and infestation duration, were investigated. The volatiles induced by high‐density weevils were more abundant in composition and amount than those induced by low‐density weevils, whether at noon, night or after weevil removal. The induced volatile emissions were similar on the second and third day after infestation, and the emissions of the major induced compounds displayed diurnal cycles. Linalool, (E,E)‐α‐farnesene, and benzyl nitrile were emitted mainly at noon, whereas 1,3,8‐p‐menthatriene and (E)‐β‐ocimene were maximally emitted at night. Given the different emission dynamics, significant differences were found between noon‐ and night‐induced volatiles. In summary, tea plants damaged by different weevil densities emitted a relatively stable signal at a particular time. This stability could be attributed to the similarities under the two densities of the main induced volatile compounds, their relative ratios and the emission dynamics of the induced volatiles.     

Associative learning of host presence in non‐host environments influences parasitoid foraging

1. Parasitoids are known to utilise learning of herbivore‐induced plant volatiles (HIPVs) when foraging for their herbivorous host. In natural situations these hosts share food plants with other, non‐suitable herbivores (non‐hosts). Simultaneous infestation of plants by hosts and non‐hosts has been found to result in induction of HIPVs that differ from host‐infested plants. Each non‐host herbivore may have different effects on HIPVs when sharing the food plant with hosts, and thus parasitoids may learn that plants with a specific non‐host herbivore also contain the host. 2. This study investigated the adaptive nature of learning by a foraging parasitoid that had acquired oviposition experience on a plant infested with both hosts and different non‐hosts in the laboratory and in semi‐field experiments. 3. In two‐choice preference tests, the parasitoid Cotesia glomerata shifted its preference towards HIPVs of a plant–host–non‐host complex previously associated with an oviposition experience. It could, indeed, learn that the presence of its host is associated with HIPVs induced by simultaneous feeding of its host Pieris brassicae and either the non‐host caterpillar Mamestra brassicae or the non‐host aphid Myzus persicae. However, the learned preference found in the laboratory did not translate into parasitisation preferences for hosts accompanying non‐host caterpillars or aphids in a semi‐field situation. 4. This paper discusses the importance of learning in parasitoid foraging, and debates why observed learned preferences for HIPVs in the laboratory may cancel out under some field experimental conditions.     

Antagonism between herbivore‐induced plant volatiles and trichomes affects tritrophic interactions

We used tomato genotypes deficient in the jasmonic acid (JA) pathway to study the interaction between the production of herbivore‐induced plant volatiles (HIPVs) that serve as information cues for herbivores as well as natural enemies of herbivores, and the production of foliar trichomes as defence barriers. We found that jasmonic acid‐insensitive1 (jai1) mutant plants with both reduced HIPVs and trichome production received higher oviposition of adult leafminers, which were more likely to be parasitized by the leafminer parasitoids than JA biosynthesis spr2 mutant plants deficient in HIPVs but not trichomes. We also showed that the preference and acceptance of leafminers and parasitoids to trichome‐removed plants from either spr2 or wild‐type (WT) genotypes over trichome‐intact genotypes can be ascribed to the reduced trichomes on treated plants, but not to altered direct and indirect defence traits such as JA, proteinase inhibitor (PI)‐II and HIPVs levels. Although the HIPVs of WT plants were more attractive to adult insects, the insects preferred trichome‐free jai1 plants for oviposition and also had greater reproductive success on these plants. Our results provide strong evidence that antagonism between HIPV emission and trichome production affects tritrophic interactions. The interactions among defence traits are discussed.     

Constitutive exposure to the volatile methyl salicylate reduces per‐capita foraging efficiency of a generalist predator to learned prey associations

Understanding the factors that influence the ability of predators to find and kill herbivores is central to enhancing their impact on prey populations, but few studies have tested the impact of these factors on predation rates in realistic foraging environments. Using the tri‐trophic system consisting of tomato, Solanum lycopersicum L. (Solanaceae), hornworm caterpillars, Manduca sexta L. (Lepidoptera: Sphingidae), and the predaceous stink bug Podisus maculiventris (Say) (Hemiptera: Pentatomidae), we measured the effects of associative learning and plant volatile camouflage on predator behavior and foraging efficiency in field enclosures. To do so, we compared experienced vs. naive individuals under varying environmental contexts. Experienced predators were those with prior exposure to induced volatiles from the tomato–caterpillar association, whereas naive predators had not experienced tomato, only prey (caterpillars). We varied their environmental foraging matrix using either (1) tomato surrounded by basil (Ocimum basilicum L.; Lamiaceae) or (2) tomato exposed to the synthetic volatile, methyl salicylate (MeSA). We found that (1) experienced predators were more efficient than naive predators, capturing 28% more prey; (2) the tomato–basil combination did not affect predator–prey interactions; and (3) constitutive emission of synthetic MeSA caused a 22% reduction in P. maculiventris predation rate. These differences corresponded with distinct shifts in predator foraging; for example, experienced individuals were less stationary and exhibited unique behaviors such as stylet extension. Taken together, these results suggest that it is possible to improve the function of generalist predators in suppressing prey by coupling odors with food. However, constitutive emission of volatiles to attract natural enemies may ultimately camouflage neighboring plants, reducing the benefits of orientation to learned stimuli such as induced volatiles.     

Genetic mapping shows intraspecific variation and transgressive segregation for caterpillar‐induced aphid resistance in maize

Plants in nature have inducible defences that sometimes lead to targeted resistance against particular herbivores, but susceptibility to others. The metabolic diversity and genetic resources available for maize (Zea mays) make this a suitable system for a mechanistic study of within‐species variation in such plant‐mediated interactions between herbivores. Beet armyworms (Spodoptera exigua) and corn leaf aphids (Rhopalosiphum maidis) are two naturally occurring maize herbivores with different feeding habits. Whereas chewing herbivore‐induced methylation of 2,4‐dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one glucoside (DIMBOA‐Glc) to form 2‐hydroxy‐4,7‐dimethoxy‐1,4‐benzoxazin‐3‐one glucoside (HDMBOA‐Glc) promotes caterpillar resistance, lower DIMBOA‐Glc levels favour aphid reproduction. Thus, caterpillar‐induced DIMBOA‐Glc methyltransferase activity in maize is predicted to promote aphid growth. To test this hypothesis, the impact of S. exigua feeding on R. maidis progeny production was assessed using seventeen genetically diverse maize inbred lines. Whereas aphid progeny production was increased by prior caterpillar feeding on lines B73, Ki11, Ki3 and Tx303, it decreased on lines Ky21, CML103, Mo18W and W22. Genetic mapping of this trait in a population of B73 × Ky21 recombinant inbred lines identified significant quantitative trait loci on maize chromosomes 1, 7 and 10. There is a transgressive segregation for aphid resistance, with the Ky21 alleles on chromosomes 1 and 7 and the B73 allele on chromosome 10 increasing aphid progeny production. The chromosome 1 QTL coincides with a cluster of three maize genes encoding benzoxazinoid O‐methyltransferases that convert DIMBOA‐Glc to HDMBOA‐Glc. Gene expression studies and benzoxazinoid measurements indicate that S. exigua ‐induced responses in this pathway differentially affect R. maidis resistance in B73 and Ky21.     

Addition of terpenoids to pear ester plus acetic acid increases catches of codling moth (Lepidoptera: Tortricidae)

Field studies were conducted to evaluate new kairomone blends in combination with pear ester (E,Z)‐2,4‐ethyl decadienoate (PE) and acetic acid (AA) for their attraction of male and female codling moth, Cydia pomonella (L.), in apple, Malus domestica Borkhausen. The addition of decanal to either AA or PE alone significantly increased total and female moth catches. However, the addition of decanal did not improve the attraction of PE + AA. The addition of either the pyranoid (PyrLOX) or furanoid (FurLOX) linalool oxide but not linalool (LOL) increased moth catches with PE but did not increase catches with PE + AA. Similarly, the addition of PyrLOX plus decanal did not improve PE + AA. The addition of (E)‐4,8‐dimethyl‐1,3,7‐nonatriene (DMNT) to either AA, PE + AA or PE + AA+decanal did not significantly increase moth catches. However, the addition of PyrLOX to traps with PE + AA and DMNT (4‐component lure) significantly increased moth catches compared with PE + AA alone or any of the ternary blends of these volatiles. Females accounted for 60%–80% of the total catch with this 4‐component lure. The 4‐component blend with PyrLOX was a more attractive lure than similar blends that substituted LOL, or a binary blend of LOL and FurLOX for PyrLOX. The 4‐component blend caught nearly fourfold more total and female moths than the purported attractant N‐butyl sulphide when it was used in combination with PE + AA. These results indicate that significant improvements in monitoring, mating disruption and mass trapping of codling moth are possible. Further studies are needed to assess the new attractive blend's effectiveness in combination with sex pheromone lures and to evaluate whether other host plant volatiles can be added or substitute for DMNT or LOX when used in combination with PE + AA.     

Over what distance are plant volatiles bioactive? Estimating the spatial dimensions of attraction in an arthropod assemblage

As studies demonstrating attraction of natural enemies to synthetic herbivore‐induced plant volatiles (HIPVs) accumulate, it is becoming increasingly important to investigate how deployment of these compounds influences arthropod behavior and distribution in the field. There is currently an unexplained dichotomy in the literature regarding the distance over which HIPVs are thought to be effective. It is assumed that these compounds increase recruitment of natural enemies into fields, whereas experiments have found the effects of attraction to dissipate as little as 1.5 m from lures. Through the use of the common HIPV phenylethyl alcohol in soybean [Glycine max (L.) Merr (Fabaceae)] fields, we used replicated mini plots to test the spatial scale and consequences of attraction by analyzing the response of a complex arthropod community to HIPVs along a distance gradient from the HIPV source. Although repellent effects were more common than attractive ones, we found that insect responses to HIPVs are generally consistent out to a range of 8 m, corroborating the idea that volatiles can influence a wide area and are capable of increasing arthropod recruitment at a field scale. Evidence of redistribution (i.e., depletion of patches surrounding HIPV‐augmented plots) was found for a single taxon, braconid wasps, for which augmentation occurred around the lure, but with a reciprocal decline in abundance at greater distances from the emission site. These results are both encouraging and cautionary. Although broad‐scale diffusion of HIPVs appears to be common, redistribution of key predators and/or parasitoids may complicate natural enemy management on a landscape scale by aggravating pest outbreaks in areas robbed of their normal carnivore assemblage.     

What signals do herbivore-induced plant volatiles provide conspecific herbivores?

Herbivore-induced plant volatiles (HIPVs) have been opined as ‘indirect or direct defenses’ of plants and are extensively studied. In contrast, HIPVs may also indicate that plant defenses have been overcome by herbivores infesting the plant; however, studies on this aspect have so far received little attention. Using the interaction of Capsicum annum (Bell pepper) with its pest Scirtothrips dorsalis (Chilli thrips) as a model system, we studied the role of HIPVs in this selected insect–plant interaction. Multiple-choice olfactometer assays with headspace volatiles collected from different growth stages of un-infested C. annum plants represented by pre-flowering (PF), flowering (FL) and fruiting stages (FR) proved FR volatiles to be highly attractive to S. dorsalis. Further, FR plants were infested with S. dorsalis adults and HIPVs released by infested plants were collected and subjected to multiple-choice olfactometer bioassays. Thrips were significantly attracted to HIPVs than to headspace volatiles of un-infested FR plants or thrips body odour. Coupled GC-EAG with S. dorsalis and HIPVs or FR plant volatile revealed specific compounds that elicited an EAG response. Individual EAG-active compounds were less attractive to thrips, however, synthetic blends of EAG-active compounds at the ratio similar to headspace samples were found to be highly attractive. However, when given a choice between synthetic blends of HIPVs and FR, thrips were significantly attracted to synthetic blend of HIPVs. Our study provides empirical data on signals HIPVs may provide to conspecific herbivores and suggests that the role of HIPVs, mostly generalized as defense, may vary based on the interaction and must be studied closely to understand their ecological functions.     

Effects of single and multiple herbivory by host and non‐host caterpillars on the attractiveness of herbivore‐induced volatiles of sugarcane to the generalist parasitoid Cotesia flavipes

It is well known that parasitoids are attracted to volatiles emitted by host‐damaged plants; however, this tritrophic interaction may change if plants are attacked by more than one herbivore species. The larval parasitoid Cotesia flavipesCameron (Hymenoptera: Braconidae) has been used intensively in Brazil to control the sugarcane borer, Diatraea saccharalisFabricius (Lepidoptera: Pyralidae) in sugarcane crops, where Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), a non‐stemborer lepidopteran, is also a pest. Here, we investigated the ability of C. flavipes to discriminate between an unsuitable host (S. frugiperda) and a suitable host (D. saccharalis) based on herbivore‐induced plant volatiles (HIPVs) emitted by sugarcane, and whether multiple herbivory (D. saccharalis feeding on stalk + S. frugiperda feeding on leaves) in sugarcane affected the attractiveness of HIPVs to C. flavipes. Olfactometer assays indicated that volatiles of host and non‐host‐damaged plants were attractive to C. flavipes. Even though host‐ and non‐host‐damaged plants emitted considerably different volatile blends, neither naïve nor experienced wasps discriminated suitable and unsuitable hosts by means of HIPVs emitted by sugarcane. With regard to multiple herbivory, wasps innately preferred the odor blend emitted by sugarcane upon non‐host + host herbivory over host‐only damaged plants. Multiple herbivory caused a suppression of some volatiles relative to non‐host‐damaged sugarcane that may have resulted from the unaltered levels of jasmonic acid in host‐damaged plants, or from reduced palatability of host‐damaged plants to S. frugiperda. In conclusion, our study showed that C. flavipes responds to a wide range of plant volatile blends, and does not discriminate host from non‐host and non‐stemborer caterpillars based on HIPVs emitted from sugarcane. Moreover, we showed that multiple herbivory by the sugarcane borer and fall armyworm increases the attractiveness of sugarcane plants to the parasitoids.     

Inter‐kingdom signaling — symbiotic yeasts produce semiochemicals that attract their yellowjacket hosts

In recent studies, the yeast species Hanseniaspora uvarum and Lachancea thermotolerans were isolated from the digestive tract of four North American yellowjacket species (Hymenoptera: Vespidae), and attraction of yellowjackets to brewer's yeast, Saccharomyces cerevisiae (all Saccharomycetaceae), growing on fruit powder was demonstrated. We tested the hypothesis that Vespula spp. are attracted to cultures of H. uvarum and L. thermotolerans and their respective volatiles. In field experiments, we found that H. uvarum and L. thermotolerans are attractive to three species of yellowjacket, but only when grown on grape juice‐infused yeast peptone dextrose (YPD) agar. Using gas chromatography‐mass spectrometry, we analyzed the headspace volatiles produced by these yeasts, and field tested an 18‐component yeast synthetic semiochemical blend. This synthetic blend attracted western yellowjackets, Vespula pensylvanica (Saussure), but no other yellowjacket species. Acetic acid or ethanol added to the synthetic blend at biologically relevant doses either had no effect or significantly lowered trap captures. Our results demonstrate that yeast symbionts isolated from the digestive tract of yellowjackets are attractive to their hosts. Further research is needed to identify the volatiles mediating attraction of species other than V. pensylvanica to the yeast cultures.     

Interactions between a pollinating seed predator and its host plant: the role of environmental context within a population

Plant–insect interactions often are important for plant reproduction, but the outcome of these interactions may vary with environmental context. Pollinating seed predators have positive and negative effects on host plant reproduction, and the interaction outcome is predicted to vary with density or abundance of the partners. We studied the interaction between Silene stellata, an herbaceous perennial, and Hadena ectypa, its specialized pollinating seed predator. Silene stellata is only facultatively dependent upon H. ectypa for pollination because other nocturnal moth co‐pollinators are equally effective at pollen transfer. We hypothesized that for plants without conspecific neighbors, H. ectypa would have higher visitation rates compared to co‐pollinators, and the plants would experience lower levels of H. ectypa pollen deposition. We predicted similar oviposition throughout the study site but greater H. ectypa predation in the area without conspecific neighbors compared to plants embedded in a naturally high density area. We found that H. ectypa had consistently higher visitation than moth co‐pollinators in all host plant contexts. However, H. ectypa pollinator importance declined in areas with low conspecific density because of reduced pollen deposition, resulting in lower seed set. Conversely, oviposition was similar across the study site independent of host plant density. Greater likelihood of very high fruit predation combined with lower pollination by H. ectypa resulted in reduced S. stellata female reproductive success in areas with low conspecific density. Our results demonstrate local context dependency of the outcomes of pollinating seed predator interactions with conspecific host plant density within a population.     

Host plant volatiles responsible for the invasion of Stenotus rubrovittatus (Heteroptera: Miridae) into paddy fields

We investigated the attractiveness of synthetic volatile blends or individual volatiles of flowering rice panicles or flowering Scirpus juncoides spikelets to the sorghum plant bug Stenotus rubrovittatus (Matsumura). None of the individual chemicals tested attracted either sex of the bug. Synthetic volatile blends of flowering rice panicles composed of geranyl acetone, β‐caryophyllene, n‐decanal, methyl salicylate, β‐elemene and n‐tridecene attracted females. The synthetic blend of volatiles was just as attractive as natural flowering rice panicles to females. Other synthetic blends did not attract the bug. We sampled headspace volatiles from flowering S. juncoides spikelets with solid‐phase microextraction and analysed them using gas chromatography–mass spectrometry. The main volatile emitted from S. juncoides was β‐caryophyllene, one of the major volatile components of flowering rice panicles. β‐Elemene was a common volatile found in flowering rice panicles and flowering S. juncoides spikelets. Therefore, we investigated the attractiveness of synthetic blends of flowering rice panicles and S. juncoides spikelets composed of β‐caryophyllene and β‐elemene. The synthetic blend of flowering S. juncoides spikelets significantly attracted males but not females. The synthetic blend of flowering rice panicles composed of β‐caryophyllene and β‐elemene did not attract either sex. These results suggest that β‐caryophyllene and β‐elemene are common active compounds responsible for attractiveness of flowering rice panicles and S. juncoides spikelets although some of the other volatile components act synergistically with these two compounds in natural plant odours.     

The maize lipoxygenase,ZmLOX10, mediates green leaf volatile,jasmonate and herbivore‐induced plant volatile production for defense against insect attack

Fatty acid derivatives are of central importance for plant immunity against insect herbivores; however, major regulatory genes and the signals that modulate these defense metabolites are vastly understudied, especially in important agro‐economic monocot species. Here we show that products and signals derived from a single Zea mays (maize) lipoxygenase (LOX), ZmLOX10, are critical for both direct and indirect defenses to herbivory. We provide genetic evidence that two 13‐LOXs, ZmLOX10 and ZmLOX8, specialize in providing substrate for the green leaf volatile (GLV) and jasmonate (JA) biosynthesis pathways, respectively. Supporting the specialization of these LOX isoforms, LOX8 and LOX10 are localized to two distinct cellular compartments, indicating that the JA and GLV biosynthesis pathways are physically separated in maize. Reduced expression of JA biosynthesis genes and diminished levels of JA in lox10 mutants indicate that LOX10‐derived signaling is required for LOX8‐mediated JA. The possible role of GLVs in JA signaling is supported by their ability to partially restore wound‐induced JA levels in lox10 mutants. The impaired ability of lox10 mutants to produce GLVs and JA led to dramatic reductions in herbivore‐induced plant volatiles (HIPVs) and attractiveness to parasitoid wasps. Because LOX10 is under circadian rhythm regulation, this study provides a mechanistic link to the diurnal regulation of GLVs and HIPVs. GLV‐, JA‐ and HIPV‐deficient lox10 mutants display compromised resistance to insect feeding, both under laboratory and field conditions, which is strong evidence that LOX10‐dependent metabolites confer immunity against insect attack. Hence, this comprehensive gene to agro‐ecosystem study reveals the broad implications of a single LOX isoform in herbivore defense.