Host Finding Cues Research Articles

Functional characterization of an olfactory receptor in the Oriental fruit fly, Bactrocera dorsalis, that responds to eugenol and isoeugenol.

Most insects utilize a diverse array of olfactory cues for host finding and reproduction behaviors. Males of several Dacini fruit fly species (Tephritidae) are selectively attracted to certain phytochemicals to acquire sex pheromone precursors. Despite the importance of olfaction, only a limited number of olfactory receptors (ORs) in Dacini fruit flies have been characterized. In this study, I focused on the OR94b-2 subfamily, because a clade consisting of these homologs was distinctly localized from other OR clades in a constructed phylogenetic tree. To deorphanize the ORs, I used plant essential oils to screen ligands. Using heterologous expression in Xenopus oocytes, I analyzed the functional properties of BdorOR94b-2 and ZcucOR94b-2 from the Oriental fruit fly, Bactrocera dorsalis, and the melon fruit fly, Zeugodacus cucurbitae, respectively. I found that cinnamon leaf oil evoked responses in oocytes expressing BdorOR94b-2 and the corresponding co-receptor BdorORCO. Gas chromatography-mass spectrometry analysis indicated that eugenol is a major component of cinnamon leaf oil. In accordance with the response to cinnamon leaf oil containing eugenol, BdorOR94b-2/BdorORCO revealed a weak but significant response to eugenol. BdorOR94b-2/BdorORCO also responded to isoeugenol, but not to other related aromatic semiochemicals such as known male-specific attractants and sex pheromones. In contrast, ZcucOR94b-2/ZcucORCO did not respond to any of the phenolic compounds tested, including eugenol analogs. Therefore, BdorOR94b-2/BdorORCO is narrowly tuned to eugenol analogs, whereas ZcucOR94b-2/ZcucORCO likely binds to other compound(s).

Can Anastatus bifasciatus Be Used for Augmentative Biological Control of the Brown Marmorated Stink Bug in Fruit Orchards?

The generalist egg parasitoid Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) is the most prevalent egg parasitoid of the invasive Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) in Europe. To assess its efficacy against the pest H. halys and to validate the potential risks for non-target species in a realistic field setting, inundative releases were conducted over three consecutive years in four fruit orchards in Switzerland and Italy. In total, more than 4300 A. bifasciatus females were released, which was equivalent to 11,000 to 26,000 females per hectare, depending on distances between trees in each orchard. Parasitism of freeze-killed sentinel H. halys eggs achieved with the current release strategy was on average 6% (range: 2%–16%) and considered not high enough to effectively suppress the pest. However, the overall impact of A. bifasciatus on the mortality of H. halys eggs was likely underestimated. If pre-imaginal parasitoid mortality (3.3%) and host feeding (6%) are added to the observed parasitism (6%), the actual induced mortality of H. halys eggs may reach more than 15%. Parasitism of lepidopteran non-target species reached an average of 8% and thus, some degree of non-target parasitism after mass releases may be expected. To quantify the impact of the parasitoids in the orchards more precisely, naturally laid egg masses should be used in future trials to include host-finding cues of the host and host plants, and larger scale releases with potentially higher densities of parasitoids should be considered.

Dealing with food shortage: larval dispersal behaviour and survival on non‐prey food of the hoverfly Episyrphus balteatus

1. Predatory larvae often have to face food shortages during their development, and thus the ability to disperse and find new feeding sites is crucial for survival. However, the dispersal capacity of predatory larvae, the host finding cues employed, and their use of alternative food sources are largely unknown. These aspects of the foraging behaviour of the aphidophagous hoverfly (Episyrphus balteatus De Geer) larvae were investigated in the present study.2. It was shown that these hoverfly larvae do not leave a plant as long as there are aphids available, but that dispersing larvae are able to find other aphid colonies in the field. Dispersing hoverfly larvae accumulated on large aphid colonies, but did not distinguish between different pea aphid race–plant species combinations. Large aphid colonies might be easier to detect because of intensified searching by hoverfly larvae following the encounter of aphid cues like honeydew that accumulate around large colonies.3. It was further shown that non‐prey food, such as diluted honey or pollen, was insufficient for hoverfly larvae to gain weight, but prolonged the survival of the larvae compared with unfed individuals. As soon as larvae were switched back to an aphid diet, they rapidly gained weight and some pupated after a few days. Although pupation and adult hatching rates were strongly reduced compared with hoverflies continuously fed with aphids, the consumption of non‐prey food most probably increases the probability that hoverfly larvae find an aphid colony and complete their development.

Olfactory host‐finding behaviour of Oulema melanopus (Coleoptera: Chrysomelidae) and its parasitoid, Tetrastichus julis (Hymenoptera: Eulophidae)

AbstractBehavioural responses to the host‐associated olfactory cues have not been completely understood for the cereal leaf beetle, Oulema melanopus, and its principal parasitoid, Tetrastichus julis. We, therefore, investigated the role of olfactory cues in the host‐finding behaviour of these species using olfactory bioassays. Behavioural responses of O. melanopus to odours emanating from intact host plants (wheat, oat, barley) vs. a clean‐air control were tested using multichoice and two‐choice bioassays. For T. julis, responses of naïve and experienced adult female wasps to odours associated with the faecal coat of O. melanopus larvae were measured under multichoice and two‐choice conditions. Our results indicate that olfactory cues are involved in the host‐finding behaviour of both O. melanopus and T. julis. Olfactory responses of O. melanopus were influenced by the sex of the beetle and the physiological stage of adults (reproductively active vs. in reproductive diapause). Females respond to olfactory cues in greater proportions than males, and reproductively active, overwintered adults show greater responsiveness than teneral adults in reproductive diapause. Behavioural responses to cues emanating from different crop species were different in multichoice bioassays but not in two‐choice bioassays. Further, we report for the first time that the olfactory cues associated with the faecal coat of O. melanopus evoke host‐finding behaviour of its parasitoid, T. julis. Naïve female wasps are more likely to use these cues to locate the potential host than experienced females. The results of this investigation provide insights into host finding by both the species and the nature of behavioural response brought about by olfactory stimuli, and the results can help to design strategies to improve parasitoid activity by enhancing the crop environment to generate cues for host finding and to manage O. melanopus populations.

Antennal transcriptome and differential expression of olfactory genes in the yellow peach moth, Conogethes punctiferalis (Lepidoptera: Crambidae).

The yellow peach moth (YPM), Conogethes punctiferalis (Guenée), is a multivoltine insect pest of crops and fruits. Antennal-expressed receptors are important for insects to detect olfactory cues for host finding, mate attraction and oviposition site selection. However, few olfactory related genes were reported in YPM until now. In the present study, we sequenced and characterized the antennal transcriptomes of male and female YPM. In total, 15 putative odorant binding proteins (OBPs), 46 putative odorant receptors (ORs) and 7 putative ionotropic receptors (IRs) were annotated and identified as olfactory-related genes of C. punctiferalis. Further analysis of RT-qPCR revealed that all these olfactory genes are primarily or uniquely expressed in male and female antennae. Among which, 3 OBPs (OBP4, OBP8 and PBP2) and 4 ORs (OR22, OR26, OR44 and OR46) were specially expressed in male antennae, whereas 4 ORs (OR5, OR16, OR25 and OR42) were primarily expressed in female antennae. The predicted protein sequences were compared with homologs in other lepidopteran species and model insects, which showed high sequence homologies between C. punctiferalis and O. furnacalis. Our work allows for further functional studies of pheromone and general odorant detection genes, which might be meaningful targets for pest management.

Attractiveness of volatiles from different body parts to the malaria mosquito Anopheles coluzzii is affected by deodorant compounds.

Mosquitoes display biting preferences among different sites of the human body. In addition to height or convection currents, body odour may play a role in the selection of these biting sites. Previous studies have shown that skin emanations are important host-finding cues for mosquitoes. In this study, skin emanations were collected from armpits, hands and feet; the volatile profiles were analysed and tested for their attractiveness to the malaria mosquito Anopheles coluzzii. Skin emanations collected from armpits were less attractive to An. coluzzii compared to hands or/and feet. The difference may have been caused by deodorant residues, which were found in the armpit samples and not in those of hands and feet. In a subsequent experiment, volunteers were asked to avoid using skincare products for five days, and thereafter, no differences in attractiveness of the body parts to mosquitoes were found. The detected deodorant compound isopropyl tetradecanoate inhibited mosquito landings in a repellent bioassay. It is concluded that the volatiles emanated from different body parts induced comparable levels of attraction in mosquitoes, and that skincare products may reduce a person’s attractiveness to mosquitoes.

Volatiles released by Chinese liquorice roots mediate host location behaviour by neonate Porphyrophora sophorae (Hemiptera: Margarodidae).

The cochineal scale, Porphyrophora sophorae (Hemiptera: Coccoidea, Margarodidae), is one of the most serious arthropod pests of Chinese liquorice, Glycyrrhiza uralensis (Fabaceae), an important medicinal herb. The adult females tend to deposit the ovisacs in soil relatively far away from liquorice plants. After hatching, neonates move out of the soil and may use chemical cues to search for new hosts. We collected and analysed the volatiles from soils with and without liquorice roots, and chromatographic profiles revealed hexanal, β-pinene and hexanol as potential host-finding cues for P. sphorae. The attractiveness of these compounds to neonates was studied in the laboratory using four-arm olfactometer bioassays. The larvae showed a clear preference for β-pinene over hexanal and hexanol, as well as all possible combinations of the three compounds. In addition, a field experiment confirmed that β-pinene was significantly more attractive than hexanal and hexanol. Newly eclosed larvae of P. sphorae exploit root volatiles as chemical cues to locate their host plant. β-Pinene proved to be the major chemical cue used by P. sphorae neonates searching for roots of their host plant. © 2016 Society of Chemical Industry.

Chemical ecology of insect-plant interactions: ecological significance of plant secondary metabolites.

Plants produce a diverse array of secondary metabolites as chemical barriers against herbivores. Many phytophagous insects are highly adapted to these allelochemicals and use such unique substances as the specific host-finding cues, defensive substances of their own, and even as sex pheromones or their precursors by selectively sensing, incorporating, and/or processing these phytochemicals. Insects also serve as pollinators often effectively guided by specific floral fragrances. This review demonstrates the ecological significance of such plant secondary metabolites in the highly diverse interactions between insects and plants.

PHOTOSELECTIVE NETS AND SCREENS CAN REDUCE INSECT PESTS AND DISEASES IN AGRICULTURAL CROPS

Insects use optical cues for host finding and flight orientation. The hue, brightness, size, shape and contrast of the visual cue affect the insect response. Manipulation of the natural optical cues can interfere with host finding and dispersal of insect pests. Sucking insect pests, such as aphids and whiteflies, cause great economic losses for growers of agricultural crops worldwide. These pests cause direct feeding damages and they often transmit viruses to crop plants. Non-persistent viruses must be transmitted within minutes to 2 hours after aphids acquired them. These insects have receptors for UV light (peak sensitivity at 360 nm) and for green-yellow light (peak sensitivity at 520-540 nm). The absence of UV deters these pests and decreases their dispersal rate. Yellow color induces landing and favors settling of these insects. High level of reflected sunlight (above 25% of sun radiation) deters landing of these insects. Thus, optical cues can be used to divert pests away from crop plants. This can be achieved by incorporating optical additives to cladding materials (plastic sheets, nets and screens above plants). For non-persistent viruses, any delay of the infected aphids with an arresting color can reduce the efficacy of viral transmission. Results of our studies indicate that optical manipulation can reduce the infestation levels of aphids and whiteflies and the incidence of viral diseases they transmit by 2-10 folds. Thus, optical manipulations can be a part of integrated pest management programs for protected crops.

Herbivore-Induced Plant Volatiles Can Serve as Host Location Cues for a Generalist and a Specialist Egg Parasitoid

Herbivore-induced plant volatiles are important host finding cues for larval parasitoids, and similarly, insect oviposition might elicit the release of plant volatiles functioning as host finding cues for egg parasitoids. We hypothesized that egg parasitoids also might utilize HIPVs of emerging larvae to locate plants with host eggs. We, therefore, assessed the olfactory response of two egg parasitoids, a generalist, Trichogramma pretiosum (Tricogrammatidae), and a specialist, Telenomus remus (Scelionidae) to HIPVs. We used a Y-tube olfactometer to tests the wasps' responses to volatiles released by young maize plants that were treated with regurgitant from caterpillars of the moth Spodoptera frugiperda (Noctuidae) or were directly attacked by the caterpillars. The results show that the generalist egg parasitoid Tr. pretiosum is innately attracted by volatiles from freshly-damaged plants 0-1 and 2-3h after regurgitant treatment. During this interval, the volatile blend consisted of green leaf volatiles (GLVs) and a blend of aromatic compounds, mono- and homoterpenes, respectively. Behavioral assays with synthetic GLVs confirmed their attractiveness to Tr. pretiosum. The generalist learned the more complex volatile blends released 6-7h after induction, which consisted mainly of sesquiterpenes. The specialist T. remus on the other hand was attracted only to volatiles emitted from fresh and old damage after associating these volatiles with oviposition. Taken together, these results strengthen the emerging pattern that egg and larval parasitoids behave in a similar way in that generalists can respond innately to HIPVs, while specialists seems to rely more on associative learning.

Diurnal and nocturnal herbivore induction on maize elicit different innate response of the fall armyworm parasitoid, Campoletis flavicincta

Herbivore-attacked plants produce specific volatile substances that represent important cues for host finding by natural enemies. The fall armyworm Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is a voracious herbivore and usually feed on maize in all periods of the day. Given that plant needs light to synthesize de novo herbivore-induced volatiles, volatile blend may be changed depending on time of the day the plant is induced, what could interfere in natural enemy foraging. In this sense, the current study aimed to investigate differential attractiveness of maize elicited by fall armyworm regurgitant under light and dark conditions to its specialist larval parasitoid Campoletis flavicincta (Ashmead) (Hymenoptera: Ichneumonidae). All bioassays were conducted in Y-tube olfactometer to assess parasitoid response to odors from undamaged maize, mechanical damage, and regurgitant-treated plants at 0–1, 5–6, and 24–25 h after induction. The results showed that naive wasps were attracted to volatiles emitted by nocturnal regurgitant-treated maize at 5–6 h, but not to odors from diurnal regurgitant-treated plants. The differential attractiveness is likely due to blend composition as nocturnal regurgitant-treated plants emit aromatic compounds and the homoterpene (3E)-4,8-dimethyl-1,3,7-nonatriene in larger amounts than diurnal-treated plants.

Hide and seek in forests: colonization by the pine processionary moth is impeded by the presence of nonhost trees

The disruption of host‐finding cues has been proposed as a key mechanism underlying the lower damage caused by phytophagous insects in mixed forests. We tested this hypothesis by investigating the distribution of pine processionary moth Thaumetopoea pityocampa (Denis & Schiffer‐Müller) (Lepidoptera) infestation at the edges of pure stands of Pinus pinaster (AÏton) at some distance from nonhost trees (Experiment 1) or bordered in part by a broadleaved hedgerow (Experiment 2). An ‘edge effect' was demonstrated, with trees at the edge of the stand being more heavily infested than those at the interior of the stand. The presence of a nonhost broadleaved hedgerow in front of the edge of the pine stand resulted in lower T. pityocampa infestation. There were significantly fewer T. pityocampa nests behind the hedgerow than on the exposed part of the edge. The presence of the hedgerow did not dilute or repel T. pityocampa infestation further into the pine stand, although it decreased the infestation of T. pityocampa throughout the pine stand. The decrease in T. pityocampa infestation behind the hedgerow was greater when the broadleaved hedgerow was taller than the pine trees. These results highlight the benefits of using nonhost tree species on the edge of monospecific forest stands to reduce insect damage. This approach could be promoted as an innovative forest pest management method.

Comparative Innate Responses of the Aphid Parasitoid Diaeretiella rapae to Alkenyl Glucosinolate Derived Isothiocyanates, Nitriles, and Epithionitriles

Cruciferous plants (Brassicaceae) are characterized by the accumulation of a group of secondary metabolites known as glucosinolates that, following attack by pathogens or herbivores, may be hydrolyzed to one of a number of products including isothiocyanates and nitriles. Despite the range of hydrolysis products that may be produced, the toxicity of glucosinolates to pathogens and herbivores may be explained largely by the production of isothiocyanates. Isothiocyanates are also known to provide an indirect defense by acting as host finding cues for parasitoids of insect herbivores that attack crucifers. It has been speculated that nitriles may provide a similar indirect defense. Here, we investigate the olfactory perception and orientation behavior of the aphid parasitoid Diaeretiella rapae, to a range of alkenylglucosinolate hydrolysis products, including isothiocyanates, nitriles, and epithionitriles. Electroantennogram responses indicated peripheral odor perception in D. rapae females to all 3-butenylglucosinolate hydrolysis products tested. By contrast, of the 2-propenylglucosinolate hydrolysis products tested, only the isothiocyanate elicited significant responses. Despite showing peripheral olfactory detection of a range of 3-butenylglucosinolate hydrolysis products, naïve females oriented only to the isothiocyanate. Similarly, parasitoids oriented to 3-isothiocyanatoprop-1-ene, but not to the corresponding nitrile or epithionitrile. However, by rearing D. rapae either on Brassica nigra, characterized by the accumulation of 2-propenylglucosinolate, or Brassica rapa var rapifera, characterized by the accumulation of 3-butenylglucosinolate, altered the innate response of parasitoids to 3-isothiocyanatoprop-1-ene and 4-isothiocyanatobut-1-ene. These results are discussed in relation to the defensive roles of glucosinolate hydrolysis products and the influence of the host plant on aphid parasitoid behavior.

Identification and Field Evaluation of Grape Shoot Volatiles Attractive to Female Grape Berry Moth (Paralobesia viteana)

Solid-phase microextraction (SPME) and gas chromatography coupled with electroantennographic detection (GC-EAD) were used to identify volatile compounds from shoots of riverbank grape (Vitis riparia) that attract the female grape berry moth (GBM, Paralobesia viteana). Consistent EAD activity was obtained for 11 chemicals: (Z)-3-hexen-1-yl acetate, (E)-linalool oxide, (Z)-linalool oxide, nonanal, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate, decanal, beta-caryophyllene, germacrene-D, and alpha-farnesene. In flight-tunnel tests that involved female GBM and rubber septa loaded with subsets of these 11 compounds, we found that both the 11-component blend and a seven-component blend, composed of (E)-linalool oxide, (Z)-linalool oxide, nonanal, (E)-4,8-dimethyl-1,3,7-nonatriene, decanal, beta-caryophyllene and germacrene-D, elicited equivalent levels of upwind flight as freshly cut grape shoots. The removal of any of the seven compounds from the seven-component blend resulted in a significant decrease in female upwind flight responses. In a field trial with these two synthetic blends, traps equipped with either blend captured more female GBM compared to traps baited with hexane only (control), although the number of females caught was generally low. There were no differences in the number of males captured among treatments. Although in flight-tunnel trials, moths readily flew upwind to both grape shoots and rubber septa loaded with the best lures, they landed on shoots but not on rubber septa. Coupled with relatively low field catches, this suggests that additional host finding cues need to be identified to improve trap efficacy.

Can mustard seed meal increase attacks by Aleochara spp. on Delia radicum in oilseed rape?

Responses to mustard seed meal of two parasitic beetles, Aleochara bipustulata and A. bilineata, were assessed by measuring levels of parasitism of Delia radicum puparia and of root damage to oilseed rape, and by pitfall trapping of the beetles. Levels of parasitism and trap catches of A. bipustulata were higher in meal-treated plots than in untreated control plots; however, there were no significant effects on A. bilineata, numbers of D. radicum in roots or on levels of root damage. Olfactometry confirmed the absence of response by A. bilineata and showed that A. bipustulata is attracted to volatiles released by dry or wet mustard seed meal. From GC–MS, the most abundant volatiles from mustard seed meal were limonene and structurally-similar compounds. These results are discussed with respect to mechanism of attraction, the host finding cues used by the major parasitoids of D. radicum, and the value of mustard seed meal for enhancing biological control.

Infestation of commercial bumblebee (Bombus impatiens) field colonies by small hive beetles (Aethina tumida)

Abstract 1. The small hive beetle, Aethina tumida, is a parasite of honeybee (Apis mellifera) colonies native to sub‐Saharan Africa and has become an invasive species. In North America the beetle is now sympatric with bumblebees, Bombus, not occurring in its native range. Laboratory studies have shown that small hive beetles can reproduce in bumblebee colonies but it was not known whether infestations occur in the field.2. For the first time, infestation of bumblebee colonies by small hive beetles was investigated in the field. Commercial Bombus impatiens colonies (n= 10) were installed in proximity to infested apiaries. Within 8 weeks, all colonies that were alive in the 5‐week observation period (n= 9) became naturally infested with adult small hive beetles and successful small hive beetle reproduction occurred in five colonies.3. In four‐square choice tests, the beetles were attracted to both adult bumblebee workers and pollen from bumblebee nests, suggesting that these odours may serve as cues for host finding.4. The data indicate that bumblebee colonies may serve as alternative hosts for small hive beetles in the field. To foster the conservation of these essential native pollinators, investigations on the actual impact of small hive beetles on wild bumblebee populations are suggested.

Exploitation of a Woody Host Plant and Cerambycid-Associated Volatiles as Host-Finding Cues by the Larger Grain Borer (Coleoptera: Bostrichidae)

We collected twigs of Lannea nigritiana (Sc. Elliot) Keay attacked by the girdling cerambycid Analeptes trifasciata F. in the Lama forest of central Benin, West Africa. Emergence data from A. trifasciata wood samples revealed a diverse insect fauna, which consisted of 27 primarily coleopteran species of 8 different families. More than 70% of the identified insects were bostrichids. We report an association of the exotic larger grain borer, Pmstephanits tnmcatiis (Horn), and its introduced natural enemy, the histerid predator Teretriosoma nigrescens Lewis, with twigs girdled by an indigenous cerambycid. We found more P. truncatus directly above the girdling site than elsewhere. P. truncatus is not attracted to volatiles emitted by adults or larvae of A. trifasciata but is significantly attracted to odors of cerambycid frass, as well as to girdled and mechanically damaged L. nigritiana twigs. We discuss these results with regard to the host-finding behavior of P. truncatus.

Effect of Terpenoids and Related Compounds on the Oviposition Behavior of the European Corn Borer, Ostrinia nubilalis (Lepidoptera: Pyralidae)

Twenty-eight volatile plant compounds and related analogs were evaluated in separate laboratory assays for mediation of oviposition behaviors of the female European corn borer, Ostrinia nubilalis. The compounds were acyclic and cyclic monoterpenes or sesquiterpenes or related compounds and possessed different functional groups, chain lengths, and molecular weights. The compounds varied in their effect on O. nubilalis oviposition behaviors, ranging from deterrents to stimulants. Cyclic sesquiterpenes generally stimulated oviposition by O. nubilalis, but several acyclic sesquiterpenes deterred oviposition. Individual compounds also may be used as cues for host finding by adult O. nubilalis. The compounds described in this study may serve as a guide for the creative design of safe, environmentally compatible control methods for the European corn borer, a destructive pest of many agricultural crops. Keywords: Terpenes; behavior; oviposition; Lepidoptera; Pyralidae

Sequestration of plant secondary compounds by butterflies and moths

A number of aposematic butterfly and moth species sequester toxic substances from their host plants. Some of these insects can detect the toxic compounds during food assessment. Some pipevine swallowtails use aristolochic acids among the host finding cues during oviposition and larval feeding and accumulate the toxins in the body tissues throughout all life stages. Likewise, a danaine butterfly,Idea leuconoe, which sequesters high concentrations of pyrrolizidine alkaloids in the body, lays eggs in response to the specific alkaloid components contained in the apocynad host. Insect species sharing the same poisonous host plants may differ in the degree of sequestration of toxins. Two closely ralated aposematic geometrid moth species,Arichanna gaschkevitchii andA. melanaria, sequester a series of highly toxic diterpenoids (grayanotoxins) in different degrees, while a cryptic geometrid species,Biston robstus, does not sequester the toxins, illustrating the diversity in adaptation mechanisms even within the same subfamily. By contrast, a number of lepidopteran species store the same compounds though feeding upon taxonomically diverse plant species. A bitter cyanoglycoside, sarmentosin, was characterised from several moth species in the Geometridae, Zygaenidae and Yponomeutidae, and from the apollo butterflies,Parnassius spp. (Papilionidae), although each species feeds on different groups of plants. Interspecific similarities and differences in life history and ecology are discussed in relation to variable characteristics of sequestration of plant compounds among these lepidopteran insects.

Olfactory Response of the Larvae of the Onion Fly, Hylemya antiqua MEIGEN (Diptera : Anthomyiidae) to Volatile Compounds

The olfactory responses of the larvae of the onion fly, Hylemya antiqua MEIGEN were investigated using thirty-three volatile compounds commonly found in plants and three sulfur compounds. Both first and third instar larvae of the onion fly responded to five alcohols : from propanol to heptanol, three aldehydes : from pentanal to heptanal, three fatty acids : from valeric acid to heptylic acid, twenty-one esters and three green leaf volatiles. The larvae of the onion fly may also make use of aliphatic alcohols, aldehydes, acids and esters other than sulfur compounds as the cues for host finding. To sulfur compounds, first instar larvae strongly responded but third instar larvae did not. The difference in larval food (artificial diet or onion bulbs) was not considered the reason for these diverse responses.