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.     

The Role of Chemical Cues in Host and Mate Location in the Pear Psylla Cacopsylla bidens (Homoptera: Psyllidae)

Chemical communication was shown to play a role in the pear psylla, Cacopsylla bidens. Electrophysiological (EAG) and behavioral responses were investigated in males and females pear psylla . Males were found to be attracted to females, and especially to those on host plants, but not to males, uninfested host plants, or plants infested with conspecific larvae. On the other hand, females were not attracted to males or females but displayed some attraction to host plants. Furthermore, females showed a preference for uninfested pear versus plants infested with conspecific larvae. The antennae of males gave highest electroantenographic response to volatiles from pears infested with females but not males, while females, responded also toward the volatiles of pear alone. These results indicate that females of C. bidens emit sex pheromones that are attractive to the males and suggest that, host volatiles may play a role in host selection by pear psylla females.     

Oviposition experience on a host-infested plant affects flight and antennal searching behavior of Cotesia kariyai toward the host-plant complex

The flight response of Cotesia kariyaiWatanabe (Hymenoptera: Braconidae), a parasitoid of the polyphagous herbivore, Mythimna separataWalker (Lepidoptera: Noctuidae), to pairs of different plant species infested by M. separatalarvae was tested under a dual choice condition in the laboratory. The oviposition-inexperienced (naive) wasps showed preference in the order: corn > kidney bean > Japanese radish. Wasps that had previously oviposited on the less preferred plant in a pair were found to have shifted their preference to this plant at 2 h after oviposition. However, this shift became indistinct at 17 h after oviposition. Prior oviposition on a plant species other than those being compared also affected the preference. These data suggest that learning is involved in the wasp's flight response. Prior oviposition was also observed to have an effect on the antennal searching behavior of the wasp on corn leaves. Such behavioral plasticity may enhance the efficiency by which C. kariyaisearches for polyphagous hosts.     

Response of the soybean aphid parasitoid Binodoxys communis to olfactory cues from target and non-target host-plant complexes

The parasitoid Binodoxys communis (Gahan) (Hymenoptera: Braconidae) is a candidate for release against the Asian soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), in North America. Using a series of Y-tube olfactometer assays, we recorded responses of naïve and experienced B. communis females to odors from both target and non-target host plant complexes. The non-target host plant complexes included three aphid species native to North America [Aphis monardae Oestlund, Aphis oestlundi Gillette, and Aphis asclepiadis (Fitch)] and one species presumed to be exotic to North America (Aphis nerii Boyer de Fonscolombe), all on their respective host plants. We also investigated whether the parasitoid distinguishes between volatiles from soybean infested with A. glycines vs. those of uninfested plants. Volatiles from A. glycines-infested soybean plants and several non-target host plant complexes elicited a response in B. communis, which seemed to be reinforced through oviposition experience. Wasps with experience on a specific host plant complex increased their response to odors of this complex. Neither naïve nor experienced wasps, however, preferred odors from target vs. non-target host plant complexes in choice tests. Our data also indicate that B. communis is unable to distinguish between volatiles from infested vs. uninfested soybean plants. This study shows that B. communis females respond to a broad array of olfactory stimuli, exhibit low fidelity for any particular odor, and employ some behavioral plasticity in their response to volatile cues. We discuss implications of these results for establishment of B. communis and potential undesirable non-target effects associated with the release of this species in North America.     

Variation in flight response of the specialist parasitoidMacrocentrus grandii goidanich to odours from food plants of its European corn borer host

The specialist parasitoidMacrocentrus grandii Goidanich (Hymenoptera: Braconidae) appears to parasitize its polyphagous host, European corn borer (Ostrinia nubilalis (Hübner)) (Lepidoptera: Pyralidae), in only certain habitats. To determine whether it differed in its olfactory response to host-habitat odours, volatiles from four plants were isolated using Tenax. Wind tunnel bioassays of the extracts revealed that, besides corn which was tested in an earlier study, olfactory stimuli for attraction ofM. grandii females were present in potato and snap bean but not in pepper or soybean. To further characterize the response to pepper and soybean, these extracts were bioassayed in combination with an attractive extract. The results indicated that pepper volatiles evoked a neutral response inM. grandii while response to soybean volatiles appeared to be neutral or slightly negative. The innate response to soybean volatiles was altered to one of attraction after oviposition experience on soybean. Seven days after oviposition, experienced females continued to respond positively to soybean volatiles. Components of soybean volatiles responsible for the change in flight behaviour resulting from oviposition experience were eluted by nonpolar and slightly polar solvents. These results support the idea that plant odour may be a factor determining the range of plants on whichM. grandii parasitizes its host. The study indicates the occurrence of associative learning of plant-related volatiles during oviposition inM. grandii, and suggests the involvement of diverse plant compounds in the learning process.     

Influence of adult experience on host microhabitat location by the generalist parasitoid,Campoletis sonorensis (Hymenoptera: Ichneumonidae)

The effect of adult experience on microhabitat location behavior of the generalist parasitoid Campoletis sonorensis (Cameron)was examined in a wind tunnel bioassay. Responses were tested to the odors of two host plants (cotton and sesame) of Heliothis virescens (F.) or a nonhost plant (potato), either damaged and infested with host larvae and host products (host/plant complex) or intact, clean and uninfested. Parasitoid females remained naive or were allowed one oviposition experience on either of the plants, 1 min, 2 h, or 24 h prior their introduction into the wind tunnel. In a no-choice test, parasitoids experienced 1 min prior to bioassay completed significantly more flights to sesame and potato host/plant complexes than did naive parasitoids. However, 24 h after experience, only females experienced on potato completed more flights to the host/ plant complex than did naive females. Parasitoids experienced 1 min prior to flight to undamaged plants showed a slight increase in flight response (significant only for potato) but, after 24 h, completed only as many flights as naive parasitoids. In a dual-choice situation, parasitoids did not show a preference for either of the two host plants but did prefer a host to a nonhost plant. This innate plant preference was not changed by a single oviposition experience. The potential significance of these results to the microhabitat location behavior of C. sonorensisin the field is discussed.     

Effect of Adult Experience on in-Flight Orientation to Plant and Plant–Host Complex Volatiles inAphidius erviHaliday (Hymenoptera, Braconidae)

The effect of adult experience on in-flight orientation to plant–host complex volatiles byAphidius erviHaliday was studied in a wind tunnel bioassay, usingAcyrthosiphon pisum(Harris), maintained on broad bean plants (Vicia faba) as host. A short oviposition experience (15 s) on the plant–host complex (PHC) was sufficient to induce a drastic decrease of flight propensity and stimulated a foraging behavior characterized by intense walking activity. However, flight activity resumed to normal levels 1 h after the oviposition experience on the PHC occurred. For parasitoids conditioned on the PHC for at least 1 min the recorded proportion making oriented flights to the PHC was significantly higher than that for naive females. In contrast, oviposition experience in the absence of plant material did not influence theA. erviflight response. Oviposition attempts on aphid dummies without egg release did not reduce flight activity. WhenA. ervifemales were exposed to glass beads coated withAc. pisumcornicle secretion, a priming effect was observed, resulting, compared with naive females, in a significantly higher rate of oriented flights to the PHC. In contrast, oviposition attempts visually induced by colored aphid dummies did not influence flight behavior. A strong reaction to volatile cues from uninfested plants was induced by oviposition experience on newly infested broad bean plants. This appears to be a case of associative learning. In fact, uninfested broad bean plants are basically unattractive to naiveA. ervifemales. The results demonstrate that adult experience has a considerable influence onA. ervibehavior and may have important implications for biological control of natural pest aphid populations.     

Deterrent effects of intact plants on host-searching behavior of parasitoid wasps

Female parasitoids distinguish between host-infested and intact plants using chemical cues; however, the contribution of intact plants to host searching of parasitoids has not been investigated so far. Here, we tested how host-searching behavior of the parasitoid wasp, Cotesia kariyai (Watanabe) (Hymenoptera: Braconidae), was affected by intact maize plants in a wind tunnel. To determine the best color for material to create a plant model, we observed flight responses of female wasps to paper plant models of four different colors. Wasps tended to land more frequently on green models than other models. Therefore, a green paper model was used for subsequent experiments. In a no-choice test, female wasps showed higher landing rates on a paper plant model treated with herbivore-induced plant volatiles (HIPVs) than on an intact plant. Moreover, in two-choice tests, wasps preferred the plant model with HIPVs over an intact plant with HIPVs. Intact plants seem to deter C. kariyai females. Our findings suggest that information from intact plants also contributes to the host-searching behavior of females in the natural environment.

     

Role of volatiles emitted by host and non-host plants in the foraging behaviour of Dentichasmias busseolae, a pupal parasitoid of the spotted stemborer Chilo partellus

The role of volatiles from stemborer host and non‐host plants in the host‐finding process of Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae) a pupal parasitoid of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) was studied. The non‐host plant, molasses grass (Melinis minutiflora Beauv. (Poaceae)), is reported to produce some volatile compounds known to be attractive to some parasitoid species. The studies were conducted to explore the possibility of intercropping stemborer host plants with molasses grass in order to enhance the foraging activity of D. busseolae in such a diversified agro‐ecosystem. Olfactometric bioassays showed that volatiles from the host plants maize, Zea mays L., and sorghum, Sorghum bicolor (L.) (Poaceae), were attractive to the parasitoid. Infested host plants were the most attractive. Volatiles from molasses grass were repellent to the parasitoid. Further tests showed that volatiles from infested and uninfested host plants alone were preferred over those from infested and uninfested host plants combined with the non‐host plant, molasses grass. In dual choice tests, the parasitoid did not discriminate between volatiles from maize infested by either of the two herbivore species, C. partellus or Busseola fusca Fuller (Lepidoptera: Noctuidae). Volatiles from sorghum infested by C. partellus were preferred over those from C. partellus‐infested maize. The study showed that the pupal parasitoid D. busseolae uses plant volatiles during foraging, with those from the plant–herbivore complex being the most attractive. The fact that volatiles from molasses grass were deterrent to the parasitoid suggested that intercropping maize or sorghum with molasses grass was not likely to enhance the foraging behaviour of D. busseolae. Volatiles from the molasses grass may hinder D. busseolae's host location efficiency.     

Male and female Trybliographa rapae (Hymenoptera: Figitidae) behavioural responses to food plant, infested host plant and combined volatiles

Many parasitoids use volatiles produced by plants as important cues during their food and host search process. We investigated the attraction of the parasitic wasp Trybliographa rapae Westwood (Hymenoptera: Figitidae) to volatiles emitted from plants infested by the cabbage root fly Delia radicum L. (Diptera: Anthomyiidae), as well as to volatiles from a nectar food plant. Behavioural choice tests showed that male parasitoids were not attracted to any volatiles from plants infested by D. radicum or from nectar plants, while females showed clear attraction to both volatile sources. Young females were more attracted to combined volatiles of host and food plants over those from only the host plant, whereas older females showed no differences in attraction to the two odour sources. This suggests that intercropping attractive flowers with host plants could potentially be used to recruit newly emerged parasitoids from surrounding fields while older parasitoids invest more energy in host location than in additional food search. Volatiles from a whole infested plant were chosen over those emitted from separated above- and below-ground parts from infested plants. It is important to consider the availability of both energy and host resources for parasitoids when designing an eco-compatible management of a vegetable crop system.     

Identifying bird cherry-oat aphid Rhopalosiphum padi emigrants, alate exules and gynoparae: application of multivariate methods to morphometric and anatomical features

The host microhabitat location behavior of females of the generalist parasitoid Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae) was studied in a wind tunnel. Visual cues associated with the host plant cotton, Gossypium hirsutum L., were important and significantly more parasitoids completed flights to a damaged 4-leaf cotton plant bearing a Heliothis virescens (F.) (Lepidoptera: Noctuidae) larva and frass than to a similarly damaged single leaf with frass and a larva. This difference in completed flights was not due to differences in amounts of volatiles released by the two stimuli. Both naive and experienced parasitoids responded differently to an undamaged cotton leaf, a mechanially damaged leaf, a naturally damaged leaf with the host removed and a naturally damaged leaf with a host larva. Parasitoids completed significantly fewer flights to the undamaged sources of volatiles than to damaged sources of volatiles. Experienced females responded strongly to all types of damage. The number of flights completed by naive females to the three types of damage differed but not significantly and was less than the number completed by experienced females. Components of the preflight experience were varied to determine which factors were responsible for the higher response of experienced females to the host/plant complex. Oviposition was the most important component of this experience. Contact with host frass or plant damage followed by oviposition did not increase the response over that exhibited by females allowed oviposition only. When frass or damaged plant material were contacted without subsequent oviposition, females completed fewer flights than naive females.     

Host‐searching responses to herbivory‐associated chemical information and patch use depend on mating status of female solitary parasitoid wasps

1. In a tritrophic interaction system consisting of plants, herbivores, and their parasitoids, chemicals released from plants after herbivory are known to play important roles for many female parasitoids to find their hosts efficiently. On the plant side, chemical information associated with herbivory can act as an indirect defence by attracting the natural enemies of the host herbivores. 2. However, mated and virgin females of haplodiploid parasitoids might not necessarily respond to such chemical cues in the same way. Since virgin females can produce only sons, they might refrain from searching for hosts to invest eggs until copulation, in order to produce both sexes. 3. Here, we investigated differential host‐searching behaviours shown by mated and virgin females in the solitary parasitoid wasp, Cotesia vestalis, in response to herbivory‐associated chemical information from cruciferous plants infested by their host larvae, Plutella xylostella. 4. Mated females showed a significantly higher flight preference for host‐infested plants over intact plants, while no preference was observed with virgin females. Mated females also showed more intensive antennal searching and ovipositor probing behaviours to leaf squares with wounds caused by hosts than did virgin females. Furthermore, mated females stayed longer in host patches with higher parasitism rates than virgin females. 5. These results indicate that mating status of C. vestalis females clearly influences their host‐searching behaviour in response to herbivory‐associated chemical information and patch exploitation. Female parasitoids seem to forage for hosts depending on their own physiological condition in a tritrophic system.     

Mate finding in the forest cockchafer, Melolontha hippocastani, mediated by volatiles from plants and females

The response of the forest cockchafer, Melolontha hippocastani F. (Coleoptera, Scarabaeidae), towards volatiles emitted by different host plants and conspecifics was tested in field experiments during the flight period at dusk. Funnel traps containing artificially damaged leaves from the host plants Carpinus betulus L. and Quercus rubra L., as well as from the non‐host plant Prunus serotina Ehrh. caught significantly more beetles than empty control traps. On the other hand, traps baited with undamaged leaves from Q. rubra did not catch significantly more beetles than empty controls. Leaves from C. betulus damaged by beetle feeding did not attract more beetles than artificially damaged leaves. By use of gas chromatography coupled with electroantennographic detection (GC‐EAD) electrophysiological responses of males and females were shown for 18 typical plant volatiles. A synthetic mixture of selected typical green plant volatiles was also highly attractive in the field. A total of 9982 beetles was caught during the field experiments, among them only 33 females. This suggests that attraction to damaged foliage during flight period at dusk is male‐specific. Field experiments testing the attractiveness of female M. hippocastani towards conspecific males by employing caged beetles and beetle extracts indicated that males of M. hippocastani use a female‐derived sex pheromone for mate location. On wired cages containing either unmated feeding females, or unmated females without access to foliage, or feeding males in combination with extracts from unmated females, significantly more males landed during the flight period than on comparable control cages containing feeding males or male extracts. A possible scenario of mate location in M. hippocastani involving feeding‐induced plant volatiles and a female‐derived sex pheromone is discussed.     

Chemically mediated associative learning in the host foraging behavior of the aphid parasitoidAphidius ervi (Hymenoptera: Braconidae)

The effect of experience on the responsiveness of the braconid parasitoidAphidius ervi to host(Acyrthosiphon pisum)-associated cues was investigated on bean plants(Vicia faba) using a wind tunnel bioassay. Oviposition experience on the plant-host complex significantly increased the oriented flight and landing responses ofA. ervi females to an undamaged plant and to a plant-host(A. pisum) complex. However, oviposition experience onA. pisum aphids when isolated from the plant did not change their responses to the intact plant and the complex. Searching on an unwashed plant which had been previously damaged byA. pisum also increased their response to an undamaged plant and a host-damaged plant, whereas the experience of searching on an undamaged plant did not significantly change their responses to undamaged plants. However, when parasitoids were allowed to search on an undamaged plant which had been sprayed withA. pisum honeydew, this significantly increased their response to an undamaged plant. Oviposition experience on the plant-host complex and foraging experience on a host-damaged plant or an undamaged plant sprayed with honeydew also significantly reduced the mean time taken by the parasitoids to respond in the wind tunnel. The behavioral changes associated with such experience were acquired within 30 min and persisted for at least 3 days. The results demonstrate the capacity ofA. ervi to learn associatively olfactory cues from plants, host-damaged plants, and plant-host complexes and confirm the role of aphid honeydew as a host recognition kairomone forA. ervi.     

Role of volatile semiochemicals in host location by the egg parasitoid Anagrus breviphragma

Recent investigations conducted on several tritrophic systems have demonstrated that egg parasitoids, when searching for host eggs, may exploit plant synomones that have been induced as a consequence of host oviposition. In this article we show that, in a system characterized by host eggs embedded in the plant tissue, naïve females of the egg parasitoid Anagrus breviphragma Soyka (Hymenoptera: Mymaridae) responded in a Y‐tube olfactometer to volatiles from leaves of Carex riparia Curtis (Cyperaceae) containing eggs of one of its hosts, Cicadella viridis (L.) (Hemiptera: Cicadellidae). The wasp did not respond to host eggs or to clean leaves from non‐infested plants compared with clean air, whereas it showed a strong preference for the olfactometer arm containing volatiles of leaves with embedded host eggs, compared with the arm containing volatiles of leaves from a non‐infested plant or host eggs extracted from the plant. When the eggs were removed from an infested leaf, the parasitoid preference was observed only if eggs were added aside, suggesting a synergistic effect of a local plant synomone and an egg kairomone. The parasitoid also responded to clean leaves from an egg‐infested plant when compared with leaves from a non‐infested plant, indicating a systemic effect of volatile induction.     

Prey Habitat Location by the Cassava Mealybug Predator Exochomus flaviventris: Olfactory Responses to Odor of Plant, Mealybug, Plant–Mealybug Complex, and Plant–Mealybug–Natural Enemy Complex

Exochomus flaviventris Mader is considered to be the most active predator of the cassava mealybug Phenacoccus manihoti Matile–Ferrero in Central Africa. The response of experienced gravid female coccinellids to the odor of cassava plant (var. Zanaga), unparasitized mealybugs, plant–mealybug complex with or without feeding prey (parasitized or not), and plant–mealybug complex with or without conspecific coccinellids was investigated in a Y-tube olfactometer. The odor of uninfested cassava plants was not more attractive than clean air. Dual-choice tests revealed that mealybug-infested plants were preferred to mealybugs alone and mealybug-damaged plants and were the major sources of volatiles that attract females coccinellids to the microhabitat of its prey. The emission of volatile chemicals did not appear to be limited to the infested parts of the plant but did occur systemically throughout the plant. The presence of conspecific coccinellid larvae or adult males did not modify the attractiveness of the mealybug-infested plants. However, when an infested plant with conspecific predator females (alone or with conspecific males) was compared to an infested plant or infested plant with conspecific males, E. flaviventris females showed a preference for the last two sources of odor. The uninfested plant with conspecific males was also preferred to the uninfested plant with conspecific females. In addition, the odor of conspecific males was preferred over that of conspecific females. Female predators preferred the plant infested with unparasitized mealybugs over the plant infested with mealybugs previously parasitized. These results showed that E. flaviventris females use herbivore-induced plant volatiles during foraging and can detect via olfaction the presence of conspecific gravid females and parasitized prey, thus assessing patch suitability from a distance.     

Adult experience modifies attraction of the leafminer parasitoidOpius dissitus (Hymenoptera: Braconidae) to volatile semiochemicals

Oviposition-experienced females of Opius dissitus Muesebeck, a braconid parasitoid of Liriomyza sativaeBlanchard, preferentially landed on leafminer-infested rather than uninfested lima bean (Phaseolus lunatus L.) plants in a flight tunnel assay. Both naive and oviposition-experiencedparasitoids responded strongly to odors of infested lima bean plants in a four-arm olfactometer in comparison with odors of uninfested plants, suggesting that volatile semiochemicals are used in host location. Parasitoids with an oviposition experience on lima bean (lima-experienced) spent significantly more time in the infested odor than naive individuals, however, eggplant-experienced wasps did not spend significantly more time in the infested odor field than naive wasps. When parasitoids reared on leafminers in lima bean were provided a choice between the odor of infested lima bean and the odor of infested eggplant or cotton, naive and lima-experienced wasps preferred infested lima odor. An oviposition experience on the other plant species resulted in a dramatic shift in preference. It was concluded that the experience effect was due, at least in part, to associative learning, as has been reported for other parasitoids. The parasitoids may perceive unconditioned stimuli during host contact and oviposition on an infested leaf and may associate those stimuli with volatile semiochemicals emanating from the leaf or host. Subsequently, the volatiles associated with the presence of hosts are used in directing the search for hosts.     

Olfactory response of three parasitoid species (Hymenoptera: Braconidae) to volatiles of guavas infested or not with fruit fly larvae (Diptera: Tephritidae)

The olfactory responses of the native parasitoids Doryctobracon areolatus (Szépligeti) and Asobara anastrephae (Muesebeck) and of the exotic parasitoid Diachasmimorpha longicaudata (Ashmead) to guava (Psidium guajava L.) infested or not with fruit fly larvae were evaluated. D. areolatus and D. longicaudata females responded to the odors of uninfested rotting guavas, although D. areolatus was also attracted to fruits at the initial maturation (turning) stage. The females of these species recognized the volatiles of guavas containing Ceratitis capitata (Wied.) larvae. However, in bioassays involving fruits with larvae of different instars, D. longicaudata females were not able to separate between fruits containing C. capitata larvae at the initial instars and larvae at the third instar. In the evaluations of volatiles released by guavas containing C. capitata and Anastrepha fraterculus (Wied.) larvae, the D. longicaudata females were oriented toward the volatiles of fruits containing both host species, but differed significantly from volatiles of guavas containing C. capitata larvae. The D. areolatus females also showed responses to both species, although with a preference for volatiles of fruits containing A. fraterculus larvae. The A. anastrephae females were oriented toward the odors of fruits infested with both fruit fly species. In the shade house, D. longicaudata females were oriented to volatiles of rotting fruits containing larvae or not, but could not significantly differentiate between hosts. D. areolatus females were not attracted toward fruits on the ground in the shade house, regardless of host, suggesting that this parasitoid does not forage on fallen fruits.     

Platypus quercivorus ambrosia beetles use leaf volatiles in host selection

Although chemical volatiles emitted from host and non-host trees have been suggested as important cues for bark and ambrosia beetles, their responses to leaf volatiles is poorly understood. The oak ambrosia beetle, Platypus quercivorus (Murayama) (Coleoptera: Curculionidae), is a vector for the fungus that causes Japanese oak wilt. Using a Y-tube olfactometer, we tested the behavioral response of P. quercivorus to leaf volatiles emitted from four host trees – Quercus crispula Blume, Quercus serrata Murray, Quercus salicina Blume, and Castanea crenata Sieb. & Zucc. (all Fagaceae) – and two non-host trees, Fagus crenata Blume (Fagaceae) and Cryptomeria japonica D. Don (Cupressaceae). A flight mill was used to evaluate the effect of flight on the behavioral response to leaf volatiles. The bioassays were repeated 10× before and 10× after flight in the flight mill for each of the 54 individual beetles. Leaf volatile components were analyzed using gas chromatography–mass spectrometry. The bioassay results supported our hypothesis: P. quercivorus was attracted by the leaf volatiles of hosts and was deterred by the leaf volatiles of non-hosts. The behavioral response of P. quercivorus to the leaf volatiles was stronger after flight. Males had a stronger behavioral response than females to leaf volatiles. The leaf volatile chemical profile of the non-host C. japonica differed from the profile of the host plants. However, the chemical profile of the non-host F. crenata was similar to the profile of the hosts. Our findings provide insight into the functions of leaf chemical volatiles in the interaction of P. quercivorus with its hosts and non-hosts and may help improve the control of P. quercivorus and Japanese oak wilt.     

Choosy egg parasitoids: Specificity of oviposition-induced pine volatiles exploited by an egg parasitoid of pine sawflies

Generalist parasitoids are well‐known to be able to cope with the high genotypic and phenotypic plasticity of plant volatiles by learning odours during their host encounters. In contrast, specialised parasitoids often respond innately to host‐specific cues. Previous studies have shown that females of the specialised egg parasitoid Chrysonotomyia ruforum Krausse (Hymenoptera: Eulophidae) are attracted to volatiles from Pinus sylvestris L. induced by the egg deposition of its host Diprion pini L. (Hymenoptera: Diprionidae), when they have previously experienced pine twigs with host eggs. In this study we investigated by olfactometer bioassays how specifically C. ruforum responded to oviposition‐induced plant volatiles. Furthermore, we studied whether parasitoids show an innate response to oviposition‐induced pine volatiles. Naïve parasitoids were not attracted to oviposition‐induced pine volatiles. The attractiveness of volatiles from pines carrying eggs was shown to be specific for the pine and herbivore species, respectively (species specificity). We also tested whether not only oviposition, but also larval feeding, induces attractive volatiles (developmental stage specificity). The feeding of D. pini larvae did not induce the emission of P. sylvestris volatiles attractive to the egg parasitoid. Our results show that a specialist egg parasitoid does not innately show a positive response to oviposition‐induced plant volatiles, but needs to learn them. Furthermore, the results show that C. ruforum as a specialist does not learn a wide range of volatiles as some generalists do, but instead learns only a very specific oviposition‐induced plant volatile pattern, i.e., a pattern induced by the most preferred host species laying eggs on the most preferred food plant.