Risk of Egg Parasitoid Attraction Depends on Anti-aphrodisiac Titre in the Large Cabbage White Butterfly <Emphasis Type="Italic">Pieris brassicae</Emphasis>

Males of a variety of insects transfer an anti-aphrodisiac pheromone to females during mating that renders them less attractive to conspecific males. In cabbage white butterflies, the transfer of an anti-aphrodisiac can result in the unwanted attraction of tiny egg parasitoid wasps of the genus Trichogramma that hitch-hike with mated female butterflies to a host plant where they parasitize the freshly laid butterfly eggs. Here, we show that the anti-aphrodisiac benzyl cyanide (BC) of the large cabbage white Pieris brassicae is depleted by frequent display of the mate-refusal posture that signals a female’s unreceptivity to mating. This depletion of BC is ecologically important because it results in a reduced risk of attracting the hitch-hiking egg parasitoid Trichogramma brassicae to mated female butterflies over time since mating. Our results indicate for the first time that a reduction in anti-aphrodisiac titre in mated females due to frequent adoption of the mate-refusal posture is beneficial to both mated females and males particularly when parasitoid pressure is high.     

Chemical cues from Murgantia histrionica eliciting host location and recognition in the egg parasitoid Trissolcus brochymenae

Host location and recognition by the egg parasitoid Trissolcus brochymenae were analyzed in terms of response to kairomones from several stages of its host, Murgantia histrionica. In a Y-tube olfactometer, parasitoid females responded by increasing residence time and/or reducing linear speed to chemical cues from gravid females, virgin females and males, fifth and third instars, and eggs. In an open arena, T. brochymenae females also responded to patches contaminated by chemicals from the host in the same stages, sexes, and/or physiological conditions as those tested in the olfactometer. The parasitoid displayed arrestment behavior, increased residence time, changed walking pattern, and intense substrate examination. When host egg clusters or glass dummies with a chemical egg extract were placed on the host-contaminated open arena, these elicited an orientation response in the parasitoid. In addition, the chemical egg extract without dummies elicited the same response, whereas dummies without extract did not influence parasitoid behavior. In a closed arena, the parasitoid females recognized and attempted to probe glass beads treated with chemical extracts of host eggs. There were no significant differences compared with their response to the host eggs, and they did not respond to untreated beads. Host recognition was elicited by chemicals from the follicular secretion used by the host to glue the eggs on the substrate. These results are discussed in relation to the level of the host selection sequence influenced by these cues.     

Chemical Ecology of the host searching behavior in an Egg Parasitoid: are Common Chemical Cues exploited to locate hosts in Taxonomically Distant Plant Species?

Parasitoids are known to exploit volatile cues emitted by plants after herbivore attack to locate their hosts. Feeding and oviposition of a polyphagous herbivore can induce the emission of odor blends that differ among distant plant species, and parasitoids have evolved an incredible ability to discriminate them and locate their hosts relying on olfactive cues. We evaluated the host searching behavior of the egg parasitoid Cosmocomoidea annulicornis (Ogloblin) (Hymenoptera: Mymaridae) in response to odors emitted by two taxonomically distant host plants, citrus and Johnson grass, after infestation by the sharpshooter Tapajosa rubromarginata (Signoret) (Hemiptera: Cicadellidae), vector of Citrus Variegated Chlorosis. Olfactory response of female parasitoids toward plants with no herbivore damage and plants with feeding damage, oviposition damage, and parasitized eggs was tested in a Y-tube olfactometer. In addition, volatiles released by the two host plant species constitutively and under herbivore attack were characterized. Females of C. annulicornis were able to detect and significantly preferred plants with host eggs, irrespectively of plant species. However, wasps were unable to discriminate between plants with healthy eggs and those with eggs previously parasitized by conspecifics. Analysis of plant volatiles induced after sharpshooter attack showed only two common volatiles between the two plant species, indole and β-caryophyllene. Our results suggest that this parasitoid wasp uses common chemical cues released by many different plants after herbivory at long range and, once on the plant, other more specific chemical cues could trigger the final decision to oviposit.

     

Volatile Plant Infochemicals Mediate Plant Preference of Trichogramma chilonis

In India, eggs of the polyphagous noctuid moth Helicoverpa armigera on sorghum are parasitized to high levels by Trichogramma spp., but only rarely are parasitized eggs found on pigeonpea. This study was conducted to test whether volatile plant infochemicals contribute to the different parasitism levels observed on these two crops. In a four-armed airflow olfactometer, volatiles emitted by both sorghum and pigeonpea plants elicited a behavioral response form Trichogramma chilonis females. The parasitoids' response varied depending on the growth stage of the plant. Volatiles emitted by sorghum in the vegetative and reproductive stages arrested the parasitoids. T. chilonis females did not respond to volatiles from pigeonpea in the vegetative stage, but were repelled by volatiles from plants in the reproductive stage. Plants in the reproductive stage are preferred for oviposition by H. armigera. Thus, sorghum is attractive and pigeonpea repellent to T. chilonis females at the time when each plant is attractive to the host. This difference in the parasitoids' response may partly explain the different levels of egg parasitism reported from these two crops. The infochemicals involved in these plant–parasitoid interactions are discussed in the context of the current terminology.     

Herbivore-Induced Plant Volatiles Mediate In-Flight Host Discrimination by Parasitoids

Herbivore feeding induces plants to emit volatiles that are detectable and reliable cues for foraging parasitoids, which allows them to perform oriented host searching. We investigated whether these plant volatiles play a role in avoiding parasitoid competition by discriminating parasitized from unparasitized hosts in flight. In a wind tunnel set-up, we used mechanically damaged plants treated with regurgitant containing elicitors to simulate and standardize herbivore feeding. The solitary parasitoid Cotesia rubecula discriminated among volatile blends from Brussels sprouts plants treated with regurgitant of unparasitized Pieris rapae or P. brassicae caterpillars over blends emitted by plants treated with regurgitant of parasitized caterpillars. The gregarious Cotesia glomerata discriminated between volatiles induced by regurgitant from parasitized and unparasitized caterpillars of its major host species, P. brassicae. Gas chromatography-mass spectrometry analysis of headspace odors revealed that cabbage plants treated with regurgitant of parasitized P. brassicae caterpillars emitted lower amounts of volatiles than plants treated with unparasitized caterpillars. We demonstrate (1) that parasitoids can detect, in flight, whether their hosts contain competitors, and (2) that plants reduce the production of specific herbivore-induced volatiles after a successful recruitment of their bodyguards. As the induced volatiles bear biosynthetic and ecological costs to plants, downregulation of their production has adaptive value. These findings add a new level of intricacy to plant–parasitoid interactions.     

In the Nick of Time: Males of the Parasitoid Wasp <Emphasis Type="Italic">Pimpla disparis</Emphasis> Respond to Semiochemicals from Emerging Mates

Males of the parasitoid wasp Pimpla disparis Viereck (Hymenoptera: Ichneumonidae) aggregate on parasitized gypsy moth, Lymantria dispar, host pupae when the emergence of a prospective mate is imminent or under way. We tested the hypotheses that the developing parasitoid (“DePa”) inside the host pupal case produces a pheromone that attracts and arrests mate-seeking males, and that the pheromone is most effective during the emergence of the parasitoid from the host. Results obtained in two-choice laboratory experiments, with 4–7-d-old virgin males, indicate that (1) DePa-derived semiochemicals arrest males, (2) the opening of a host pupal case strongly arrests males, and (3) the arrestment cue emanates from oral fluid secreted by both female and male parasitoids while they chew their way out of a host pupal case. This phenomenon implies that emerging females, which are haplodiploid and can reproduce without mating, do not engage in active pheromone signaling to attract males, and that mate-seeking males co-opt chemicals involved in eclosion as a mate-finding cue, taking a 50% chance that the prospective mate is a female.     

Evidence for a Host-Marking Pheromone in White Spruce Cone Fly, Strobilomyia neanthracina

Cone flies (Strobilomyia spp.) lay eggs on coniferous cones, and larvae must complete development within the cone on which the eggs are laid. Previous field surveys showed that egg distributions of several species are uniform, suggesting that females avoid ovipositing on cones with conspecific eggs or larvae. In both the field and laboratory, S. neanthracina females walked around cones following oviposition, touching their mouthparts to the cone as they walked. In laboratory bioassays, where females were presented with a cone on which they or another female had oviposited and touched with mouthparts, or one without an egg, females laid preferentially on cones without eggs. However, females laid randomly when presented with a cone on which a female had oviposited but been prevented from touching with her mouthparts following oviposition or another cone without an egg. This indicates that females deposit a host-marking pheromone with their mouthparts following oviposition and that this deters further oviposition on marked hosts. Laboratory and field bioassays indicated that the host-marking pheromone is located in the head and thorax of female flies.     

The Role of Honeydew in Host Searching of Aphid Hyperparasitoids

Foraging in many insect parasitoids is mediated by chemicals associated with hosts. For example, honeydew, the feces of feeding aphids, induces and/or prolongs searching behavior of aphid parasitoids. In the laboratory, we tested if aphid hyperparasitoids, which belong to a higher trophic level, also rely on aphid honeydew to locate their hosts. We used the potato aphid. Macrosiphum euphorbiae, the primary parasitoid, Aphidius nigripes, and four hyperparasitoids, Asaphes suspensus, Dendrocerus carpenteri. Alloxysta victrix, and Syrphophagus aphidivorus that possess different biological attributes and host ranges. We determined if foraging hyperparasitoid females could discriminate between (i) honeydew from a host and a non-aphid host (the potato aphid and the soft brown scale, Coccus hesperidum), and (ii) honeydew from healthy aphids and those parasitized by A. nigripes. Females of A. suspensus did not react to any of the honeydew treatments. While the presence of non-aphid honeydew did not modify the behavior of A. victrix, D. carpenteri, and S. aphidivorus females, they exhibited an increase in searching time and path length but not walking speed when in the presence of honeydew from aphids. However, there were no changes in host searching behaviors, such as antennation or ovipositor probing that have been reported for primary aphid parasitoids. There was no difference in the response of hyperparasitoid females to honeydew from healthy and parasitized aphids. These results indicate that hyperparasitoids may use aphid honeydew, a conspicuous cue from the second trophic level, as an infochemical to locate their hosts.     

Sources of Chemical Signals which Enhance Multiparasitism Preference by a Cleptoparasitoid

The cleptoparasitoid Eupelmus vuilleti recognizes and prefers laying on hosts parasitized by Dinarmus basalis to unparasitized hosts. This recognition is based on the perception of a chemical substance deposited on the surface of the seed. Dufour’s gland secretion and cuticular hydrocarbons of D. basalis are attractive and may mediate the host discrimination. This activity is linked to a mixture of linear and methyl alkanes whose source is apparently the Dufour’s gland.     

Body Odors of Parasitized Caterpillars Give Away the Presence of Parasitoid Larvae to Their Primary Hyperparasitoid Enemies

Foraging success of parasitoids depends on the utilization of reliable information on the presence of their often, inconspicuous hosts. These parasitic wasps use herbivore-induced plant volatiles (HIPVs) that provide reliable cues on host presence. However, host searching of hyperparasitoids, a group of parasitoids that parasitize the larvae and pupae of other parasitoids, is more constrained. Their hosts do not feed on plants, and often are even concealed inside the body of the herbivore host. Hyperparasitoids recently have been found to use HIPVs of plants damaged by herbivore hosts in which the parasitoid larvae develop. However, hyperparasitoids that search for these parasitoid larvae may be confronted with healthy and parasitized caterpillars on the same plant, further complicating their host location. In this study, we addressed whether the primary hyperparasitoid Baryscapus galactopus uses caterpillar body odors to discriminate between unparasitized herbivores and herbivores carrying larvae of parasitoid hosts. We show that the hyperparasitoids made faster first contact and spent a longer mounting time with parasitized caterpillars. Moreover, although the three parasitoid hosts conferred different fitness values for the development of B. galactopus, the hyperparasitoids showed similar behavioral responses to caterpillar hosts carrying different primary parasitoid hosts. In addition, a two-chamber olfactometer assay revealed that volatiles emitted by parasitized caterpillars were more attractive to the hyperparasitoids than those emitted by unparasitized caterpillars. Analysis of volatiles revealed that body odors of parasitized caterpillars differ from unparasitized caterpillars, allowing the hyperparasitoids to detect their parasitoid host.     

Multifunctional communication inRiptortus clavatus (Heteroptera: Alydidae): Conspecific nymphs and egg parasitoidOoencyrtus nezarae use the same adult attractant pheromone as chemical cue

The bean bug,Riptortus clavatus lays scattered eggs (as opposed to the egg masses of pentatomids) on host as well as nonhost plants. Therefore, the first feeding stage (second-instar) nymphs emerging from eggs laid on nonhost plants need a signal that enables them to locate a food source at the lowest energy cost. Male-released (E)-2-hexenyl (E)-2-hexenoate, (E)-2-hexenyl (Z)-3-hexenoate, and myristyl isobutyrate play the double role of attractant pheromone for adults as well as aggregation pheromone, which enables the second-instar nymphs to find the host food plant. These male-specific semiochemicals are released only when foodstuff is available. On the other hand, females ofOoencyrtus nezarae, the most effective parasitoid of the host in Kumamoto, Japan (where the field experiments were conducted), utilize these semiochemicals as kairomones in order to locate the potential host community. Field experiments revealed that the synthetic pheromone rivaled 10 live males in the attraction of adults and second-instar nymphs. Captures of the egg parasitoidO. nezarae females in cylindrical sticky traps were significantly higher in traps baited with the synthetic semiochemicals than in control traps. The number of females captured was significantly higher than the number of males, although the captures in the sticky suction trap system revealed that the populations of male and female were not significantly different.     

Semiochemicals from Fungal Associates of Bark Beetles May Mediate Host Location Behavior of Parasitoids

In laboratory olfactometer bioassays, females of two hymenopteran parasitoid species, Roptrocerus xylophagorum (Ratzeburg) (Hymenoptera: Pteromalidae) and Spathius pallidus (Ashmead) (Hymenoptera: Braconidae), were attracted to odors from bark or bolts of loblolly pine, Pinus taeda L., colonized by bluestain fungi (genus Ophiostoma) associated with the parasitoids' bark beetle hosts. Mock-inoculated bolts and bark were less attractive or unattractive in these bioassays. Bark infested with host larvae that lacked their fungal and other normal microbial associates was attractive to R. xylophagorum females, but was less so than bark infested with larvae possessing their normal complement of associated microbes. In contrast, in oviposition bioassays, R. xylophagorum females spent approximately equal time searching, made similar numbers of oviposition attempts, parasitized similar percentages of hosts, and laid similar numbers of eggs in bark fragments infested with either associate-free or associate-bearing host larvae. Furthermore, in field bioassays using bluestain-inoculated or mock-inoculated loblolly pine bolts as sources of attractants, the numbers of parasitoids attracted by the two treatments did not differ significantly and the two treatments were less attractive than bolts naturally infested with bark beetle larvae. Whereas our laboratory olfactometer data suggest that bark beetle fungal associates may enhance attraction of some parasitoids, our bioassays with associate-free hosts indicate that associate-produced are not required for short-range host location and parasitization. In addition, our field trials indicated that long-range attraction of parasitoids to the host-fungi-tree complex is not caused simply by an interaction between bluestain fungi and tree tissues.     

HOST LOCATION AND HOST DISCRIMINATION BEHAVIOR OF Telenomus isis, AN EGG PARASITOID OF THE AFRICAN CEREAL STEM BORER Sesamia calamistis

In the Republic of Benin, the scelionid egg parasitoid Telenomus isis (Polaszek) is one of the most important control factors of the noctuid maize stem borer Sesamia calamistis. In the present study, the role of various sources of contact kairomones (male or virgin or mated female moths) and of the moth's oviposition substrate (leaf sheath versus filter paper; host plant species) in host location and oviposition behavior of T. isis was investigated in Munger cells, open arenas, and/or Petri dish assays. Furthermore, its ability to distinguish between unparasitized eggs and eggs parasitized by a conspecific female or by the trichogrammatid Lathromeris ovicida was studied. In the Munger cell experiment, T. isis spent more time in moths' odor fields than in the control. There was no difference between virgin and mated females. In the open arena assay, traces left by both the male and female moths acted as contact cues, which elicited an arrestment response in the parasitoid. The residence and patch retention time in the arena with virgin or mated females of S. calamistis was about 4.8 times as long as that with males. The presence of maize leaf sheaths stimulated the oviposition behavior of T. isis when compared to eggs offered on filter paper. During the first 6 hr, more eggs were parasitized on maize leaves, although there was no difference in the final number of offspring between the two substrates. In addition, if eggs of S. calamistis were offered together with different host plant species or alone, maize and sorghum were both more attractive than millet or the egg alone and equally attractive between themselves, indicating that the plant tissue influences host finding of T. isis. Both T. isis and L. ovicida recognized markings of conspecific females, and intraspecific superparasitism was therefore low. Interspecific superparasitism was more than three times higher for L. ovicida than for T. isis, indicating that only T. isis was able to recognize the marking of the other species and tried to avoid superparasitism. Emergence of parasitoids from multiparasitized eggs generally was in favor of L. ovicida regardless of species order.     

Host-recognizing kairomones for parasitic wasp,Anisopteromalus calandrae,from larvae of azuki bean weevil,Callosobruchus chinensis

Host-recognizing kairomones for the stinging behavior of the parasitic wasp, Anisopteromalus calandrae, were identified on host azuki bean weevil larvae, Callosobruchus chinensis (L.). The kairomones were extracted with acetone from Chinese green beans, from which emerged wasps and host weevils had been removed. The kairomones are a mixture of triacylglycerols and fatty acids, each of which is separately active, and with no observable synergistic effect between them. These compounds are known to be constituents of an oviposition-marking pheromone of host azuki bean weevils. However, they differ from the previously reported saturated hydrocarbons and diacylglycerols of the kairomone that another parasitic wasp, Dinarmus basalis, uses for the host recognition of C. chinensis. Thus, A. calandrae and D. basalis selectively utilize different constituents of the oviposition-marking pheromone of C. chinensis as host-recognizing kairomones.     

Chemically mediated associative learning: An important function in the foraging behavior ofMicroplitis croceipes (Cresson)

When experienced by contact with feces from hosts feeding on cowpeas, laboratory-reared females ofMicroplitis croceipes, a larval parasitoid ofHeliothis spp., orient and fly to odors of the same feces, whereas naive laboratory-reared females do not. Flight-tunnel studies revealed that associative learning occurs during female encounters with hosts and host products. When females antennate host feces, they learn to recognize the volatile odors associated with the feces. Females even can be conditioned to respond to novel and otherwise unattractive odors such as vanilla extract by exposure to these volatile substances in association with a water extract of the feces. They apparently link the volatile odors with a nonvolatile hostspecific recognition chemical found in the feces. The antennating stimulant, 13-methylhentriacontane, was found to be a valuable ingredient, apparently as a facilitator of the initial antennation and subsequent linkage of the volatiles to the nonvolatile host recognition cue.     

Aggregated oviposition inDelia antiqua (Meigen): A case for mediation by semiochemicals

Experiments conducted in the laboratory tested the hypotheses that aggregated oviposition by onion maggot flies,Delia antiqua (Meigen), is caused by stimuli associated with ovipositing females, newly laid eggs, or both. Using a paired oviposition station bioassay that eliminated visual stimuli associated with the treatment under study, 67% of the eggs laid by caged females were in response to the odor of females already ovipositing on an onion slice, as opposed to 33% of the eggs laid in response to an onion slice alone. When newly laid eggs were transferred to onion slices and held for either 24 or 48 hr before being bioassayed against similarly aged untreated onions, 74% and 97% of the eggs were laid at the egg-treated onion stations, respectively. Similar results were achieved when an aqueous wash of newly laid eggs was applied to the onion slice. When the egg wash was processed through a bacterial filter or when eggs were present but not in contact with onions, all response was eliminated. These results implicate microorganisms transmitted on the egg surface in creating an attraction for ovipositing females. Heptane extracts of ovipositor tips from mated, ovipositing females induced 72% of the test females to oviposit near points at which extracts were applied to the oviposition station floor. A behavioral sequence for an optimal host-selection strategy is hypothesized, whereby host-seeking female onion flies respond to host-derived alkyl sulfides at long range and metabolic by-products of microbially infested hosts and visual cues at short range (ca. l m), with final selection of oviposition sites potentially reinforced by contact with an aggregation pheromone released or left on the substrate by ovipositing females.     

The Egg Parasitoid <Emphasis Type="Italic">Trissolcus basalis</Emphasis> uses <Emphasis Type="Italic">n</Emphasis>-nonadecane,a Cuticular Hydrocarbon from its Stink Bug Host <Emphasis Type="Italic">Nezara viridula</Emphasis>, to Discriminate Between Female and Male Hosts

Contact kairomones from adult southern green stink bugs, Nezara viridula (L.) (Heteroptera: Pentatomidae) that elicit foraging behavior of the egg parasitoid Trissolcus basalis (Wollaston) were investigated in laboratory experiments. Chemical residues from tarsi and scutella of N. viridula induced foraging by gravid female T. basalis. Residues from body parts of female N. viridula elicited stronger responses than those from the corresponding body parts of males. Deproteinized tarsi still elicited searching responses from wasps, indicating that the kairomone was not proteinaceous. Hexane extracts of host cuticular lipids induced searching responses from T. basalis, with a strong preference for extracts from female hosts. Extracts consisted primarily of linear alkanes from nC₁₉ to nC₃₄, with quantitative and qualitative differences between the sexes. Extracts of female N. viridula contained more nC₂₃, nC₂₄, and nC₂₅ than the corresponding extracts from males, whereas nC₁₉ was detected only in extracts from males. Direct-contact solid phase microextraction (DC-SPME) of N. viridula cuticle and of residues left by adult bugs walking on a glass plate confirmed gender-specific differences in nC₁₉. Trissolcus basalis females responded weakly to a reconstructed blend of the straight-chain hydrocarbons, suggesting that minor components other than linear alkanes must be part of the kairomone. Addition of nC₁₉ to hexane extracts of female N. viridula significantly reduced the wasps’ arrestment responses, similar to wasps’ responses to hexane extracts of male hosts. Overall, our results suggest that a contact kairomone that elicits foraging by T. basalis females is present in the cuticular lipids of N. viridula, and that the presence or absence of nC₁₉ allows T. basalis females to distinguish between residues left by male or female hosts. The ecological significance of these results in the host location behavior of scelionid egg parasitoids is discussed.     

Population-Related Variation in Plant Defense more Strongly Affects Survival of an Herbivore than Its Solitary Parasitoid Wasp

The performance of natural enemies, such as parasitoid wasps, is affected by differences in the quality of the host’s diet, frequently mediated by species or population-related differences in plant allelochemistry. Here, we compared survival, development time, and body mass in a generalist herbivore, the cabbage moth, Mamestra brassicae, and its solitary endoparasitoid, Microplitis mediator, when reared on two cultivated (CYR and STH) and three wild (KIM, OH, and WIN) populations of cabbage, Brassica oleracea. Plants either were undamaged or induced by feeding of larvae of the cabbage butterfly, Pieris rapae. Development and biomass of M. brassicae and Mi. mediator were similar on both cultivated and one wild cabbage population (KIM), intermediate on the OH population, and significantly lower on the WIN population. Moreover, development was prolonged and biomass was reduced on herbivore-induced plants. However, only the survival of parasitized hosts (and not that of healthy larvae) was affected by induction. Analysis of glucosinolates in leaves of the cabbages revealed higher levels in the wild populations than cultivars, with the highest concentrations in WIN plants. Multivariate statistics revealed a negative correlation between insect performance and total levels of glucosinolates (GS) and levels of 3-butenyl GS. However, GS chemistry could not explain the reduced performance on induced plants since only indole GS concentrations increased in response to herbivory, which did not affect insect performance based on multivariate statistics. This result suggests that, in addition to aliphatic GS, other non-GS chemicals are responsible for the decline in insect performance, and that these chemicals affect the parasitoid more strongly than the host. Remarkably, when developing on WIN plants, the survival of Mi. mediator to adult eclosion was much higher than in its host, M. brassicae. This may be due to the fact that hosts parasitized by Mi. mediator pass through fewer instars, and host growth is arrested when they are only a fraction of the size of healthy caterpillars. Certain aspects of the biology and life-history of the host and parasitoid may determine their response to chemical challenges imposed by the food plant.     

Host Sex Discrimination by an Egg Parasitoid on Brassica Leaves

Egg parasitoids are able to find their hosts by exploiting their chemical footprints as host location cues. In nature, the apolar epicuticular wax layer of plants that consists of several classes of hydrocarbons serves as the substrate that retains these contact kairomones. However, experiments on chemical footprints generally have used filter paper as substrate to study insect behavior. Here, we explored the ability of Trissolcus basalis (Scelionidae) females to discriminate between footprint cues left by male and female Nezara viridula (Pentatomidae) on leaves of their host plant Brassica oleracea (broccoli). Furthermore, we analyzed the chemical composition of the outermost wax layer of broccoli leaves to evaluate the degree of overlap in insect and plant cuticular hydrocarbons that could lead to masking effects in the detection of footprint cues. Our results showed that B. oleracea epicuticular wax retains the chemical footprints of adult bugs and allows T. basalis females to differentiate hosts of different sex. Traces of female bugs elicited more extensive searching behavior in egg parasitoids than traces of males. The application of n-nonadecane, a compound specific to male N. viridula, on the tarsi of female bugs prevented parasitoid females from distinguishing between host male and host female footprints. Analyses of B. oleracea leaves revealed that epicuticular waxes were mainly composed of linear alkanes, ketones, and secondary alcohols. Alkanes were dominated by n-nonacosane (nC29) and n-hentriacontane (nC31), while male-specific n-nonadecane (nC19) was absent. The ecological significance of these results for parasitoid host location behavior is discussed.     

Kairomones Extracted from Rice Yellow Stem Borer and their Influence on Egg Parasitization by <Emphasis Type="Italic">Trichogramma japonicum</Emphasis> Ashmead

Host location and acceptance by egg parasitoids can be mediated by close-range host stimuli. In this study, we tested the response of Trichogramma japonicum Ashmead to cuticular extracts of adult and larval rice yellow stem borer (YSB), Scripophaga incertulas Walker. We also studied the wasps’ response to extracts from YSB larval frass. Laboratory bioassays revealed that hexane extracts of the adult host body stimulate ovipositor probing of T. japonicum. Extracts of larval frass also stimulated parasitization. In contrast, host larval cuticular extracts had no effect on parasitization rates. Fractionation of the crude extracts of adult YSB cuticular extracts was performed using silica gel chromatography, followed by bioassays of the individual fractions to test their effects on wasp behavior. Analyses of the most active fractions by gas chromatography–mass spectrometry revealed that the extract contained saturated long chain alkanes and alkenes, with carbon numbers ranging from C₂₀ to C₃₂. Hydrocarbons were applied onto host eggs to test their effects on parasitization rates. Treatments of eggs with docosane, tetracosane, pentacosane, and eicosane enhanced host egg parasitization, while pentadecane, hexadecane, and nonadecane deterred oviposition. An erratum to this article can be found at