Induced volatiles in soybean and pigeon pea plants artificially infested with the neotropical brown stink bug, Euschistus heros, and their effect on the egg parasitoid, Telenomus podisi

Herbivory is known to increase the emission of volatiles, which attract natural enemies to herbivore‐damaged plants in laboratory and agricultural systems. We report on signalling through volatiles induced by Euschistus heros (F.) (Heteroptera: Pentatomidae) in two legumes that influence the attraction and retention of the egg parasitoid Telenomus podisi (Ashmead) (Hymenoptera: Scelionidae). Air‐borne extracts obtained from two host plants of E. heros, soybean, Glycine max, and pigeon pea, Cajanus cajan (Leguminosae), produce a different blend of emitted volatiles when attacked by adult males or females and nymphs of the pest species, compared with the undamaged plants. The same results were obtained when the plants were treated with extracted saliva of E. heros which had been mechanically introduced into the plants. This indicates that some substance in the saliva contributed to the release of the volatiles. Bioassays in a Y‐tube olfactometer with female T. podisi and treated plants confirmed the significant preference of the egg parasitoid for plants attacked by either males, females, or fourth instar nymphs of the pest species. On the other hand, volatile extracts obtained from soybean subjected to the velvetbean caterpillar, Anticarsia gemmatalis, a non‐host species for T. podisi, showed a different blend of volatiles compared to those obtained from plants subjected to E. heros. Additionally, the volatiles obtained from this plant–host complex were not attractive to T. podisi. These results indicate that E. heros causes an increase in the emission of specific plant volatiles, and that the induction is possibly caused by an elicitor present in the pest saliva. The possibility that these plant volatiles play an important role in the attraction and retention of the egg parasitoid T. podisi is discussed.     

Attraction of <Emphasis Type="Italic">Telenomus podisi</Emphasis> to volatiles induced by <Emphasis Type="Italic">Euschistus heros</Emphasis> in three different plant species

Specialized natural enemies that forage for polyphagous hosts need to locate hosts on different plants. Telenomus podisi (Hymenoptera: Platygastridae) is a stink bug egg parasitoid with a preference for Euschistus heros (Hemiptera, Pentatomidae), a polyphagous species. The aim of this study was to evaluate the induction of defences in three E. heros host plants: maize (Zea mays), sunflower (Helianthus annuus) and pigeon pea (Cajanus cajan). We hypothesized that E. heros damage to these three plants enhances the attraction of the parasitoid T. podisi as has been observed in other systems. Using Y-tube olfactometer bioassays, we tested parasitoid responses to combinations of the following odour sources: clean air, undamaged plants and plants damaged by stink bug feeding. Volatiles were collected by means of dynamic headspace collection and analysed by gas chromatography coupled to mass spectrometry. T. podisi did not distinguish odours from undamaged plants against air for any of the three plant species. For maize, the parasitoid preferred the odour from herbivore-damaged plants over both clean air and undamaged plants. For sunflower, the parasitoid only preferred the odour of herbivore-damaged plants over the odour of undamaged plants. For pigeon pea, no preferences were observed. Quantitative differences in the volatile profile of damaged and undamaged plants were observed in each plant species. We conclude that sunflower and maize plants, when damaged by E. heros, release volatiles that attract the parasitoid T. podisi; the parasitoid appears to use a different blend composition to distinguish herbivore-damaged plants of each species.     

Influence of volatile compounds from herbivore‐damaged soybean plants on searching behavior of the egg parasitoid Telenomus podisi

Parasitoids use herbivore‐induced plant volatiles (HIPVs) to locate their hosts. However, there are few studies in soybean showing the mechanisms involved in the attraction of natural enemies to their hosts and prey. The objective of this study was to evaluate the influence of volatile organic compounds (VOCs) of soybean, Glycine max (L.) Merr. (Fabaceae) (cv. Dowling), that were induced after injury caused by Euschistus heros (Fabricius) (Hemiptera: Pentatomidae), on the searching behavior of the egg parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae). Four HIPVs from soybean, (E,E)‐α‐farnesene, methyl salicylate, (Z)‐3‐hexenyl acetate, and (E)‐2‐octen‐1‐ol, were selected, prepared from standards at various concentrations (10^?6 to 10^?1 m ), and tested individually and in combinations using a two‐choice olfactometer (type Y). Telenomus podisi displayed a preference only for (E,E)‐α‐farnesene at 10^?5 m when tested individually and compared to hexane, but they did not respond to the other compounds tested individually at any concentration or when combinations of these compounds were tested. However, the parasitoids stayed longer in the olfactometer arm with the mixture of (E,E)‐α‐farnesene + methyl salicylate at 10^?5 m than in the arm containing hexane. The results suggest that (E,E)‐α‐farnesene and methyl salicylate might help T. podisi to determine the presence of stink bugs on a plant. In addition, bioassays were conducted to compare (E,E)‐α‐farnesene vs. the volatiles emitted by undamaged and E. heros‐damaged plants, to evaluate whether (E,E)‐α‐farnesene was the main cue used by T. podisi or whether other minor compounds from the plants and/or the background might also be used to locate its host. The results suggest that minor volatile compounds from soybean plants or from its surroundings are involved in the host‐searching behavior of T. podisi.     

Semiochemical and physical stimuli involved in host recognition by Telenomus podisi (Hymenoptera: Scelionidae) toward Euschistus heros (Heteroptera: Pentatomidae)

The egg parasitoid, Telenomus podisi, was shown to recognize its host, Euschistus heros, through both chemical and physical cues. These were determined in short-range bioassays. The cues comprised fertile and infertile host eggs, egg extracts, crude extracts of adult males and females and successive dilutions of the synthetic racemic mixture of methyl 2,6,10-trimethyltridecanoate, a male-produced pheromone of E. heros. Some of the treatments used induced a selection process in T. podisi, through host recognition behaviour, indicating a consistent response of this species to E. heros. The possibility that some of these compounds could be exploited as long-range kairomones, by T. podisi, is discussed. Using GC analysis, an unidentified compound (Rt 24.8 min), possibly from the egg adhesive material, was detected from E. heros egg extracts. Its retention time compared to the methyl 2,6,10-trimethyltridecanoate showed a lower volatility, suggesting that the egg adhesive may act as a short-range kairomone. Physical cues appeared to be an important component in the host selection process by T. podisi. The parasitoid discriminated infertile eggs which are differently shaped and smaller than fertile eggs.     

cis-Jasmone indirect action on egg parasitoids (Hymenoptera: Scelionidae) and its application in biological control of soybean stink bugs (Hemiptera: Pentatomidae)

In many plants, the secondary metabolite cis-jasmone activates the metabolic pathway that produces volatile organic compounds attractive to natural enemies and, sometimes, repellent to herbivores. Previous studies indicate that the feeding damage caused by the herbivore Euschistus heros or the exogenous application of cis-jasmone in soybean plants induces the release of herbivore-induced plant volatiles (HIPVs) with a similar chemical profile and these compounds can attract the stink bug egg parasitoid Telenomus podisi (Scelionidae). Herein we tested in field conditions the effect of exogenous application of cis-jasmone in soybean plants on the parasitoid and stink bug community and on stink bug egg parasitism. In two areas, one within a soybean and another within a Crotalaria matrix, we randomly distributed 2 m² plots, with soybean plants induced (treatment, n = 5) or not induced by cis-jasmone (control, n = 5) in the field. We sampled the parasitoid community weekly with yellow sticky traps (n = 3/plot) and monitored parasitism with sentinel eggs of E. heros (n = 150/plot). We also monitored the population of stink bugs weekly, by sampling each plot with shake-cloth technique. The abundance of Scelionidae was highest overall and also in treated plots during the first four weeks in the area with a soybean matrix, but decreased thereafter. The richness of parasitoid families was similar between treatment and control plots in the area with a soybean matrix, but higher in control plots in the area with a Crotalaria matrix. Evenness was higher in control plots in the area with soybean matrix, whereas the reverse occurred in the area with a Crotalaria matrix. Results suggest that treatment with cis-jasmone effectively attracted and enhanced the population of scelionid parasitoids, but had no effect on the occurrence and intensity of parasitism and in the number of stink bugs.     

Plant population size and isolation affect herbivory of <Emphasis Type="Italic">Silene latifolia</Emphasis> by the specialist herbivore <Emphasis Type="Italic">Hadena bicruris</Emphasis> and parasitism of the herbivore by parasitoids

Habitat fragmentation can affect levels of herbivory in plant populations if plants and herbivores are differentially affected by fragmentation. Moreover, if herbivores are top–down controlled by predators or parasitoids, herbivory may also be affected by differential effects of fragmentation on herbivores and their natural enemies. We used natural Silene latifolia populations to examine the effects of plant population size and isolation on the level of herbivory by the seed predating noctuid Hadena bicruris and the rate of parasitism of the herbivore by its parasitoids. In addition, we examined oviposition rate, herbivory and parasitism in differently sized experimental populations. In natural populations, the level of herbivory increased and the rate of parasitism decreased with decreasing plant population size and increasing degree of isolation. The number of parasitoid species also declined with decreasing plant population size. In the experimental populations, the level of herbivory was also higher in smaller populations, in accordance with higher oviposition rates, but was not accompanied by lower rates of parasitism. Similarly, oviposition rate and herbivory, but not parasitism rate, increased near the edges of populations. These results suggests that in this system with the well dispersing herbivore H. bicruris, habitat fragmentation increases herbivory of the plant through a behavioural response of the moth that leads to higher oviposition rates in fragmented populations with a reduced population size, increased isolation and higher edge-to-interior ratio. Although the rate of parasitism and the number of parasitoid species declined with decreasing population size in the natural populations, we argue that in this system it is unlikely that this decline made a major contribution to increased herbivory.     

Effect of resistant and susceptible soybean cultivars on the attraction of egg parasitoids under field conditions

The association of resistant crop varieties and biological pest control has great potential for pest management, as resistant cultivars may affect herbivore population dynamics by interfering with their biology and search behaviour for host plants. In addition, resistant varieties can also affect the efficiency of natural enemies. The aims of this work were to evaluate the influence of the soybean cultivars Dowling (resistant), IAC 100 (resistant) and Silvânia (susceptible) under field conditions on: (i) the abundance of parasitoids in the Platygastridae family and the stink bug Euschistus heros and (ii) the parasitism of stink bug eggs by these natural enemies. There was no difference between cultivars in stink bug distribution in the field. The parasitoids Telenomus podisi, Trissolcus teretis, Tr. urichi and Tr. brochymenae emerged from the sentinel eggs of E. heros, and T. podisi was the most abundant species observed during the reproductive stage R6. The cultivars Dowling and IAC 100 attracted a higher number of Platygastridae parasitoids, T. podisi and Tr. teretis, and the abundance of these parasitoids during the period from R1 to R7 might have being sufficient to control the stink bug population. These results suggest that the cultivars Dowling and IAC 100 have important attributes that should be taken into account in the implementation and development of new cultivars in breeding programmes that aim to obtain plants more resistant to stink bugs and more attractive to natural enemies.     

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.     

Storage of Euschistus heros Eggs (Fabricius) (Hemiptera: Pentatomidae) in Liquid Nitrogen for Parasitization by Telenomus podisi Ashmead (Hymenoptera: Platygastridae)

Records in the literature with regard to the influence of freezing of pentatomid eggs on parasitism by microhymenopterans are scarce. In this research, we compared the storage of Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) eggs in liquid nitrogen for different periods with the objective of optimizing the multiplication of Telenomus podisi Ashmead (Hymenoptera: Platygastridae) in the laboratory. Fresh eggs of E. heros were exposed (S3, S6) or not (NS3, NS6) to UV light for 30 min and stored in 1.5-mL plastic vials in liquid nitrogen either for 3 (S3, NS3) or 6 months (S6, NS6), and egg suitability to parasitoid development was compared to control eggs exposed (SC) or not (NSC) to UV treatment. Global data analysis showed that E. heros eggs stored in liquid nitrogen with or without UV treatment, for 3 or 6 months, were suitable for T. podisi parasitization.     

Selective responses of Trissolcus basalis and Telenomus podisi to chemical footprints of preferred hosts

Chemical trails of the hosts (footprints) are important cues for the host searching behaviour of egg parasitoids of the family Scelionidae. The present study aims to determine the influence of the footprints of three neotropical stink bugs (Euchistus heros, Dichelops melacanthus and Nezara viridula) on the foraging behaviour of two parasitoids, Trissolcus basalis and Telenomus podisi, as well as a possible selective response to fooprints of their preferred hosts. Accordingly, Tr. basalis and Te. podisi females are allowed to forage on open arenas where E. heros, D. melacanthus or N. viridula had walked or on open arenas that had been treated with samples of an extract from each stink bug's footprints. Hexane extracts of stink bug footprints are obtained from solvent-washed Petri dishes where insects were allowed to walk for 24 h, and these extracts were analyzed by gas chromatography-flame ionization detection and gas chromatography-mass spectrometry. Each parasitoid responds selectively to the footprints of their preferred host (Tr. basalis to footprints of N. viridula and Te. podisi to footprints of E. heros). Twenty-six compounds comprising of C18 to C35 (saturated and unsaturated) and methyl branched hydrocarbons were identified in extracts of E. heros, D. melacanthus and N. viridula, respectively. There are significant differences in the total amount of the compounds identified in the footprint stink bug's extracts and also a difference in the amounts of individual compounds. In addition, the behavioural assays showed that footprints of stink bugs are stimuli that are used by egg parasitoids to search, discriminate and selectively locate their preferred host.     

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.     

Influence of visual cues on host‐searching and learning behaviour of the egg parasitoids Telenomus podisi and Trissolcus basalis

Insect parasitoids use a variety of chemical and physical cues when foraging for hosts and food. Parasitoids can learn cues that lead them to the hosts, thus contributing to better foraging. One of the cues that influence host‐searching behaviour could be colour. In this study, we investigated the ability of females of the parasitoid wasps Telenomus podisi Ashmead and Trissolcus basalis Wollaston (both Hymenoptera: Scelionidae) to respond to colours and to associate the presence of hosts – eggs of Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) – with coloured substrates after training (associative learning). Two sets of experiments were conducted: in one the innate preference for substrate colours was examined, in the other associative learning of substrate colour and host presence was tested in multiple‐choice and dual‐choice experiments. In the associative learning experiments, Te. podisi and Tr. basalis were trained to respond to differently coloured substrates containing hosts in two sessions of 2 h each, with 1‐h intervals. In multiple‐choice experiments, the wasps displayed innate preference for yellow substrates over green, brown, black, or white ones. Even after being trained on substrates of different colours, both parasitoids continued to show preference for yellow substrates. The response to the colours of substrates of both parasitoids was related with the orientation to the plant foliage during the search for hosts.     

Field evaluation of (E)-2-hexenal efficacy for behavioral manipulation of egg parasitoids in soybean

We studied the influence of synthetic (E)-2-hexenal on the abundance of Telenominae aiming to attract parasitoids and enhance stink bug egg parasitism in treated areas. We conducted experiments in 2006, 2007 and 2008 soybean seasons with two short-term (one week) and one long-term (seven weeks) experiment, respectively. We evaluated the abundance of parasitoids with yellow sticky traps and estimated the incidence and intensity of parasitism with sentinel eggs of Euschistus heros Fabricius (Hemiptera: Pentatomidae) or with tulle bags, enclosing laboratory pregnant E. heros as an egg source. In short-term experiments, there was increased abundance of Trissolcus spp. (Hymenoptera: Platygastridae: Telenominae) in treated areas, associated with greater intensity of parasitism. In long-term experiments, treatment with (E)-2-hexenal did not influence the abundance of Telenominae or parasitism levels, but increased egg predation. Applications of (E)-2-hexenal can be used to increase recruitment of Trissolcus spp. in the early flowering stages of soybean and also to attract other natural enemies, but do not increase egg parasitism.     

Oviposition by a moth suppresses constitutive and herbivore-induced plant volatiles in maize

Plant volatiles function as important signals for herbivores, parasitoids, predators, and neighboring plants. Herbivore attack can dramatically increase plant volatile emissions in many species. However, plants do not only react to herbivore-inflicted damage, but also already start adjusting their metabolism upon egg deposition by insects. Several studies have found evidence that egg deposition itself can induce the release of volatiles, but little is known about the effects of oviposition on the volatiles released in response to subsequent herbivory. To study this we measured the effect of oviposition by Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) moths on constitutive and herbivore-induced volatiles in maize (Zea mays L.). Results demonstrate that egg deposition reduces the constitutive emission of volatiles and suppresses the typical burst of inducible volatiles following mechanical damage and application of caterpillar regurgitant, a treatment that mimics herbivory. We discuss the possible mechanisms responsible for reducing the plant’s signaling capacity triggered by S. frugiperda oviposition and how suppression of volatile organic compounds can influence the interaction between the plant, the herbivore, and other organisms in its environment. Future studies should consider oviposition as a potential modulator of plant responses to insect herbivores.     

Differential induction of volatiles in rice plants by two stink bug species influence behaviour of conspecifics and their natural enemy Telenomus podisi

Tritrophic interactions mediated by semiochemicals have been intensively studied from the viewpoint of ecological relationships with Nearctic tritrophic organisms. However, there are few studies involving interactions with different herbivores on the same host plant in Neotropical systems. The objective of the current study was to investigate the effects of herbivory by two species of stink bugs (Heteroptera: Pentatomidae) with the same feeding habit – Tibraca limbativentris Stål and Glyphepomis spinosa Campos & Grazia – on indirect and direct defence strategies of rice plants. The responses of each stink bug species (virgin and mated females) and of their main natural enemy, the egg parasitoid Telenomus podisi Ashmead (Hymenoptera: Platygastridae; mated females), to volatiles from undamaged and herbivore-damaged rice plants were evaluated using a Y-tube olfactometer. The results showed that rice plants responded differently to T. limbativentris or G. spinosa herbivory, enhancing the production of a different blend of volatile compounds, which reduced the attraction for conspecific stink bugs and elicited the foraging behaviour of T. podisi.     

Increasing host age does not have the expected negative effects on the fitness parameters of an egg parasitoid

Host age is an important determinant of host acceptance and suitability for egg parasitoids. As host embryonic development advances, the quality of resources available to the parasitoid offspring typically declines, usually resulting in reduced acceptance levels by foraging females and lower offspring fitness. We examined the ability of the parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae) to parasitize and develop in Podisus maculiventris (Say) (Hemiptera: Pentatomidae) eggs of different ages. In laboratory experiments, we measured the effect of host age (6, 24, 48, 72, 96, or 120 h old) on parasitism rate and offspring fitness parameters such as survival, development time, sex ratio, and size. Contrary to our expectations, parasitism rate did not differ between host age treatments, nor did sex ratio allocation, offspring size, or the fecundity of newly emerged female offspring. However, parasitoid offspring had a longer development time with increasing host age. This trend was stronger for males than for females, which we suggest could reduce the degree of protandry among offspring emerging from older host eggs, thus increasing the rate of virginity upon leaving the emergence patch and resulting in more frequent off‐patch mating by female offspring in nature. Overall, our results suggest that all stages of P. maculiventris embryonic development are suitable for acceptance and development of T. podisi. Unlike most species of egg parasitoids, T. podisi has evolved mechanisms to utilize host resources, regardless of host developmental stage, with relatively minor fitness consequences.     

Abundances of five parasitoids attacking the scale insect <Emphasis Type="Italic">Nipponaclerda biwakoensis</Emphasis> on morphologically changed reed shoots due to damage by a stem-boring caterpillar

Abundances of the scale insect Nipponaclerda biwakoensis and its five parasitoids per shoot of the common reed, Phragmites australis, were compared between shoots damaged by a stem-boring caterpillar and undamaged shoots. Reed shoots that were damaged by the stem-borer in spring change morphologically during summer, inducing tillers from the nodes beneath the damaged part. The number of female scales per shoot did not differ significantly between damaged and undamaged shoots in the second scale generation (September), but was significantly lower on damaged shoots in the third generation (November). Three parasitoid species attacking the scale exhibited different responses to the shoot damage, with the response by each parasitoid being constant in the two scale generations: the parasitism rate by Aprostocetus sp. per shoot was higher on damaged shoots, whereas that by Astymachus japonicus was lower on damaged shoots, and no difference was detected for Boucekiella depressa. In the third scale generation, the parasitism rate by Encyrtidae sp. 1 showed no difference, with respect to shoot damage, whereas that by Encyrtidae sp. 2 was lower on damaged shoots. In three dominant parasitoids, shoot damage had no effect on the number of emerging adults per host, and the sex ratio and body size of the adults. The number of emerging adults per shoot differed significantly between damaged and undamaged shoots for four parasitoids, except B. depressa. These results suggest that shoot damage by the stem-borer exerts a delayed negative impact on the scale numbers and affects the parasitism rate of the scales by three parasitoids and the emerging adult numbers of four parasitoids.     

Is It Possible to Manipulate Scelionidae Wasps’ Preference to a Target Host?

Parasitoid host selection is mainly mediated by chemical cues, which can be adjusted by experience, changing their innate behavior. Therefore, this study evaluated if immature experience (pre-imaginal conditioning) on eggs and volatiles from different host eggs has influence on parasitism and chemotaxic behavior of Telenomus podisi Ashmead and/or Trissolcus basalis Wollaston (Hymenoptera: Scelionidae). Both wasp species were submitted to a multiple-choice parasitism test among Euschistus heros (Fabricius), Piezodorus guildinii (Westwood), and Nezara viridula L. (Hemiptera: Pentatomidae) (Hemiptera: Pentatomidae) egg masses. Eggs from these three stink bugs were equally offered to female parasitoids. After that, adults which emerged from each host were also exposed to parasitism in a multiple-choice test for up to an additional generation. Moreover, in olfactometer “Y,” the behavior of innate and experienced T. podisi females to volatiles from hosts’ egg extracts was tested, to study their learning and memory ability. The original host had influence on T. podisi parasitism; however, T. basalis always parasitized more N. viridula eggs independently of its last rearing host. Innate T. podisi females responded positively to E. heros and P. guildinii egg volatiles, but this behavior was not observed in N. viridula. When T. podisi females were experienced on egg volatiles from a new host, they showed significant learning and memory ability for the specific host volatile for, at least, 24 h. Experienced wasps responded positively to N. viridula and through this result we have evidences about the possibility to manipulate wasp’s preferences to a specific target host.     

The role of host plant species in the phenotypic differentiation of sympatric populations of Aleiodes nolophanae and Cotesia marginiventris

The ecology of parasitoids is strongly influenced by their host plant species. Parasitoid fitness can be affected by a variety of plant traits that could promote phenotypic differentiation among populations of parasitoids. Generalist parasitoids are expected to be more affected by plant traits (e.g., plant defensive traits) than specialist parasitoids. Data are presented on phenotypic differences of two braconid parasitoid wasps ovipositing on the same insect host species on two different host plant species. Adult mass, adult longevity, and percent parasitism are compared for the generalist parasitoid Cotesia marginiventris Cresson and the specialist parasitoid Aleiodes nolophanae Ashmead (both Hymenoptera: Braconidae) emerging from green cloverworms, Hypena scabra Fabricius (Lepidoptera: Noctuidae), feeding on two host plant species, alfalfa (Medicago sativa L.) and soybean (Glycine max L. Merr.) (both Fabaceae), at three locations. Specialist wasps that parasitized the green cloverworm on alfalfa had a significantly larger mass than the ones that parasitized the green cloverworm on soybean at the three study sites. Generalist wasps that parasitized green cloverworms on alfalfa had a larger mass than wasps parasitizing green cloverworms on soybean only at one of the study sites (i.e., Prince George's County, MD, USA). Similarly, both specialist and generalist wasps lived longer when parasitizing green cloverworms on alfalfa than when parasitizing them on soybean at only one of the study sites (i.e., Prince George's County). In Prince George's County, percent parasitism on alfalfa by the specialist parasitoid was higher than on soybean for three consecutive years and percent parasitism by the generalist parasitoid was the same on alfalfa and soybean every year. Thus, phenotypic differences among populations associated with different host plant species vary geographically (i.e., parasitoid phenotype associated with different host plant species differ at some sites while it is the same at other sites). The implications of geographic variation for biological control are discussed.     

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.