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.     

Response of the parasitoid Telenomus podisi to induced volatiles from soybean damaged by stink bug herbivory and oviposition

Abstract

Egg parasitoids have a short time frame in which their host eggs are suitable for parasitism, and in several systems these parasitoids respond to plant volatiles induced by oviposition on the plant (either in isolation or in combination with feeding damage) as a means of finding suitable hosts. It is known that the parasitoid of pentatomid eggs Telenomus podisi responds to damage done to soybeans by female Euschistus heros, its preferred host. In this study our aim was to determine the type of E. heros damage to soybean (herbivory, oviposition or a combination of both) necessary for attraction of T. podisi. In a Y-tube olfactometer the parasitoid has shown to respond to the undamaged plant over clean air and herbivory-damaged plants over undamaged plants. However, the parasitoids did not respond to the treatments where oviposition occurred, either in isolation or in combination with herbivory. Analysis of volatile blends revealed that herbivory plus oviposition damage to soybean induced a volatile blend different to those induced when herbivory or oviposition occurred separately. These results, along with other results from this system, suggest that T. podisi uses plant volatile cues associated with female E. heros damage in order to be present when E. heros lays its eggs, and thus ensure its resource is optimal for parasitism.     

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.     

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.     

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.     

Storage of Pentatomid Eggs in Liquid Nitrogen and Dormancy of Trissolcus basalis (Wollaston) and Telenomus podisi Ashmead (Hymenoptera: Platygastridae) Adults as a Method of Mass Production

The eggs of pentatomid species were evaluated to parasitism by Trissolcus basalis (Wollaston) and Telenomus podisi Ashmead after storage in liquid nitrogen. Adults which emerged from stored eggs were kept at 18°C for 120 and 180 days to investigate whether adult dormancy could be associated with host egg storage in liquid nitrogen as a method of mass production of these egg parasitoids. Eggs of Nezara viridula (L.) and Acrosternum pengue (Rolston) were successfully parasitized by T. basalis, as well as Piezodorus guildinii (Westwood) and Dichelops furcatus (F.) by T. podisi. The eggs of Edessa meditabunda (F.) were not parasitized by T. basalis. The emergence of T. podisi from eggs of Euschistus heros (F.) and Podisus nigrispinus (Dallas) stored for 6 months was lower than the control. Females of T. basalis and T. podisi that emerged from stored eggs were kept in dormancy at 18°C. Longevity of T. basalis was influenced by the storage time and sex, but not by the interaction of sex and storage time. For T. podisi, longevity was influenced by the storage time, sex, and by the interaction of sex and storage time. For T. basalis, storage in liquid nitrogen did not affect the fecundity of quiescent females, while the number of parasitized eggs by T. podisi decreased after storage. By the joint use of these techniques, it is possible to optimize mass production of T. basalis so that its life cycle can be monitored and synchronized with the life cycle and availability of hosts.     

Effect of host egg viability on reproduction and development of Trichogramma cacoeciae and T. principium (Hymenoptera: Trichogrammatidae)

A combination of a sterile insect technique, resulting in infertile eggs, and of an egg parasitoid, should provide better control of codling moth than either alone. Non-choice laboratory experiments were conducted with infertile and fertile codling moth eggs to evaluate the potential parasitism and reproduction of Trichogramma cacoeciae Marchal and T. principium Sug. et Sor. The tendency of T. cacoeciae females to attack infertile eggs was similar to that for fertile eggs, whereas T. principium showed a greater preference for infertile eggs than fertile eggs. The fertility status of the host did not affect the number of eggs that were parasitized but fewer F₁ progeny emerged from infertile eggs when parasitized than from fertile eggs. When T. cacoeciae and T. principium parasitized infertile host eggs their mean developmental time was prolonged but the viability and quality of parasitoid progeny was not influenced by the fertility status of the host eggs. The study demonstrates the compatibility of use of T. cacoeciae and T. principium in an integrated program employing the sterile insect technique for codling moth management.     

Effects of storage at low-temperature of various heteropteran host eggs on the egg parasitoid, <Emphasis Type="Italic">Trissolcus semistriatus</Emphasis>

Various heteropteran host eggs stored under two low-temperatures were tested in the laboratory for their usability in the production of sunn pest egg parasitoid, Trissolcus semistriatus. Parasitism, adult emergence rate and development time were assesed on stored and fresh eggs of Eurygaster integriceps, Dolycoris baccarum, Graphosoma lineatum and Eurydema ornatum. Masses of fresh host eggs in microcentrifuge tubes were maintained at +6 °C and −20 °C. Every 30 days, 50 eggs of host species were exposed to parasitism by T. semistriatus. The host eggs stored at 6 °C remained viable to parasitism by T. semistriatus up to 2 months, while those of stored at −20 °C were parasitized at high rates up to 4 months, alhough succesful parasitism rates decrease with time. However, it was indicated that both fresh or stored E. ornatum eggs were not preferred to parasitism by the parasitoid. A longer development time from egg to adult was observed in stored eggs under two tested storage techniques when compared with fresh eggs.     

Olfactory responses of Anaphes nitens (Hymenoptera,Mymaridae) to host and habitat cues

The eucalyptus weevil, Gonipterus spp. Schoenherr, 1833 (Coleoptera, Curculionidae) is considered a major pest of eucalyptus plantations. In regions where control is achieved, success is usually brought by the action of the solitary egg parasitoid Anaphes nitens (Girault, 1928) (Hymenoptera, Mymaridae). Research was conducted to ascertain which cues might mediate female wasp host location and selection. In Petri dish arenas, females were attracted to Gonipterus platensis Marelli, 1927 egg capsules, to G. platensis mated female faeces and to leaves of Eucalyptus globulus Labillardière, 1799. Gas chromatography–mass spectrometry electroantennographic detection analysis was conducted using extracts obtained from leaves of E. globulus, from G. platensis egg capsules, as well as from adults of both sexes and their faeces, in order to detect and identify compounds perceived by the wasp's olfactory system. The parasitoids were shown to detect a wide range of compounds emitted by each one of these sources, and for 31 compounds, antennal response was confirmed by dose-response tests. Further behavioural trials were conducted in Petri dishes in order to decode the effect, on parasitoid behaviour, of selected compounds emitted by E. globulus and of the pheromones, emitted by the weevils on parasitoid behaviour. Attraction was observed to two compounds emitted by E. globulus, namely 1,8-cineole and γ-terpinene, and to the main component of the male sex/aggregation pheromone, cis-verbenol. To our knowledge, this is the first report of attraction of a parasitoid from the family Mymaridae to a component of its host's sexual/aggregation pheromone. Similarly, to other egg parasitoid species, A. nitens females are likely to use the host plant volatiles as long-range host location cues and to adopt the ‘infochemical detour’ strategy in order to get in the vicinity of their hosts.     

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.     

In vitro rearing of Ooencyrtus nezarae (Hymenoptera: Encyrtidae), an egg parasitoid of Riptortus pedestris (Hemiptera: Alydidae)

Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) is a polyphagous egg parasitoid of various true bugs, including Riptortus pedestris (Fabricius) (Hemiptera: Alydidae), a major pest of soybean and fruit trees in northeastern Asia. This study was conducted to develop artificial host eggs containing insect haemolymph for mass rearing of O. nezarae. The haemolymph of Chinese oak silkworm (Antheraea pernyi Guérin-Méneville) pupae was found to be most suitable for artificial eggs for the complete development of O. nezarae. Among 764 parasitoid eggs laid in artificial eggs, 49.2% successfully developed to adult parasitoids. The developmental time in artificial eggs was delayed by 3–5 days relative to that observed in natural host eggs; however there was no significant difference in the length of hind tibia between adults that emerged from artificial and natural host eggs. Moreover, new generations that emerged from artificial eggs reproduced on all egg types offered (either natural or artificial eggs). We propose that the artificial eggs developed herein can therefore be an effective means for mass rearing O. nezarae.     

Refrigeration of Riptortus clavatus (Hemiptera: Alydidae) eggs for the parasitization by Gryon japonicum (Hymenoptera: Scelionidae)

Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) is a solitary egg parasitoid of Riptortus clavatus (Thunberg) (Hemiptera: Alydidae) one of the most important pests in soybean in Korean and Japan. Refrigeration of R. clavatus eggs for up to 120 days was evaluated as a method of mass production of G. japonicum. The refrigeration reduced the eclosion of eggs, thus no nymph emerged after 30 days of egg refrigeration. Increased duration of host acceptance behaviors by G. japonicum and some detrimental effects on parasitism rate, developmental time, longevity, and adult size of the parasitoid were found in refrigerated host eggs. However, all the biological parameters of G. japonicum were unaffected by the refrigeration of up to 30 days. Gryon japonicum parasitized 16 and 14 host eggs daily that were refrigerated for 15 and 30 days, respectively, which did not differ from parasitization of fresh host eggs. Furthermore, refrigeration of host eggs did not reduce the reproduction of the emerged adult parasitoids and emergence and sex ratio of their progeny. Gryon japonicum also parasitized 14 and 13 refrigerated host eggs per day kept at 26.3°C and 78.7% RH for 2 and 4 days of post-refrigeration without significant reduction, respectively. These results show that refrigeration of R. clavatus eggs can be a good method for mass rearing of the parasitoid, and the host eggs killed by cold storage can be supplemented in the field to boost field parasitism.     

Effect of host deprivation on egg quality,egg load,and oviposition in a solitary parasitoid,Chetogena edwardsii (Diptera: Tachinidae)

Solitary parasitoids are limited to laying one egg per host because larvae compete within hosts. If host encounter rate is low, females should not increase the number of eggs/host in response. The tachinid fly, Chetogena edwardsii,was used to evaluate the effect of host deprivation on egg accumulation, oviposition behavior, and egg quality in a solitary parasitoid. Females deprived of hosts for 2– 7 days accumulate about 1 day's supply of eggs. Egg output of deprived females once hosts are restored does not differ from that of control females. Deprived females retain one egg in the uterus where it undergoes embryogenesis. Maggots emerging from retained eggs are more likely to survive in hosts molting in 40 h or less after receipt of an egg than are maggots emerging from eggs fertilized shortly before oviposition. Egg retention is a consequence of host deprivation that permits females to broaden the range of hosts they can exploit to include soon-to-molt hosts and possibly multiply parasitized hosts.     

Influence of Host Pheromone on Egg Parasitism by Scelionid Wasps: Comparison of Phoretic and Nonphoretic Parasitoids

The kairomonal activity of the attractant pheromone for the spined soldier bug, Podisus maculiventris (Hemiptera: Pentatomidae), was investigated by exposing fresh pentatomid egg masses in field traps with or without synthetic pheromone. Predominantly two parasitoids were recovered from exposed eggs of P. maculiventris and Euschistus obscurus: Telenomus podisi Ashmead (a generalist pentatomid egg parasitoid) and Telenomus calvus Johnson (a phoretic specialist on Podisus eggs) (Hymenoptera: Scelionidae). The incidences of T. podisi from P. maculiventris and E. obscurus eggs placed in pheromone-baited and nonbaited traps were not significantly different, suggesting that this oophagous wasp does not use the spined soldier bug attractant pheromone as a kairomone. However, T. calvus was reared almost exclusively from egg masses of P. maculiventris placed inside pheromone-baited traps. These results suggest that T. calvus females orient to volatile chemicals emitted by spined soldier bug males as a searching strategy to find areas likely to contain host eggs, in addition to the previously discovered strategy of using the pheromone to guide their phoretic behavior. The data also indicate that T. calvus can distinguish between the egg masses of these pentatomid hosts at close range.     

Mediterranean flour moth Ephestia kuehniella eggs and larvae exposed to a static magnetic field and preference by Trichogramma embryophagum

This study investigated the effect of strong magnetic fields as insecticidal activity on Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) larvae and eggs at different stages of development and their preference by the egg parasitoid, Trichogramma embryophagum Hartig (Hymenoptera: Trichogrammatidae). Eggs ranging in age from 24-h to 48-h and 72-h-old and larvae (1 to 2 days) were exposed to 1.4 Tesla (T) magnetic fields from a DC power supply at 50 Hz for different time periods (3, 6, 12, 24, 48 and 72 h). Twelve hours of exposure at 1.4 T was toxic to 24-h-old eggs of E. kuehniella. The 72-h-old host eggs treated with 1.4 T for 6–72 h were not significantly preferred by T. embryophagum. The magnetic field was toxic to 24-h-old eggs of E. kuehniella exposed to 1.4 T for 12. The treatment of magnetic fields on the 72-h-old host egg with 1.4 T at 6–72 h was not significantly preferred by T. embryophagum. Magnetization of 24-h-old eggs of E. kuehniella for 3 h could be effectively used with T. embryophagum as sterilised host eggs. These eggs were markedly preferred by T. embryophagum. The LT₅₀ and LT₉₉ values of magnetic fields at different egg stages of E. kuehniella, and larvae were measured. A level of 1.4 T at 72 h completely prevented the development of the larvae. There was no significant effect on larval survival at 1.4 T at 48 and 72 h. Increasing magnetic fields exposure times for eggs that were 24-h, 48-h and 72-h-old prevented larval emergence and increased their mortality rate. Consequently, magnetic fields could be used in controlling stored-product pest eggs and larvae of E. kuehniella.     

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.     

Host preference: parasitism, emergence and development of Trissolcus semistriatus (Hym., Scelonidae) in various host eggs

Abstract: Trissolcus semistriatus is an important egg parasitoid of the sunn bug, Eurygaster integriceps. Conservation and the supportive augmentation of populations of egg parasitoids appears to offer high potential for the biological control of sunn bug in an integrated pest management system. The present study was conducted to determine the host preference of T. semistriatus on various heteropteran host eggs. When each host species was examined separately, the eggs of E. integriceps, Dolycoris baccarum, Graphosoma lineatum, Carpocoris pudicus and Holcostethus vernalis, were parasitized at high levels, namely 88.0, 83.6, 94.8, 87.3 and 80.8%, respectively, whereas a smaller portion of Eurydema ornatum eggs were parasitized (24.0%). There was no parasitism in Nezara viridula eggs by T. semistriatus. Similar high rates were recorded for the percentage of adult emergence in each host species, with the exception of E. ornatum. The average development time was shorter for males than for females. The average development period for both male and female was significantly longer in eggs of E. ornatum than in those of the other host species. These results and observations recorded during the experiments showed that G. lineatum and D. baccarum were available, cheap hosts and it was demonstrated that these hosts could be used for the mass production of egg parasitoids.     

Host location by the gerrid egg parasitoidTiphodytes gerriphagus (marchal) (Hymenoptera: Scelionidae)

Mechanisms used by a scelionid egg parasitoid to locate its gerrid host eggs were studied using field experiments. Parasitism by Tiphodytes gerriphaguswas higher in exclosures containing adults of Limnoporus dissortisthan in cages without gerrids. Higher densities of adult gerrids were associated with higher rates of parasitism, but dispersion of aquatic vegetation did not apparently affect rates of parasitism. T. gerriphagusmay use visual cues, chemical cues, or a combination of both to locate their hosts. We discuss the possible influence of T. gerriphaguson the reproductive behavior of its hosts.     

The role of host semiochemicals in parasitoid specificity: a case study with Trissolcus brochymenae and Trissolcus simoni on pentatomid bugs

The role of semiochemicals on host specificity of two egg parasitoid species, the European Trissolcus simoni and the American Trissolcus brochymenae (Hymenoptera: Scelionidae), was studied in an olfactometer and in different arenas. Cues from two allopatric pests of cabbage, the European Eurydema ventrale and the American Murgantia histrionica (Heteroptera: Pentatomidae), and from the polyphagous and cosmopolitan Nezara viridula were tested. Both T. simoni and T. brochymenae responded to volatile and contact cues from their co-evolved hosts E. ventrale and M. histrionica, respectively, thus confirming the role of host semiochemicals in host location and recognition. When cues of non-co-evolved hosts were presented, a partial “new association” was obtained, as T. simoni probed and oviposited in M. histrionica eggs and some adult emergence occurred. However, this association is unlikely to occur in the field because T. simoni did not respond to volatile cues of M. histrionica. Instead T. brochymenae partially responded to volatile and contact cues from E. ventrale, but eggs were rarely accepted and parasitoids did not develop in this host. When N. viridula was tested, T. simoni responded only to contact cues, whereas T. brochymenae partially responded to volatile and contact cues, but N. viridula eggs were not suitable for development. Therefore, the N. viridula–T. brochymenae association reported from the literature appears unreliable. Understanding the mechanisms that result in host specificity may help increase parasitoid safety and predict their efficacy in biological control with old or new associations.