This study identified chemicals found on the eggs of two stink bug species, one native to western North America, Euschistus conspersus, and an invasive species from Asia, Halyomorpha halys. The responses of two scelionid egg parasitoids, Trissolcus erugatus and Telenomus podisi, toward natural stink bug egg volatiles, and synthetic reconstructions of egg volatiles, were tested in bioassays. A compound, methyl (2E,4Z)-2,4-decadienoate, previously identified as the major component of the male-produced aggregation pheromone of E. conspersus, was the major volatile identified from extracts of E. conspersus eggs. In contrast, for H. halys, the sesquiterpenoids that compose the male-produced aggregation pheromone of this species were not detected on eggs, whereas the presence of hexadecanal, octadecanal, and eicosanal was detected. In laboratory olfactometer tests, both Tr. erugatus and Te. podisi females were attracted to extracts of E. conspersus eggs, and to synthetic methyl (2E,4Z)-2,4-decadienoate. However, female Tr. erugatus and Te. podisi wasps were repelled, both by extracts of H. halys eggs and by a blend of the aldehydes identified from H. halys eggs. A follow-up field study, using hexane-washed and intact E. conspersus as sentinel eggs, showed that the parasitoids Trissolcus erugatus and Gryon obesum emerged from these eggs. Sentinel hexane-washed eggs treated with 3 ng of methyl (2E,4Z)-2,4-decadienoate were parasitized more by these two species than were hexane-washed or unwashed eggs, whereas hexane-washed eggs treated with a comparable dose of the C16,18,20 aldehyde mixture were avoided by these parasitoids. In a further field experiment, Trissolcus basalis was the primary parasitoid found in sticky traps baited with methyl (2E,4Z)-2,4-decadienoate, indicating that this species was attracted to, but either did not oviposit or develop in the E. conspersus sentinel eggs in the previous experiment.

The egg parasitoid Telenomus podisi is a natural control agent of pentatomids, including Euschistus heros and Tibraca limbativentris, and success of parasitism is dependent upon the parasitoid finding the host. We tested the influence of host egg volatiles and the synthetic sex pheromone (zingiberenol) of T. limbativentris on chemotaxic behaviour of T. podisi, as well as, the impact of the original host on parasitoid selection. We used mated female T. podisi (48 h old) that emerged from the eggs of T. limbativentris or E. heros. The bioassays related to chemotaxy were performed in a Y-tube olfactometer and, to parasitism success, in laboratory and semi-field conditions. Telenomus podisi females that emerged from either the stink bug eggs, chose the pheromone more than control, or the pheromone plus eggs of E. heros in the semi-field bioassay, led to greater parasitism. Females that emerged from E. heros eggs chose egg volatiles from their original host rather than those from T. limbativentris, while females emerging from T. limbativentris, chose the egg volatiles of both hosts equally. When T. limbativentris was the original host, T. podisi females parasitized T. limbativentris over E. heros, while those emerging from E. heros exclusively parasitized E. heros eggs. These results demonstrated that T. podisi is more likely to parasitize the host in which it developed and that the original host can exert influence on the choice by those parasitoids. Understanding how the factors that mediate host-parasitoid communication are interrelated can help biological control programmes establish more effective and reliable tools with T. podisi.

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.

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ABSTRACT. Learning and memory in Telenomus podisi (Hymenoptera, Platygastridae). The egg parasitoid Telenomus podisi Ashmead, 1893 is an important natural control agent of stink bugs. Its success as a parasitoid depends on its host-locating ability, which may be influenced by learning and memory. This study used lemongrass [Cymbopogon citratus (DC.) Stapf. (Poales, Poaceae)] extract to assess the capacity for learning and memory retention time of T. podisi at different developmental stages of the immature phase. Eggs of Euschistus heros (Fabricius, 1798) (Hemiptera, Pentatomidae) parasitized by T. podisi and at different parasitoid juvenile developmental stages were isolated in glass tubes containing filter paper with lemongrass extract or acetone solvent (control). After emergence, T. podisi females were tested in a Y-tube olfactometer containing both scents. Inexperienced females were subjected to the same scents as experienced. To assess memory, females that emerged from eggs that were in contact with lemongrass extract throughout the immature developmental stage were given a choice between lemongrass extract and acetone when they were 24, 48, 72, and 96 hours old. Females that had contact with the lemongrass during the juvenile phase preferred lemongrass, while inexperienced females or those exposed to acetone chose the solvent. The presence of lemongrass all through the immature developmental stage altered the chemotaxic orientation of T. podisi and prompted learning in these organisms that lasted for up to 72 hours. KEYWORDS.Egg parasitoid, experience, biological control, chemotaxy. RESUMO. O parasitoide de ovosTelenomus podisi Ashmead, 1893 é um importante agente de controle natural de percevejos e seu sucesso de parasitismo está associado à habilidade para a localização do hospedeiro, sendo a aprendizagem e a memória um dos fatores que podem influenciar esta interação. O trabalho avaliou a capacidade de aprendizagem e tempo de retenção da memória de T. podisi ao extrato de capimlimão [Cymbopogon citratus (DC.) Stapf. (Poales, Poaceae)], em diferentes estágios do desenvolvimento da fase imatura. Ovos de Euschistus heros (Fabricius, 1798) (Hemiptera, Pentatomidae) parasitados por T. podisi foram individualizados em tubos de vidro contendo papel filtro com extrato de capim-limão ou solvente acetona (controle) e mantidos em diferentes estágios do desenvolvimento jovem dos parasitoides. Após a emergência, fêmeas de T. podisi foram testadas em olfatômetro tipo "Y" aos odores de ambos tratamentos. Fêmeas inexperientes foram submetidas aos mesmos odores das experientes. Para avaliar a memória, fêmeas oriundas de ovos que permaneceram em contato com o extrato de capim-limão por todo o desenvolvimento do estágio imaturo, foram testadas, após 24, 48, 72 e 96 horas de idade ao odor de capim-limão e acetona. Fêmeas que permaneceram em contato com o capim-limão por toda a fase jovem, direcionaram-se preferencialmente para este extrato, diferente das inexperientes ou das expostas à acetona, as quais preferiram o solven...