Egg parasitoids have evolved adaptations to exploit host-associated cues, especially oviposition-induced plant volatiles and odors of gravid females, when foraging for hosts. The entire host selection process is critical for successful parasitism and relevant in defining host specificity of parasitoids. We hypothesized that naïve egg parasitoid females reared on their coevolved host are able to exploit cues related to the coevolved host but not those from a novel host. We used the egg parasitoid Trissolcus japonicus , its coevolved host Halyomorpha halys , and the non-coevolved host Podisus maculiventris to evaluate this hypothesis. H. halys , a polyphagous pest native from Eastern Asia, has invaded North America and Europe, resulting in serious damage to crops. T. japonicus is the most effective egg parasitoid of H. halys in its native area and thus considered a major candidate for biological control. This parasitoid was detected in North America and Europe as a result of accidental introductions. Laboratory host range of T. japonicus includes P. maculiventris, an American predatory stink bug used as a biological control agent of several pests. Using T. japonicus reared on its natural host H. halys , we tested in a Y-tube olfactometer the responses of naïve parasitoid females to volatiles from tomato plants with a deposited egg mass and feeding punctures of either H. halys or P. maculiventris . Additionally, using two different olfactometer set-ups, we tested T. japonicus responses to volatiles emitted by eggs and mature males and females of H. halys or P. maculiventris . Tomato plants subjected to oviposition and feeding by H. halys were preferred by the wasp compared to clean plants, suggesting a possible activation of an indirect defense mechanism. Furthermore, T. japonicus females were attracted by cues from gravid females and mature males of H. halys but not from eggs. By contrast, naïve parasitoid females never responded to cues associated with P. maculiventris , although this non-target host is suitable for complete parasitoid development. Such lack of responses might reduce the probability of T. japonicus locating and parasitizing P. maculiventris under field conditions. Our experimental approach properly simulates the parasitoid host-location process and could be combined with the required host specificity tests for risk assessment in biological control programs.

When an accidentally introduced pest establishes in the invaded area, native natural enemies may adapt to the new host. A decade after the accidental introduction of the brown marmorated stink bug, Halyomorpha halys, in Europe, two generalist native egg parasitoids, the eupelmid Anastatus bifasciatus and the encyrtid Ooencyrtus telenomicida, have been recorded from this invasive agricultural pest in the field. Both species are able to complete development to the adult stage within the new host. Trissolcus basalis (Platygastridae = Scelionidae), which is not associated with H. halys in the field, was reared from freeze-killed sentinel eggs placed on soybean plants in central Italy. We tested in a Y-tube olfactometer the behavioural responses of these egg parasitoids to volatiles from H. halys adults and from Vicia faba plants attacked by H. halys. Both A. bifasciatus and O. telenomicida positively responded to adult H. halys male volatiles and to H. halys-induced plant volatiles, indicating ability to exploit cues associated with the new host for egg location, whereas T. basalis only reacted to female volatiles. A. bifasciatus and O. telenomicida are generalist egg parasitoids, showing a much wider host range when compared to T. basalis. On the other hand, platygastrid egg parasitoids from the native area of H. halys, considered for classical biological control, may be too risky due to the possibility of attacking non-target species, including predaceous stink bugs. Therefore, indigenous A. bifasciatus and O. telenomicida are presently under evaluation for augmentative biological control of H. halys in Europe

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Despite the fact that natural enemies can synergistically contribute to herbivore pest suppression, sometimes predators engage in intraguild predation (IGP) that might dampen trophic cascades. DNA-based gut-content analysis has become common in assessing trophic connections and biocontrol potential by predators in field systems. Here, we developed a molecular technique that can be used to unravel predation among two ladybirds, Coccinella septempunctata and Hippodamia variegata, and their shared prey, Aphis gossypii. Both ladybirds may provide effective control of the pest. Therefore, understanding their likelihood to engage in IGP is crucial for conservation biological control. Ladybird specimens were collected in melon crop. DNA extraction, primer design and evaluation were conducted. Detectability of prey DNA did not differ significantly between the two ladybirds. H. variegata exhibited higher predation on A. gossypii than C. septempunctata (90.6% vs. 70.9%) and data correction based on DNA detectability confirmed this ranking. IGP was similar among the two species, although corrected data might suggest a stronger predation by C. septempunctata. Intriguingly, IGP by C. septempunctata was lower than predicted by laboratory bioassays, possibly due to the high complexity that arises under field conditions. Implications of our results for biological control and perspectives for ecological network analysis are discussed.