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.

Several species of insects have been indicated as suitable and alternative sources of nutrients for humans and animals. A crucial aspect is that their nutritional composition and development time can be influenced by the substrate used for rearing. The main objective of this study is to evaluate how the fatty acid composition ofTenebrio molitor (Coleoptera: Tenebrionidae) larvae changes with different rearing substrates. For this purpose, a standard diet (51.8% wheat bran + 40.7% soybean meal) was alternatively supplemented with addition of 7.5% (w/w) sunflower, linseed or fish oil. Dry matter, percentage of proteins and lipids, ash and fibre of larvae and substrates, as well as insect development time were determined, highlighting slower growth for insects raised on oil-enriched diets, compared to the control. Gas-chromatography was used to evaluate the fatty acid profile of larvae and substrates. A total of 15 fatty acids was identified and quantified. Palmitic, oleic and linoleic acids were always the most abundant fatty acids detected in larvae, suggesting the presence of physiological regulation mechanisms inT. molitor. The larval content of palmitoleic, oleic, alpha-linolenic and eicosapentaenoic acids was correlated with their content in the rearing diets, indicating strict dependence on diet mainly for PUFA n-3. The n-6/n-3 ratio was influenced by the substrate as well, showing a similar trend between insects and diets but with less variability in larvae. Principal component analysis conducted on the fatty acids profile of larvae displayed several clusters based on the different growing media. This study highlights the importance of the diet in determining the final fatty acid profile of mealworm larvae, although fatty acid enrichment could be dampened by physiological processes of the insects.