Responses of the Egg Parasitoid Psix saccharicola towards Volatiles from the Pistachio Green Stink Bug Acrosternum arabicum

Egg parasitoids have evolved various strategies to overcome the reliability-detectability problem and efficiently parasitize host eggs. Identifying what cues egg parasitoids use is important to increase their efficiency as biocontrol agents. In this study, we investigated the role of chemical cues from eggs and defensive compounds of the pistachio green stink bug (PGSB), Acrosternum arabicum (Hemiptera: Pentatomidae), on the foraging behavior and adult sex discrimination by the egg parasitoid Psix saccharicola (Hymenoptera: Scelionidae). Parasitoid responses to volatiles from PGSB egg masses and sex-specific metathoracic gland (MTG) extracts were evaluated using a Y-tube olfactometer. We found that P. saccharicola was significantly attracted to volatiles emitted by egg masses and to MTG extracts from both sexes. However, parasitoids did discriminate between males and females by displaying longer residence times in the arm containing the female MTG extract. Gas chromatography analysis showed that MTG and egg masses extracts contained largely similar chemical profiles, consisting of various alkanes, aldehydes and esters, with the major compounds being tridecane, (E)-2-decenal, and (E)-2-decenyl acetate. Our SEM analysis suggest that MTG secretions are passively deposited onto the eggs. Together, our findings suggest that PGSB volatile compounds from the MTG attract the egg parasitoid, which may be useful in developing semiochemical-based biological control strategies against PGSB.