Host location of Hyssopus pallidus, a larval parasitoid of the codling moth, Cydia pomonella

The effectiveness of parasitoids as biological control agents depends large ly on their host location behavior. In this study we describe the host-sear ching behavior of Hyssopus pallidus (Askew), a larval parasitoid of the cod ling moth Cydia pomonella L. We observed parasitold behavior on mature appl es (a potential host patch) and elucidated some of the stimuli which determ ine host location. Female wasps showed more complex and intensive searching on infested apples than on mechanically damaged or noninfested apples. Was ps were able to enter infested apples through the calyx or the tunnel made by the host larvae and parasitize them. Area-restricted searching was obser ved on infested apples, in particular on areas contaminated with host frass . In a further bisassay, we confirmed that host frass contains a host locat ion kairomone. The kairomone appears to be produced by the host independent ly from its diet, even though frass produced by hosts fed on an apple are m ore attractive than frass produced by hosts fed on a fruit-devoid artificia l diet. The capability of H. pallidus to locate its host inside apples make s the foraging strategy of this species potentially useful as a biological control agent. (C) 1999 Academic Press.