EFFECTS OF PHYSICAL AND CHEMICAL SIGNALS ON HOST FORAGING BEHAVIOR OFDRINO-INCONSPICUA (DIPTERA, TACHINIDAE), A GENERALIST PARASITOID

Host-foraging behavior of the tachinid parasitoid, Drino inconspicua M eigen (Diptera: Tachinidae), was studied by laboratory bioassays to el ucidate the role of physical and chemical factors for host finding and recognition. Larvae of the European spruce sawfly, Gilpinia hercyniae Hartig (Hymenoptera: Diprionidae), were used as hosts. While volatile s of spruce twigs with feeding sawfly larvae did not attract the paras itoid, movements of host larvae and of dummies of the host significant ly elicited a positive response at short range. Females of D. inconspi cua showed a direct walking behavior to a moving object at distances o f 9-10 cm. The maximum distance at which the parasitoids were attracte d by movement was 16 cm. At short range, parasitoid females preferred to contact a moving larval dummy made of filter paper rather than an u nmoved dummy or an unmoved freshly killed larva of G. hercyniae. The t achinid females which were reared from C. hercyniae larvae showed no p reference for this host species when compared with larvae of Diprion p ini L. (Hymenoptera: Diprionidae) and the unnatural host species Galle ria mellonella L. (Lepidoptera: Pyralidae). Furthermore, D. inconspict ua did not prefer certain instars of G. hercyniae for oviposition. The role of cuticular chemicals of G. hercyniae larvae for host acceptanc e was tested by offering host larvae washed with solvents of different polarities and unwashed larvae. Each tested parasitoid female readily accepted both treated and untreated larvae for oviposition. When a he xane extract of the cuticle of host larvae was applied to a dummy, ovi positing D, inconspicua did not significantly distinguish between a tr eated dummy and a control dummy. Whereas the parasitoid's response to dummies offered as oviposition sites did not depend on the presence of cuticular extracts of hosts, the softness of the dummies was crucial. The parasitoid females significantly preferred soft dummies (hardines s unit [HU]:0.05 +/- 0.01 Nmm(-2)) to hard ones (HU: 207.72 +/- 6.16 N mm(-2)) for oviposition. Thus, physical factors like movement of the h ost and its softness clearly play a major role in host foraging of D. inconspicua rather than chemical signals of the host or its host plant .