Host age preference behaviour of Trichogramma aurosum Sugonjaev & Sorokina (Hymenoptera: Trichogrammatidae)

Host age selection in several German strains of Trichogramma aurosum Sugonjaev & So-rokina was examined in laboratory choice tests under direct observation for 90 min., in order to select candidate strains for attempts at controlling the codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae). Experiments were conducted at room tempera-ture by exposing combinations of two host ages (zero vs. four and one vs. five-days old) to a single female wasp. Host age did not appear to affect the wasps parasitization be-haviour, although they spent longer time drilling on old eggs (four and five days old) compared with fresh ones (zero and one day old). This not necessarily means that they preferred fresh eggs over old ones, since both type of hosts were parasitized in the choice test. Possibly an increased mechanical resistance of the chorion of older eggs was responsible for the prolonged drilling time. Mean drumming time was independent of host age. Mean duration of drilling and drumming was in general longest in the first and last egg attacked by all T. aurosum strains tested and for all host ages. Drilling time made more than 80% of the mean handling time of all strains tested for all host ages, fol-lowed by resting and walking.