Host and host age preference of Trichogramma galloi and T-pretiosum (Hymenoptera : Trichogrammatidae) reared on different hosts

Experiments were conducted to investigate the host and host age preference of Trichogramma galloi Zucchi and T. pretiosum Riley when reared from the e ggs of Diatraea rufescens Box (Lepidoptera: Pyralidae), D. saccharalis F., or Sitotroga cerealella Olivier (Lepidoptera: Gelechiidae). The effect of t he host on host preference was weak or absent, because the majority of the test females of both Trichogramma species attacked eggs of a certain host f irst. T. galloi females did not recognize eggs of S. cerealella as a potent ial host, suggesting that females of this species need additional olfactory cues for host recognition. Furthermore, relative host size had a noticeabl e effect on choice of the first host by T, galloi. The larger eggs of D. ru fescens were preferred over eggs of D. saccharalis. This was not the same f or females of T. pretiosum; the majority of them attacked the small eggs of S. cerealella first. Eggs of D. rufescens were accepted to a lesser extent and eggs of D. saccharalis were rejected. In choice experiments, females o f T, galloi consistently preferred younger eggs of D. rufescens over older ones. In nonchoice situations, only 4-d-old host eggs were parasitized less commonly by both T. galloi and T. pretiosum and had a lower number of prog eny allocated to them. Five-day-old hosts were never parasitized. Neverthel ess, there was a clear-cut relation between host age and time lapse before the Ist host acceptance. The implications of these results for learning in Trichogramma. and for candidate species selection in biological control are discussed.