Oviposition behavior of Trichogramma platneri Nagarkatti and Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) in patches of single and clustered host eggs

Commercially produced Trichogramma species are widely used in augmentative biological control programs. Here, we test whether two North American species, Trichogramma platneri and Trichogramma pretiosum, that differ significantly in potential fecundity (Mills and Kuhlmann, 2000), also differ in their response to and efficiency of use of single and clustered host eggs. The ovipositional behavior of individual experienced parasitoid females was monitored continuously in patches (3.5 × 3.5 cm card) with 16 single spaced or clustered eggs of Ephestia kuehniella Zeller at 25 °C for up to 1 h or until the female left the patch. The ovipositional behavior of each parasitoid species in each patch type was summarized as generalized ethograms, patterns of patch use, time budgets, and the sequence of sex allocation. T. platneri parasitized fewer eggs with a lower rate of oviposition, and a greater oviposition time per egg in patches with clustered eggs than in patches with single eggs. In contrast, the number of eggs parasitized and the oviposition time per egg were equal in both patch types for T. pretiosum, but the rate of oviposition was greater and residence time reduced in patches with clustered eggs. In single egg patches the first egg to be laid had a high probability of being male for both parasitoid species, with the subsequent four eggs having an increasing probability of being female. In clustered egg patches, a male egg was most likely to be produced second in the sequence by T. pretiosum, whereas T. platneri showed a marked alternation of sexes over the sequence of the first five eggs laid. The more efficient use of host egg clusters by T. pretiosum than by T. platneri suggests that closer attention should be paid to matching the ovipositional behavior of Trichogramma species to the oviposition strategy of the target pest.