Egg retention in the presence of a host in Trichogramma females

Laboratory experiments with Trichogramma principium suggest that Trichogram ma females may be in one of two alternative states: the parasitization stat e or the egg retention state. Dissections show that T. principium females a t emergence have approximate to 20 mature ovarian eggs. Females in egg rete ntion state have practically the same mean number of mature ovarian eggs, w hile the distribution is different, suggesting that both oosorption and oog enesis may occur during egg retention. In parasitizing females, additional maturation starts simultaneously with the oviposition. However, ovipositing females tend to lay eggs with maturation, which is why they mostly carry f ew(< 5) mature ovarian eggs. The mean number of eggs laid during the first 48 h of the oviposition does not depend on whether the parasitization is de layed or not, suggesting that egg retention is connected just with oviposit ion behaviour rather than with the intensity of oogenesis. We conclude that 'voluntary' egg retention in the presence of a host does not differ with t he state of ovaria from 'forced' egg retention under host deprivation. Supp osedly, egg retention with the availability of a suitable host may be consi dered as a sort of short-term adult diapause-like state when not oogenesis, but oviposition is subject to hormonal regulation.