Long-term egg retention and parasitization in Trichogramma principum (Hym., Trichogrammatidae)

Laboratory experiments with Trichogramma principium Sug. et Sor. females th at were offered Sitotroga cerealella Oliv. eggs demonstrated that less than half of the ovipositing females started oviposition during the first 2 day s of the experiment, whereas the rest of the ovipositing females showed a d elay in parasitization ranging from 2 to 10 days after contact with the hos e. Almost 10% of the wasps refused to parasitize the grain moth eggs over 1 2 days. The delay in parasitization may be as long as 6-8 days without any significant decrease in the number of mature ovarial eggs, in the number of eggs laid during the first 48 h of oviposition, and in the total lifetime fecundity. This egg retention is responsible for the fact that in spite of a relatively short mean duration of the oviposition period in each individu al female (approximately 4 days), host parasitization by a group of simulta neously emerged wasps was almost uniformly distributed over 8-10 days. When induced, the parasitization state (i.e. the tendency to parasitize sequent ially offered portions of host eggs) was stable both in the presence of a h ost and under host deprivation extended up to 8 days. These data provide fu rther evidence for our hypotheses that the stability of the parasitization state in Trichogramma is based on endocrine mechanisms.