Effects of temporary host deprivation on the reproductive potential of Trichogramma brassicae

Abstract

AbstractThe effect of host deprivation on the reproductive potential and parasitization behaviour of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) was investigated. Upon emergence, females were deprived of hosts for one to four days, and were subsequently provided with an unlimited number of hosts. Regardless of its duration, deprivation did not affect female longevity, overall rate of progeny emergence, or progeny sex‐ratio. As deprivation time increased, however, the total number of parasitized hosts decreased from an average of 81.2 when hosts were provided at emergence, to an average of 34.0 when the waiting time was 4 days. This reduction was mainly due to the reduction in the parasitizations following the first laying peak, which was not affected when deprivation lasted fewer than 4 days. Trichogramma females are able to store ripe eggs (about 35) for 3 days without damage, but resorption occurs after four days of deprivation. Our results suggest that imaginal vitellogenesis occurs in this proovigenic wasp but that it is affected by host deprivation. The behaviour of females, as measured by the average distance between all parasitized hosts, was also modified by host deprivation. When deprivation exceeded one day, parasitizations were more scattered over the host patch. Moreover, increased deprivation times also appeared to delay the initiation of parasitization by a few hours.Host shortage is likely to occur in nature, reducing the efficiency of Trichogramma as a biocontrol agent. The individual history of females must be taken into account in any study of the reproductive strategies of parasitoid females.