Effect of host availability on reproduction and survival of the parasitoid wasp Trichogramma minutum

Abstract

Abstract. We tested the hypothesis that females of the egg parasitoid, Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae), could adjust their fecundity schedule according to host availability and that there was a negative correlation between reproduction and survival in these wasps. Newly‐emerged females were provided with an unlimited or limited number of hosts in the first trial and with either unlimited, limited or zero hosts in the second trial. When hosts were unlimited, wasps had the highest rate of reproduction in the first day, which decreased dramatically thereafter. When hosts were limited, wasps from the two trials differed in their response. In Trial I, females with limited hosts had lower first‐day fecundity than, and the same subsequent‐day fecundity as, those with unlimited hosts. However, in Trial II, females with limited host had a lower first‐day but a higher subsequent‐day fecundity than those with unlimited hosts. This indicates variation in Trichogramma's ability to shift its fecundity schedule in response to host availability. There was a positive (rather than a negative) correlation between reproduction and survival. Wasps that oviposited (in host‐unlimited treatment) had greater longevity than those that could not (in host‐unavailable treatment). The sex ratio of the progeny produced by wasps in both host‐unlimited and limited treatments shifted gradually from a female to a male bias as the wasps aged. We consider the ability of parasitoids to adjust their fecundity schedule as an adaptation to changing host resources and discuss our findings with regard to theories of life history evolution.