EFFECT OF HOST AVAILABILITY ON REPRODUCTION AND SURVIVAL OF THE PARASITOID WASP TRICHOGRAMMA-MINUTUM

1. We tested the hypothesis that females of the egg parasitoid, Tricho gramma minutum Riley (Hymenoptera: Trichogrammatidae), could adjust th eir fecundity schedule according to host availability and that there w as a negative correlation between reproduction and survival in these w asps. 2. Newly-emerged females were provided with an unlimited or limi ted number of hosts in the first trial and with either unlimited, limi ted or zero hosts in the second trial. 3. When hosts were unlimited, w asps had the highest rate of reproduction in the first day, which decr eased dramatically thereafter. When hosts were limited, wasps from the two trials differed in their response. In Trial I, females with limit ed hosts had lower first-day fecundity than, and the same subsequent-d ay fecundity as, those with unlimited hosts. However, in Trial II, fem ales with limited host had a lower first-day but a higher subsequent-d ay fecundity than those with unlimited hosts. This indicates variation in Trichogramma's ability to shift its fecundity schedule in response to host availability. 4. 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 c ould not (in host-unavailable treatment). 5. The sex ratio of the prog eny produced by wasps in both host-unlimited and limited treatments sh ifted gradually from a female to a male bias as the wasps aged. 6. 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.