pay-off superparasitism in the egg parasitoid Trissolcus basalis, in relation to patch defence

In species such as quasi-gregarious egg parasitoids which exploit defendable patches, the fitness pay-off from superparasitism is an important factor in considering the evolution of patch defence and optimal patch defence strategies. When oviposition in a previously parasitized host has a non-zero fitness pay-off, competing parasitoids are not only able to diminish the future value of a patch to other females by depleting unparasitized hosts, but also devalue the previous investment of other females in the patch by superparasitizing. In Trissolcus basalis, an egg parasitoid of pentatomid bugs, the fitness pay-off from superparasitism is higher than 0.5 when the time interval between ovipositions is less than 3 h, suggesting that defending a previous investment will be an important component of patch defence behaviour. The data suggest a mechanism for the high early pay-off, which involves the superparasitizing female adjusting the sex ratio of its offspring in favour of males. Males develop more quickly than females and thus may have a competitive advantage.