Using sex ratios to estimate what limits reproduction in parasitoids

The reproductive success of a foraging parasitoid may be limited by the num ber of eggs that she produces and/or the number of hosts that she can locat e. Despite the significance for population dynamics and numerous areas of b ehavioural ecology, the relative importance of these factors remains an iss ue of contention. Attempts to resolve this controversy have been hindered b ecause estimating the importance of factors limiting reproduction in the fi eld can be extremely laborious and time consuming. We show how sex ratio da ta can be used as a relatively easy method to indirectly estimate the relat ive importance of the factors limiting reproduction. Sex ratio data from 48 samples of eight species suggest that: (a) the extent of host or egg limit ation in a species varies between site collected and time of year; and (b) on average, species are at an intermediate position on the egg/host limitat ion continuum, with a bias towards host limitation.