EGG LIMITATION IN PARASITOIDS - A REVIEW OF THE EVIDENCE AND A CASE-STUDY

Life history theory predicts that a nontrivial proportion of parasitoi ds should exhaust their egg supply during their lifetime. We reviewed the literature on egg limitation in parasitoids and found partial supp ort for this prediction. Most of the evidence in support of egg limita tion is indirect and does not constitute absolute proof of egg limitat ion. However, a few direct studies in which field-collected parasitoid s were dissected, gave unequivocal evidence of egg limitation. Egg lim itation was detected both in proovigenic species, in which it signals the attainment of maximum fecundity, and in synovigenic species, where it is more likely to be temporary than permanent. We demonstrated sub stantial egg limitation in the synovigenic parasitoid Aphytis aonidiae . Although an unknown (and probably large) proportion of egg-limited i ndividuals was apparently unable to mature eggs for unknown reasons, t he egg load distribution indicated that even those individuals able to mature eggs could be at risk of becoming egg limited. Thus, egg limit ation in this species can apparently occur through egg depletion or an inability to mature eggs. We investigated possible correlations betwe en time of day time of gear, ambient temperature, parasitoid size, and host density on egg limitation in A, aonidiae. We found a slight tend ency for egg load to drop during the course of the day. Although we co uld detect no effect of time of year or of temperature on egg load, la rger parasitoids had higher egg loads than did smaller ones. Finally, we could detect no effect of host density on egg load. This result is paradoxical given recent theory predicting increased egg limitation wi th increased host availability We suggest that already-documented stat e-dependent behavior in A. aonidiae may partly explain this unexpected result. Parasitoids may reduce the risk of egg limitation when the ho st encounter rate is high by exhibiting increasingly selective host-us e patterns with declining egg load. (C) 1998 Academic Press.