Eggload dynamics and oviposition rate in a wild population of a parasitic wasp

1. This paper develops and tests in the field a model that predicts the ovi position rate and the rate of egg maturation of a synovigenic parasitic was p during a foraging period. The parasitoid is Aphytis melinus, the highly s uccessful biological control agent of California redscale (Aondiniella aura ntii), a pest of citrus worldwide. 2. Females were sampled in the interior canopy of grapefruit trees either j ust before and at the end of the foraging period over 2 days and were disse cted to determine the starting and ending eggload distributions. A group of females was caught before the onset of activity and kept in vials in the f ield in trees with honey but without access to hosts during the foraging pe riod. Their eggload at the end of the day was used to estimate the egg matu ration rate during the foraging period. 3. Two stochastic models are used to predict the eggload distribution at th e end of the day. Both use the observed starting eggload distribution, the observed length of the foraging period and the estimated rate of egg matura tion. The model providing the better fit uses an oviposition rate which is an increasing function of the eggload. 4. The eggload does not attain a steady state distribution during a foragin g period. One-third to one-half of the population is predicted to experienc e egg-limitation at some time during the foraging period. Five percent of t he population will experience egg-limitation a second time within a single day. 5. The common occurrence of egg-limitation over a single day and the relati vely high rate of change of states between egg- and time-limitation imply t hat the rate of nutrient acquisition and use are likely to be subject to st rong evolutionary pressures.