EGG LOAD AND THE DECISION TO HOST-FEED IN THE PARASITOID, APHYTIS-MELINUS

1. We make and test predictions about how the number of eggs a female parasitoid is carrying (her 'egg load) influences her propensity for ' host-feeding', the consumption of host body fluids. 2. We first develo p a simple dynamic state variable model that predicts that parasitoids should host-feed only when completely empty of eggs. This result refl ects an important assumption of the simple model, namely the absence o f a delay between host-feeding and the maturation of eggs. 3. We there fore develop two additional models that incorporate a delay by adding extra 'pre-egg' state variables to the simple model. Adding even a sho rt delay makes possible a non-zero threshold egg number at and below w hich the parasitoid host-feeds. 4. We then compare the results of the models with behavioural observations of host-feeding by Aphytis melinu s DeBach (Hymenoptera: Aphelinidae). 5. As predicted by the models wit h an egg-maturation delay, host-feeding was associated with low, but n on-zero egg loads. Aphytis host-fed at egg numbers ranging from 0 to 5 (mean: 2.0). 6. There was no clear single threshold egg number at hos t-feeding; the fraction of Aphytis host-feeding declined monotonically with increasing egg loads.