The behavioural decisions of insect parasitoids have been the subject of dynamic state variable models, which explicitly incorporate the physiological state of the parasitoid, e.g. her age and 'egg load' (number of mature eggs). Such models have been most recently applied to parasitoid 'host feeding', the consumption of host body fluids or tissues by the adult female wasp. The models developed to date, and recent empirical work with Aphytis melinus, have highlighted the importance of the physiology associated with host feeding to the behavioural decision whether to host feed or oviposit. Below, I develop a new dynamic state variable model which incorporates the physiological features associated with host feeding in Aphytis. My intention is to make qualitative predictions about the effects of various physiological featues on host-feeding behaviour and to make quantitative predictions about the relationship between egg load and host feeding in Aphytis.