Influence of egg load and host size on host‐feeding behaviour of the parasitoid Aphytis lingnanensis

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Abstract
Direct behavioural assays were used to investigate the influences of host size and parasitoid egg load on the decision to host feed versus oviposit made by the parasitoid Aphytis lingnanensis Compere. Egg load was manipulated without concurrent influences on the history of host contact by exploiting size‐related variation in fecundity and by holding parasitoids at different temperatures to vary the rate of oocyte maturation. Host feeding comprised a series of feeding bouts, separated by renewed probing of the scale insect body. Successive feeding bouts were progressively shorter, suggesting that hosts represent ‘patches’ yielding resources at a decelerating rate. Parasitoids were significantly more likely to host feed on smaller hosts and oviposit on larger hosts. Neither egg load nor the treatment variables (parasitoid size and holding temperature) exerted significant influences on the decision to host feed versus oviposit on second instar (low quality) hosts. The failure to observe an effect of egg load on host‐feeding decisions was not simply a reflection of the parasitoids being entirely insensitive to egg load; significant effects of egg load on parasitoid search intensity and clutch size decisions were observed. Parasitoids developing on second instar (low quality) hosts experienced high levels of mortality late during development and yielded very small adults. The discord between these experimental results and predictions regarding the importance of egg load underscores the need for additional work on the proximate basis for host‐feeding decisions and the nutritional ecology of insect parasitoids.