Functional shifts in the use of parasitized host by a tephritid fly: The role of host quality

Superparasitism a phenomenon in which parasitic insects lay eggs in already-exploited hosts, provides a useful context in which to examine the dynamics of parental investment. This study explored conditions under which female Mediterranean fruit flies (Cerati capitata) shift from avoiding superparasitism of hot fruit to preferring it, even placing eggs directly into existing egg laying. An a prior hypothesis of costs and benefits was use to predict how to use and avoidance of parasitized fruit would change in response to changes in fruit size and ripeness. We predicted that avoidance would decrease with increasing fruit size, while use would increase with decreasing ripeness. Using a field-cage assay, ripeness was held constant and the size host coffee berries manipulated. Avoidance of parasitized berries was significantly less pronounced on large berries than on small ones. In a second experiment, size was held constant and ripeness manipulated. On unripe berries, females deposited the majority of clutches directly into existing egg-laying cavities. On ripe berries, by contrast, the same female deposited most clutches in previously unparasitized fruit. Parallel in the patterns in the frequency of female-female contests were observed, supporting the notion that a fruit's value is determined by an interaction between fruit size or ripeness, on one hand the prior occurrence of egg, on the other. Laboratory assays suggested that use of exiting site had-advantages inn terms of time savings; female behavior thus constitute a relatively uncommon example of adaptive superparasitism in which parasitized hosts are actually preferred over unparasitized ones.