Foraging Behavior of Aphytis Melinus: Effects of Patch Density and Host Size

Abstract

The influence of size and density of the California red scale (Aonidiella aurantii) on the behavior of the parasitoid Aphytis melinus was examined. Aphytis appears to employ a simple strategy of searching the same amount of time in patches of different host density, and as a result the same fraction of hosts was encountered at all host densities. Only the first few of the encountered hosts were actually parasitized, however, probably due to egg depletion. Different instars of the California red scale yielded Aphytis progeny of different size and sex ratios. Small hosts, such as the second instar, produced small Aphytis with a male—biased sex ratio. The third instar, a larger host, produced much larger Aphytis and a more balanced sex ratio. Perhaps because of its low quality, the second instar was parasitized at a lower rate than the third instar, in both the field and laboratory. Parasitism on second instars in the field was lower when third instars were abundant. Host size distribution may have significant effects on Aphytis size and sex ratio, with implications for biological control of the red scale.