THE BEHAVIOR OF ARRENURUS LARVAE (ACARI, HYDRACHNIDEA) PARASITIZING DIPTERA

In order to parasitize an adultfly, larval water mites must be pulled through the surface film of the water by the fly as it emerges from th e pupal skin. The arousal response of Arrenurus rotundus Marshall on p upae of two ceratopogonid flies, Palpomyia slossonae (Coquillett) and Sphaeromias longipennis (Loew.) is variable and contagious so that the probability of arousing in time to grasp the ecdysing fly increases w ith number of mites on a pupa. In contrast, interference among larvae in large groups reduces the chances of larvae transferring from the pu pa to a fly Many larvae fail because these opposing density dependent responses reduce the number of mites per fly to a level that does not kill hosts prematurely. Arrenurus larvae attacking Odonata show a very different set of traits because they do not have to penetrate the sur face film of the water, and have minutes, rather than seconds, to sele ctively attach to hosts that can support hundreds, rather than tens of larval mites.