EDWARDS, D.D.: Does Host Sex Enhance the Transmission Dynamics Of Parasites? A Study of Mites and Midges

Larvae of the water mite Unionicola foili undergo a brief parasitic phase with adult chironomids during their life cycle and in doing so acquire nutrition and a mechanism for dispersal. An examination of several life history characteristics of larval U. foili parasitic on Chironomus tentans revealed no significant difference in the number of larvae infesting male and female midges. Similarity in the distribution of larvae among male and female hosts appears to be counterproductive, given that only females return to water during oviposition. Mite larvae infesting female chironomids were more likely to return to water when females deposited egg masses. Furthermore, there was a significant correlation between egg deposition and the detachment of larval mites from female hosts. These data suggest that oviposition may play an important role in ensuring that larvae re-enter the aquatic habitat following a parasitic phase with female midges. Interestingly, larval U. foili infesting male chironomids were more likely to return to water than expected due to chance, and a comparison of the frequency with which larvae returned to water when parasitizing male and female chironomids indicated no significant difference between these treatment conditions. The mechanism responsible for increasing the likelihood that larvae parasitizing male chironomids return to a watery environment remains unclear. Future studies will address the possibility of parasite-mediated changes in host behavior.