ECTOPARASITES AND MATING SUCCESS OF MALE ENALLAGMA EBRIUM DAMSELFLIES (ODONATA, COENAGRIONIDAE)

Several researchers have found inverse relationships between mating success of males and degree of parasitism. Whether such mating biases result from female choice of parasite-resistant males as mates, or from parasite-mediated reductions in male competitiveness for access to females, has stimulated considerable discussion. I found that single male damselflies, Enallagma ebrium (Hagen) (Odonata: Coenagrionidae), were significantly and consistently parasitized by more larval water mites (Arrenurus spp. and Limnochares americana Lundblad) than were males caught either in tandem or copula with females. In contrast, male size was inconsistently related to short-term mating success, although there was a consistent negative correlation between male size and mite numbers which was statistically significant on 2 of 7 sampling days. The existence of such natural covariation and its possible effect on male mating success has not been widely discussed. Lastly, I found that heavily-parasitized males responded less often to the presence of male models, and took significantly more foraging trips, than did lightly-parasitized males. Short-term mating biases with respect to ectoparasitism for E. ebrium males appears to result from reductions in competitiveness of heavily-parasitized males for access to females. Furthermore, my results strongly suggest that apparent reductions in competitiveness reflect decisions by heavily-parasitized males to pursue mating tactics which are energetically inexpensive.