Population Dynamics of Unionicola formosa (Acari: Unionicolidae), a Water Mite with a Harem

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Abstract
The population dynamics of the water mite Unionicola formosa, a symbiont of the freshwater mussel Anodonta imbecilis, were monitored for 2 years in a North Carolina [USA] farm pond. Since the density (number/mussel) of females was correlated with host-size, but males were uniformly isolated at 1/host, the sex ratio approached 80:1 (female:male) among large mussels. This "harem" distribution persisted throughout the year. Female mites were most abundant in winter and experienced .apprx. 50% mortality by early summer. Nymphs were present throughout the year. Size-frequency data for females, coupled with the pattern of occurrence of nymphs, suggested that recruitment into the adult population began in May as overwintering nymphs transformed to adults, and continued into late summer and autumn. Egg production occurred throughout the year, but oviposition and the development of eggs were seasonal, with larvae emerging from the host from late spring to early autumn. Adult U. formosa probably live at least 2 years.