This is the first report of parasite infestation of Tipulidae by water mite larvae in the middle reaches of a river in Japan. Forty-four species of adult crane flies were identified. The most abundant species was Antocha (Antocha) bifida ALEXANDER 1924 with 22 204 individuals (76.5% were male). Some 2113 individuals (9.5%) were parasitized by water mites, viz., Sperchon plumifer THOR 1902 (maximum: 40/host, mean value: 3.5 ± 2.5/host). 73.1% of S. plumifer larvae were attached to the abdomen. Many S. plumifer larvae parasitized A. bifida adults from late May to early July, but after a small flood, few S. plumifer larvae were collected. Floods have a major impact on both the A. bifida population and on its parasite, the S. plumifer larval population.
IntroductionThe hydrachnellid water mite species pass through an ectoparasitic larval stage on insect hosts of various orders (reviewed by SMITH and OLIVER, 1976). Recently, studies on many aspects of the host-parasite relationships (from genes to communities) between aquatic insect adults and larvae of water mites have been reported (PROCTOR, 2004). In contrast, in Japan, such reports concerning the host-parasite relationship are very rare. Although IMAMURA (1950), andMITCHELL (1967) reported on water mites parasitic on damselfly and stonefly, little is known about the host-parasite relationship between water mite larvae and aquatic insect adults. In addition, these studies have focused on small streams or upper reaches of rivers.Crane flies, one of the largest groups of aquatic insects, occur in most types of freshwater habitats such as springs, streams and seepage areas, rivers, lakes, ponds, marshes and temporary pools (reviewed by ROGERS, 1933). They have been particularly successful in subdividing resources within these habitats (reviewed by PRITCHARD, 1983). Many studies of the seasonal abundance and growth rates of crane flies in relation to environmental factors (water temperature, dissolved oxygen concentration, and food abundance) have been conducted in lentic/lotic habitats LIVINGSTON and GELHAUS, 1993;PRITCHARD, 1983;WINTERBOURN, 1996). However, there have been few previous reports on the seasonal changes in emerging adult crane flies in the rivers of Japan, and the parasite infestation of adult crane flies by water mite larvae has either been overlooked, or no rele-
