Conclusions:

1. Parasitic mites (Acari: Hydrachnidia) on Pupae and Adults of Simuliidae (Insecta: Diptera) Alfons Renz1), Reinhard Gerecke2), Peter Martin3) 1) Alfons.Renz@uni-tuebingen.de; 2) Reinhard.Gerecke@uni-tuebingen.de; 3) PMartin@zoologie.uni-kiel.de Abstract Larvae of various species of water mites (Hydrachnidia) are known to parasite on adult blackflies. Typically, the larvae of these mites are located inside the pupal cocoons of Simuliidae, where they wait until the imago hatches. They then attach to the emerging adult fly, engorge by feeding on the hosts haemolymph, and profit from its upstream movement to compensate for downstream drift and thus repopulate seasonally fast-flowing breeding sites. Sperchon larva on Simulium pupa Observations In 2003 and again in 2004, we observed extraordinarily high prevalences of Sperchon cf. setiger in some streams around Tübingen in Southern Germany. In the parasitized populations of Simulium equinum, S. ornatum and S. latipes, prevalence rates were high, reaching 80 to 90 % in over 100 pupae examined, and the average number of larvae was 3-5 mites per Simulium pupa, with a typical negative-binomial distribution pattern. Mites were seen crawling avidly over and into the pupae cocoons, but were not attracted by Simulium larvae, even when these were situated close to the pupae. Only one mite was seen on a female adult fly, hatched in an emerging cage. A distinctive melanization marked the site, where the mite had previously fed. Mite larvae of different sizes were seen on the pupae, indicating that some mites were actually feeding and might therefore develop to nymphal or even adult stages, without passing through a phoretic stage on the emerging adult fly. Mite Mite Lesion Sperchon mite on adult Simlium female Conclusions: Though Sperchon mites are generally considered being mainly phoretic parasites, their number and the fact, that they may also suck haemolymph, makes them potential regulators of Simulium population. Levels of infestation seem be linked to water pollution and were lowest in rivers with little organic load. Like mermithid nematodes, phoretic mites take advantage of the upstream compensatory flight of Simulium adult female flies. Sperchon spec. larva Compensation of downstream drift by phoretic parasites of Simulium adult flies MitesMermithids