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
Mite
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.
Mite
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.
Lesion
Sperchon mite on adult Simlium female
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.
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
Mites
Mermithids