Mites (Water mites) Unranked Hydracarina
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Common names: Water mites
Water mites are arachnids with four pairs of legs (at least as adults). Mites have only one main body segment. Freshwater species are good swimmers which is made possible by the presence of swimming hairs on their legs.
Some feed on organic mater while some are parasitic and attach themselves to other invertebrates, like the damselfly in the photo below.
Ectoparasitic water mites are important parasites of aerial stages of aquatic insects. Their larvae parasitise semi-aquatic hosts and must detach while the host is in a suitable habitat for reproduction of parasite and host. Adult mites detach during tandem oviposition by the host. Detachment occurs only at a height up to 10 mm above water.
A female Xanthocnemis zealandica carring water mites. See text below photo.
Scientists Jose Andres and Adolfo Cordero of the Universidade de Vigo, Pontevedra, Spain, took a close look at parasitism in their research “Effect of Water Mites on the Damselfly, Ceriagrion tenellum,” published in a 2002 edition of Ecological Entomology.
They pointed out:
1. "Water mite parasitism is expected to have an important effect on damselfly survivorship and reproductive success, because mites drain considerable amounts of body fluids from their hosts," they wrote in their abstract. "This study tests the effect of water mite parasitism in a marked population of the damselfly Ceriagrion tenellum during 1995 (individuals marked as mature adults) and 1996 (individuals marked as tenerals)."
2. "Almost all teneral individuals were parasitiszed (98%) and mites were aggregated strongly on some individuals. Parasite load increased during the season."
3. "Parasites had no effect on the probability of recapture of hosts as mature adults. The average daily survival rate of lightly- and heavily-parasitised individuals, estimated with Jolly's stochastic method, did not differ significantly."
4. "In 1995 parasites had a significant effect on host mating success. The probability of mating was about 25% lower for heavily parasitised males than for lightly parasitized males. Lightly parasitized males also mated more times than heavily parasitized males, even if heavily parasitised males lived longer. In 1996, parasitism did not have an effect on male mating success. In both years mites had no effect on female lifetime mating success."
In conclusion, they found that "water mite parasitism does not reduce damselfly survivorship, but it could reduce male mating success in some circumstances. Further long-term studies are needed, especially in populations with a lower incidence of parasitism."