Larvae of a vast majority of water mite species are parasites of aquatic insects. Owing to this, they migrate to new localities, and are able to survive unfavourable environmental conditions. This also concerns species from subgenus Arrenurus s. str., parasites of dragonflies. The detailed analysis of this phenomenon, however, has only been possible in the last several years, since the key to the identification of larvae from genus Arrenurus Dug. was published. In 2010, the parasitism of Arrenurus s. str. larvae on dragonflies in the Lake Świdwie reserve (NW Poland) was analysed. Larvae of 9 species of water mites were recorded on 107 imagines of dragonflies from 8 species. The following were identified as hosts of water mites for the first time: Anax imperator, Libellula quadrimaculata, and Leucorrhinia caudalis. The highest prevalence occurred in the case of: Erythromma najas and Lestes dryas (100%), Coenagrion pulchellum (96.5%), and C. puella (80.0%). Coenagrion pulchellum was infested by 9 species of parasites, C. puella by 6, and Erythromma najas and Lestes dryas by three species. The highest number of host species occurred in the case of Arrenurus maculator (5); followed by A. cuspidator, A. batillifer cf., A. bicuspidator, and A. tetracyphus (3 each); A. papillator, A. tricuspidator, and A. bruzelii (2 each), and A. claviger (1). Differentiation of preferences of particular parasites towards various parts of the host body was observed, probably related to the coevolution of parasites and hosts, and competition between the host species. The body sizes of the parasites suggest that approximately 50% of body size growth of water mites from subgenus Arrenurus s. str. occurs at the stage of parasitic larva.
The relationships between water mite larvae parasitizing Coenagrion scitulum in core and edge populations were described. A total of 636 larvae of 7 water mite species were found on 143 C. scitulum adults (82 females and 61 males). C. scitulum was recorded for the first time as a host species for Arrenurus cuspidator, A. bruzelii, A. bicuspidator, A. tricuspidator, A. claviger and Hydryphantes octoporus. The degree of infestation by particular parasite species was typical for these species. In contrast, the parasites’ preferences for host body parts were not typical, as they preferred abdominal segments 2–4, which in earlier studies had been avoided by water mite larvae. No differences were found in degree of infestation of Coenagrion scitulum individuals between core and edge populations, with the exception of Hydryphantes octoporus, which parasitized damselflies only in core populations.
Many aquatic insect species, including aquatic Hemiptera, are parasitized by water mite larvae. Although this situation may cause damaging impacts to the hosts, the mites can disperse and colonize new localities in this way. Little is known about the frequency of water mite ectoparasitism amongst the aquatic Hemiptera in Turkey. In this study, larval water mite parasitism on aquatic Hemiptera, which have been collected from different localities in Turkish Thrace, was evaluated. It was found that only nine individuals, belonging two different species in a total of 367 hemipteran specimens, were parasitized by larval water mites. Furthermore, variations in sizes and shapes of the mites on the waterscorpion Ranatra linearis Linne, 1758 and Nepa cinerea Linne, 1758 were determined. These are the first records for larval mite parasitism on R. linearis and N. cinerea in Turkish Thrace.
During the studies on ecology of Trichoptera of anthropogenic water bodies we have unexpectedly discovered the parasitic larvae of water mites of the species Tiphys torris on the pupa of Triaenodes bicolor. This is the first documented case of the parasitism of water mites on the caddisfly pupa as well as the first ever record of the species which is regarded as a dipteran parasite on caddisflies. The situation is very untypical for preimaginal stages of caddisflies are used by phoretic and not parasitic water mite larvae. Parasitism has been confirmed in this case by the formation of stylostomes and enlarged sizes of the bodies of the larvae. This is probably the case of facultative parasitism in which the pupa has served as a substitute of the adult form of a caddisfly.