Phoresy and parasitism: water mite larvae of the genus Arrenurus (Acari: Hydrachnidia) on Odonata from Lake Binowskie (NW Poland)

Larvae of the genus Arrenurus parasitize Odonata, Diptera and Coleoptera. This work describes relationships between Arrenurus larvae and Odonata (imagines, larvae and exuviae) in a Polish lake. The mites examined were found on 2349 adult odonates (277 female and 872 male), 80S larvae (356 female and 449 male) and 395 exuviae of 34 species from Lake Binowskie and its vicinity. In total, 1128 larval water mites were collected from adult odonates, 556 from larvae, and 165 from exuviae. Water mite larvae were found on imagines of 9 species, on larvae of 12 species, and on exuviae of 9 species. Among adult of odonates only damselflies (Zygoptera) were parasitized, and a high prevalence (up to 77.8%) and intensity (up to 195 parasites per host) of parasitism were recorded. Adult females were more frequently infested than males, the preferred body parts being the thorax and the ventral side of the middle segments of the abdomen. Both phoretic and parasitic larvae of water mites were found on odonate larvae. Phoretic larvae constituted 25.8% of the total number of water mite larvae on odonate larvae. The occurrence of water mite larvae on exuviae shows their mortality when mites fail to move onto the eclosing adult odonate or when mites do not get detached from odonate larvae before their emergence from water.