Observations on reproduction, development, and sexual behaviour of stream-inhabiting water mites (Acari: Hydrachnidia)

Abstract

Details of reproduction, development, and sexual behaviour are known only for a few water mite species, mostly from standing water. This study reports laboratory observations on 20 species from two small streams in North Germany. Ovigerous females carried between 1.4 (Aturus fontinalis) to 69 eggs (Sperchon setiger). In most species, eggs were laid consecutively in distinct clutches, generally with <50 eggs per clutch. Separately deposited single eggs were exclu- sively found in containers housing the small species Feltria rouxi, Ljania bipapillata, and A. fontinalis. Lifetime repro- duction was recorded for Sperchonopsis verrucosa (110 eggs in 3 years) and Sperchon thienemanni (122 eggs in 2 years). Development from egg until larval hatching took 2-10 weeks, eggs laid late in the year took up to 3 months. The deutonymphal stage generally takes several months, depending on food supply. The period between the immo- bile deutonymph and adult emergence takes 1-4 weeks. In the laboratory, life spans vary from several months (male F. rouxi, A. fontinalis) up to 3 years (female S. verrucosa, Lebertia glabra). In most cases, spermatophore deposition occurs even in the physical absence of females. For stream-living species in temperate climates, different patterns of overwintering are known: hibernation often occurs as adult. Overwintering exclusively as deutonymph has never been observed, but part of the population often hibernates at this stage. In species with parasitic larvae late in the year (Wettina podagrica, L. glabra and Sperchon squamosus), most specimens probably hibernate at the deutonymphal stage. Overwintering as a well-developed larva remaining within the clutch envelope has been observed only in Atractides nodipalpis. Hibernation at the egg stage is known from the literature for Sperchon glandulosus.