Abstract
Little research has been done on egg diapause and the embryonic development of water mites. The aim of this study was to check the impact of temperature and periods of light on hatching of larvae of Eylais extendens. Three batches of eggs which were spawned on 30 July were placed at one of three temperatures (4, 10 and 20 °C) and two periods of light (7 and 14 h per day). Egg hatching (both, percentage of hatched larvae and rate of hatching) was found to differ between 4 versus 10 °C and between 4 versus 20 °C, but not between 10 versus 20 °C. The periods of light had no influence on hatching. This synchronization of hatching, enabling the eggs to emerge from diapause in the spring, could be considered an evolutionary adaptation aimed at postponing hatching of late-spawned eggs until a time allowing for completion of the full development cycle, including the parasitic larval stage.
Highlights
Little research has been done on the embryonic development of water mites and the impact of environmental parameters on hatching time and numbers
Our results confirm the existence of egg diapause in E. extendens, a standing-water species—egg diapause and delay of larval hatching has previously been reported for lotic species (Gerecke 2002; Martin 2010)
The results clearly indicate temperature as the factor stimulating hatching of E. extendens larvae
Summary
Little research has been done on the embryonic development of water mites and the impact of environmental parameters on hatching time and numbers. Most research was involved with the number of eggs spawned and the hatching time specific to particular species of water mites and the environmental determinants of these processes Water mites of the genera Hydrovolzia, Piersigia, Hydryphantes, Limnochares, Eylais and Hydrachna parasitize Heteroptera and Coleoptera (Smith and Olivier 1976). Eylais and Hydrachna are the only two genera that parasitize both Heteroptera and Coleoptera; these water mites have the longest parasitic period, which allows them to survive in the parasitic larval stage in unfavourable environmental conditions, including the winter (Nielsen and Davids 1975; Zawal 2002, 2003a). Species of the genus Eylais may hibernate in the form of eggs; this applies in particular to E. extendens and E. infundibulifera (Nielsen and Davids 1975)
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