The survival of insects may depend on adaptations toward seasonal change in abiotic factors such as weather and temperature. Those adaptations, which may be controlled by both environmental and genetic factors, may include hibernation of adults (VAN NERUM BUELENS 1997), resting eggs (BRADFORD ROFF 1997), or an endogenously controlled and determined dormancy. Such condition is known as diapause and includes, for example, developmental arrest and reduced oxygen consumption on larval or pupal stage (TOKESHI 1995, HAND PODRABSKY 2000, DING et al. 2003). Lakes may be considered rather stable compared to terrestrial environments, where insects may face conditions such as drought and subzero temperatures. Despite this, annual changes in a lake environment can be dramatic. Ice-cover prevents both water mixing, due to wind and wave effects, and oxygen transfer between the lake and the atmosphere; snow-covered ice prevents light from reaching benthic primary producers. Lake temperature under the ice can be close to 0℃ while temperature near the bottom may be higher, due to heat release from the sediment, resulting in increased water density (OLAFSSON 1979). This usually leads to stratification of ice-covered lakes, where little or no benthic primary production occurs. At the same time, benthic microbial activity may consume oxygen from the sediment and water above, causing an oxygen-depleted layer of water above the sediment that may affect the whole lake. During anoxic conditions, sulphides, toxic to most organisms, may form (HAGER-MAN 1998). Most of the winter scenarios mentioned apply to Lake Myvatn in northeast Iceland (OLAFSSON 1979, THORBERGSDOTTIR et al. 2004).
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