Temperature threshold for growth and temperature-dependent weight gain of field-collected Tipula Montana (Diptera: Tipulidae)
Tipula montana, an upland tipulid of northern Britain and generally considered a montane species, was collected from the northern heath habitat of Waskerley Common, County Durham. The growth rate of larvae of Tipula montana was monitored at temperatures ranging from 1°C to 15°C at long photoperiod of 18 h light and 6 h dark. There was no significant growth at 5°C. At 7°C and above, the growth rate increased significantly in larvae initially in instars II and m. However, the growth rate of larvae initially in instar TV was unaffected by temperature, probably due to nearing the onset of pupation. 7°C is the minimum mean monthly temperature found during the main growing season (May-September) at Waskerley Common. Temperature had no significant effect on the weight at which moults to subsequent instars occurred but did accelerate the larval development.
At Waskerley Common T. montana follows either a one- or two-year life-cycle. If adequate temperatures (i.e. > 7°C) are not maintained during the growing season, fluctuations could occur in the numbers of individuals following the two life-cycles, resulting in varying numbers of adults produced at each emergence.