Biological studies on a number of Moorland Tipulidae

Abstract

The life-history and ecology of Tipula subnodicornis Zetterstedt have been studied on the Moor House National Nature Reserve, an area of upland blanket-bog with an altitude range of 1300-278oft (396-845m). The annual life-cycle is maintained under different temperature conditions by adaptive responses to temperature and photoperiod during development. The optimum temperature for growth and the magnitude of response in growth rate to change in temperature both decrease during larval development. The growth phase is followed by an overwintering stage which is probably temperature independent but cannot be considered as a diapause as the metabolic rate does not drop. This phase can be ended by subjecting the larvae to an increased day length (l8hr). In the field the increasing day length in spring synchronises pupation. In the autumn emerging species, T. pagana, which has a summer diapause, decrease in day length breaks the diapause and promotes development towards pupation. In this case it has been shown that the degree of synchronisation is directly related to the shortness of day length. The population dynamics of T. subnodicornis have been studied and it was shown, by the method of k factor analysis, that overwinter mortality in the field is density dependent. Experimental manipulation of density in enclosures in the field and in culture indicated that the same was true for the early instars. A multi variate analysis on the factors affecting wing length, which was used as an indication of size and fecundity, showed that site and year were the most important influences in both sexes and that the effect of density was significant for the males. Wing length was not significantly correlated with altitude in either sex.