Biological studies on some moorland short-palped craneflies (Tipulidae, Diptera)

Abstract

Moorland Tipulidae (in particular, short-palped craneflies with special reference to Tricyphona immaculata) have been studied on the upper Teesdale moor district of Chapel Fell (Ref NY 863349) between September 1992 and August 1993. The lifecycles of a number of short and long-palped craneflies were recorded using a series of pit-fall traps located at fourteen sites previously selected to represent the range of vegetation present at Chapel Fell summit, 630m.Spiracular disc size was measured in five small-palped species and frequency distribution histograms are given showing the presence of four instars in each. Using pit-fall traps Tricyphona immaculata was found to emerge as an adult both in May and September. Through the collection of peat from the field and subsequent extraction of larvae Tricyphona immaculata was found to exist in two groups, one beginning its lifecycle in the spring, the other in the autumn. Laboratory experiments on eggs of Tricyphona immaculata revealed that eggs do not respond differently to long and short- day photoperiod regimes and that egg development was positively related to temperature. Field experiments indicated species-site habitat associations. Larval densities for short- palped species are given along with adult-site occurrence for both long and short-palped species. The two different habitats of Sphagnum and Nardus are shown to maintain different densities of three species of short-palped cranefly. Annual variation in cranefly numbers is discussed in relation to the summer drought of 1992 after which most species showed a decline in number. Egg development in Tipula czezeki was found not to be influenced by short and long-day photoperiod regimes and this finding is compared to the hatching distribution found in Tipula pagana eggs when subjected to similar conditions. A comparative assessment on larval growth showed that the relationship of breadth and length differs between the species studied. Molophilus after and Ormosia pseudosimilis adults are also compared physically.