The Biology of Tipula subnodicornis Zetterstedt, with Comparative Observations on Tipula paludosa Meigen

Abstract

A study under field conditions of 2 species of crane flies which occurred commonly on the Moor House Nature Reserve, Westmorland, an area of high moorland situated on the Pennines. Tipula subnodicornis had a marked diurnal emergence period while T. paludosa emerged over a short period immediately after sun-set. Both species emerged with ripe eggs and mating, then egg laying, followed emergence. Egg laying was rapid in both species and the majority of eggs were laid within the first day. Both species had a well-defined emergence period and the middle two-thirds of T subnodicornis population emerged in 11 days. A capture-recapture study on T subnodicornis showed that the males lived longer than the females, although both had a high daily mortality rate and this accounted for the apparent greater number of males observed in the field. The eggs of T subnodicornis were laid deeper than those of T paludosa but in both species the majority of the eggs were laid within 2cm of the soil surface. Larvae of T paludosa were found only on mineral soils while those of T subnodicornis were restricted to the peat moor. Final instar larvae of T. subnodicornis were found on a wide range of vegetation types and densities of over 100 larvae/m2 were found on Juncus squarrosus and Ercophorum vaginatum moor. A population study on T subnodicornis showed that there was normally a high mortality in the egg and first 2 instars. Under the very dry conditions in 1955, the larvae did not survive to reach the second instar on several vegetation types. However wet Sphagnum flushes, which normally maintain only a small population of larvae, did not dry out completely during this dry weather and these were available to re-populate extensive areas of the moorland. It is stressed that favorable climatic conditions are necessary during the early stages of the species in order that a population similar to or greater than the preceding one can be produced.