The feeding ecology of certain larvae in the genus tipula (Tipulidae, Diptera), with special reference to their utilisation of Bryophytes

Abstract

Bryophytes are rarely used as a food source by any animal species, but the genus Tipula (Diptera, Tipulidae) contains some of the few insect species able to feed, and complete their life-cycle, on bryophytes. Vegetation particle volumes ingested by larvae of eleven Tipula species increased only marginally between instars and not to the extent expected from the rate of growth of body mass. Early and late instars within a species frequently ingested similar sized particles. The overall efficiency of digestion of vegetation particles was low and similar between the four instars of each of the eleven species. Generally, the only method by which later larval instars can obtain a higher proportion of nutrients is by feeding on a larger number of smaller vegetation particles and not by ingesting large particles. In feeding choice experiments, Tipula confusa preferred moss species from woodland habitats, whereas Tipula subnodicornis did not show an overall preference for either woodland or moorland moss species. Tipula subnodicornis also showed a less extensive hierachical preference/avoidance than Tipula confusa for the ten moss species investigated. The moss species Campylopus paradoxus and Sphagnum papillosum accumulated Pb(^2+) ions and Zn(^2+) ions to high concentrations. There was some evidence that Tipula subnodicornis larvae were deterred from feeding on these mosses with high levels of introduced heavy metal ions. Tipula montana was able to thrive and complete its life-cycle in Britain at lower altitudes than had been previously thought. Individuals of this species show a combination of one-year and two-year life-cycles at Waskerley Common. The feeding methods employed by Tipula species can explain why some of them have remained as consumers of bryophytes.