The biology and life cycles of Lipsothrix spp. (Diptera: Tipulidae) inhabiting wood in Western Oregon streams

Abstract

SUMMARY. 1. The immature stages of the craneflies Lipsothrix nigrilinea and L. fenderi are spent in galleries within decayed red alder (Atntts rtibra), in low order streams of the Pacific Northwest. L. fenderi also occurs in some coniferous wood and wood in semi‐terrestrial sites at stream margins. Larvae of both species feed on the wood and are important degraders of this material.2. The immature stages are briefly described and behaviour of the two species is compared.3. L. nigrilinea has a predominantly biennial life cycle. It emerges from April to August in response to receding water level. The absence of this cue results in an extension of the life span to 3 or more years. The non‐deterministic life cycle results in high variability of juvenile and adult weights.4. L. fenderi is basically a biennial species, with a more synchronized autumn emergence. A portion of the population may emerge after 1 year if oviposition occurs early enough to allow autumnal growth of larvae or if growth is relatively rapid.5. The extended life cycle of Lipsothrix spp. and the broad emergence of L. nigrilinea are concluded to be adaptations to a habitat/resource which is relatively stable and allows long‐term association.