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

1. The immature stages of the craneflies Lipsothrixnigrilinea and L. fenderi are spent in galleries within decayed red alder(Alnus rubra), in low order streams of the Pacific Northwest. L. fenderialso occurs in some coniferous wood and wood in semi-terrestrial sites atstream margins. Larvae of both species feed on the wood and areimportant degraders of this material.
The immature stages are briefly described and behaviour of the twospecies is compared.
L. nigrilinea has a predominantly biennial life cycle. It emergesfrom April to August in response to receding water level. The absenceof 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 andadult weights.
L. fenderi is basically a biennial species, with a more synchronizedautumn emergence. A portion of the population may emerge after 1year if oviposition occurs early enough to allow autumnal growth oflarvae or if growth is relatively rapid.
The extended life cycle of Lipsothrix spp. and the broad emergenceof L. nigrilinea are concluded to be adaptations to a habitat/resourcewhich is relatively stable and allows long-term association.