Life history and feeding role of the xylophagous aquatic beetle, Lara avara LeConte (Dryopoidea:Elmidae) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dn39x521q

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  • The purpose of this study was to document the life history of the xylophagous elmid beetle, Lara avara. and to estimate its contribution to wood degradation in Oregon streams. Field collections, mark-recapture, and laboratory rearing were used to determine details of the life cycle. Laboratory feeding studies and field population estimates were used to estimate fecal production by natural populations of Lara larvae. The life cycle was found to be four to seven years long, with all but two to three months of that spent in the larval stage. Adults live approximately three weeks, and occur from May to August. Female adults lay 100 - 150 eggs on submerged wood. Larvae grow through seven instars, taking about one year for instars one to three, and from three to six years for instars four to seven. Last-instar larvae leave the water in the spring, and burrow into moss at the edge of the stream. Pupation occurs when the moss dries in early summer. The pupal stage lasts at least two weeks. I found Lara to have a mean abundance of 34 mg/m² stream bed, or 57 mg/kg wood, in the Coast Range streams that I sampled. Variation in abundance was not related to variation in size or density (mg/cm³, an index of decay) of the wood used by Lara as habitat. Lara larvae probably obtain nutrition from decaying wood by absorbing substances that have been liberated by fungal exoenzymes, and by digesting and absorbing the contents of fungal and bacterial cells. Lara larvae do not produce their own cellulase, nor do they have a symbiotic gut flora similar to that of xylophagous craneflies. Assimilation efficiency is probably less than 10%. Fecal production of Lara larvae averaged 9% of their body weight per day in laboratory culture. When extrapolated to field population levels, this corresponds to a fecal production of 1.1 gm/m²/yr in Coast Range streams.
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