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

Abstract

SUMMARY. This study documents the life history of the xylophagous elmid beetle, Lara avara, and estimates its contribution to wood degradation in Oregon streams. The life cycle was found to be 4 to 6 or more years long, with all but 2–3 months of that spent in the larval stage. Larvae grow through seven instars, taking about 1 year for instars 1–3, and from 3 to 5 or more years for instars 4–7. Last‐instar larvae leave the water to pupate. Adults live approximately 3 weeks and occur from May to August. The eggs are deposited on submerged wood. Larvae probably obtain their nutrition by absorbing substances liberated into decaying wood by microbial activity. They do not produce their own cellulase, nor do they have a symbiotic gut flora similar to that of xylophagous cranefly (Tipulidae) larvae. Faecal production by L. avara larvae averaged 13% dry body wt d‐1. This yields an estimate of faecal production of 1.6 g m‐2 y‐1 in Oregon Coast Range streams (about 0.3% y‐1 of wood standing crop).

Wood biofilm as a food resource for stream detritivores

“…The high assimilation efficiencies of epixylon (26-36%) by the three detritivores were unexpected. Steedman and Anderson (1985) reported assimilation efficiencies of 4-7% for L. avara fed wood, efficiencies that were much lower than what we found. Wood consumed by L. avara was highly grooved, indicating that individuals had ingested primarily wood (Steedman and Anderson 1985).…”

“…In contrast, wood is considered to be a poor-quality food resource (Anderson and Cummins 1979). In the only published study of wood assimilation by aquatic insects, Steedman and Anderson (1985) measured assimilation efficiencies of 4-7% for Lara avara, a slowgrowing beetle species, fed alder and conifer wood. Golladay and Sinsabaugh (1991) suggested that wood biofilms (epixylon) might be overlooked sites of metabolic activity in streams.…”

Coarse woody debris in temperate littoral zones: implications for biodiversity, food webs and lake management

“…Epixylic fungi and bacteria derive certain amounts of N and P directly from wood (Tank & Dodds, 2003), whereas algae benefit from carbon released during degradation of wooden tissue . Nutrients liberated from CWD can also be directly used by epixylic invertebrates, including facultative xylophages Steedman & Anderson, 1985;Harmon et al, 1986); however, invertebrate consumers are mostly subsidized by biomass produced by epixylic biofilm. Some experiments have shown that wood biofilm was readily assimilated by consumers, and its abundance (particularly in terms of algae) was negatively correlated with invertebrate numbers Eggert & Wallace, 2007).…”

“…The ecology of xylophages is poorly recognized and their contribution to CWD degradation was examined only in streams. According to previous studies, xylophages use their own enzymes to digest wooden tissue or they use for this purpose sequestered fungal enzymes or symbiotic bacteria and protozoans inhabiting their guts (Anderson et al, 1984;Steedman & Anderson, 1985;.…”

Mouthparts, gut contents, and retreat-construction by the wood-dwelling larvae of Lype phaeopa (Trichoptera: Psychomyiidae)

“…The complete larval development of aquatic insects associated with submerged wood is reported for the dipterans Lipsothrix spp. Loew, 1879 (Dudley & Anderson, 1987) and Xylotopus par (Coquillett, 1905) (Kaufman & King, 1987), the coleopterans Macronychus glabratus Say, 1825 (Phillips, 1997) and Lara avara LeConte, 1852 (Steedman & Anderson, 1985), the tropical ephemeropterans Povilla adusta Navas, 1912 and Asthenopus spp. Eaton, 1871 (Sattler, 1967;Tobias, 1996), and the trichopteran Lasiocephala basalis (Kolenati, 1848) (Hoffmann, 2000).…”