FNZ 2 - Osoriinae (Insecta: Coleoptera: Staphylinidae) - Ecology
McColl, HP 1982. Osoriinae (Insecta: Coleoptera: Staphylinidae). Fauna of New Zealand 2, 96 pages.
( ISSN 0111-5383 (print), ; no. 02. ISBN 0-477-06688-7 (print), ). Published 23 Dec 1982
Until recently little attention has been given to the habitat requirements of osoriine beetles. Smith et al. (1978) studied the ecology of Osorius planifrons Le Conte, which they found in large numbers beneath a golf green in Arizona. Moore & Legner (1974) indicate sandy margins of streams, rotting wood, and leaf litter as habitats for North American osoriines, and Smith et al. (1979) quote other sources as having found them "beneath stones and logs in damp places" and in accumulations of organic debris in the crowns of broomsedge in coastal South Carolina.
In New Zealand, osoriines exploit the litter, fermentation, and humus horizons beneath indigenous vegetation, usually evergreen forests of various kinds, though some species have been found under subalpine and alpine vegetation, and they have been recorded from rotting logs, moss, and, rarely, fungi on the forest floor. I found one species in organic debris in an epiphyte garden about 8 m from ground level. Occasionally they have been recorded from humus or rotting logs beneath Pinus radiata (McColl 1974).
Organic horizons beneath forests provide a stable environment with little risk of food shortage or exposure to climatic extremes (McColl 1975). Smith et al. (1978, 1979) regard the presence of organic detritus and high soil moisture as vital requirements for survival of O. planifrons. In New Zealand most species ingest detritus both as adults and larvae, and their mouthparts are suitably adapted for this purpose, with stout mandibles for gathering organic matter into the buccal area. Smith et al. (1979), however, regard the similar-shaped mandibles of O. planifrons, which they found to ingest organic detritus, as being adapted to push aside the soil to assist their passage through it. They further suggest that the long, slender setae on the prementum, mentum, and gula of O. planifrons (which are also present in Nototrochus and Paratrochus) are analogous to the ammochaetae of fossorial ants, which are used for carrying particles of sand or soil. I am unable to confirm this for New Zealand osoriines because I have not closely observed their burrowing behaviour. The New Zealand osoriines further lack the enlarged fossorial protibia of Osorius spp. Their habitat consists of loosely packed organic detritus rather than soil, so such modifications are probably unnecessary, since it can be easily pushed aside.
Smith et al. (1978, 1979) consider the main food source for O. planifrons to be "microbes" present in organic debris, and the failure of this beetle to survive in autoclaved soil supports this. However, McColl et al. (1980) found that numbers of bacteria were higher in the beetles' faecal material than in habitat litter, and were highest in the gut, which suggests a large, active bacterial fauna within the gut. Numbers of Actinomycetes and fungi were smaller in the gut than in habitat litter or faecal material, which suggests that Paratrochus may be feeding on these micro-organisms. Low numbers of actinomycetes and fungi in the gut of Paratrochus may also indicate selective feeding against them, however.
The absence of commensal protozoans in the gut of O. planifrons was thought by Smith et al. (1979) to preclude utilisation of cellulose-rich substrates by this beetle. McColl et al. (1979) found three Bacillus strains in the gut of Paratrochus that were able to digest the hemicellulose xylan, and that none of the Bacillus strains isolated from habitat litter had this ability. High levels of protease activity were recorded from the gut, indicating production of this enzyme both by the beetle and by symbiotic bacteria in the gut. Organisms isolated from the gut were generally better able to utilise gelatin, citrate, glucose, mannitol, sucrose, melibiose, and amygdalin, to synthesise ß-galactosidase and oxidase, and to reduce nitrates than organisms from habitat litter or faecal material.
The complex digestive processes and the food sources of these detritus-ingesting beetles require further study.