Detritivores

Feeding on detritus, essentially the remains of dead animals and plants together with the microorganisms that bring about their decay, is a very old habit among Insecta, and most orders include some detritivorous species (Southwood, 1972). Detritus-feeding insects are especially significant in aquatic ecosystems where large quantities of dead plant matter may accumulate annually. In streams and rivers the source of this material is largely overhanging vegetation. In still waters the major contributor to detritus is phytoplankton, though in shallow areas emergent vegetation may make a significant contribution. In terrestrial ecosystems insects are generally unimportant as detritivores, this role falling predominantly to other arthropods, notably Collembola and oribatid mites. Two notable exceptions are termites, the majority of which feed on wood litter, and the Australian Oecophoridae and Tortricidae (Lepidoptera) many of whose larvae feed on eucalyptus litter (Common, 1980). The foliage of eucalyptus contains substantial amounts of phenolics (including tannins) and essential oils, rendering it unpalatable to many herbivores, and is also extremely deficient in nitrogen. Thus, the ability of these moth larvae to utilize this resource gives them a key role in energy flow and matter recycling in this specialized ecosystem.

According to Anderson and Cargill (1987), some 45% of an estimated 10,000 species of aquatic insects in North America ingest some detritus. The major groups of detritivores are in the orders Trichoptera, Diptera, Ephemeroptera, Plecoptera, and Coleoptera, and their eating habits may be categorized as shredding and gouging, scraping, filter feeding, and deposit collection (Figure 23.2). The shredders, gougers, and scrapers inevitably will ingest the living saprophytic microorganisms on the surface of the dead vegetation, as well as the plant tissue itself, and a key question is the relative importance of these as food. For some detritivores, there is evidence that the microorganisms provide all of the nutrients with the relatively indigestible plant tissue simply passing unchanged through the gut. In other species, dead plant tissues are the main source of energy though microorganisms may supply some essential components. Generally, only about 10% of the ingested material is assimilated, the rest being defecated. However, the breaking up of the material into smaller particles as it passes along the alimentary tract is in itself important, the increase in surface area facilitating microbial activity.

Detritus may vary considerably in its nutrient availability and in its content of feeding deterrents, and a major role of the microorganisms is to "condition" the material, for example, by softening the tissues, by chemically converting the contents into a form that can be used by the insects, and by detoxifying the deterrent compounds. The availability of detritus as food may also vary seasonally, typically becoming maximal in the fall following

702 leaf drop and the death of emergent vegetation and phytoplankton and again in spring as temperatures rise permitting renewed microbial activity. Thus, many detritivores (especially shredders) exhibit their greatest growth rates in the fall and early winter, before entering a phase of arrested development until spring.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook


Post a comment