Background information

Natural enemies

There are several basic texts on biological control which give background information on different types of biological control, biological control agents and successes of biological control (e.g. (van den Bosch et al. 1982, DeBach and Rosen 1991, van Driesche and Bellows 1996).

Natural enemies of invertebrate pests

Predators: these simply consume their prey, and they are often not very specific in their choice of prey species, although there are exceptions. Predators commonly used for biological control are Coccinellidae (ladybirds) for control of aphids, and predatory mites to control pest mites. Predators are capable of killing large numbers of individual pests.
Parasitoids: these usually develop on a single host, and because of the complex relationship between parasitoid and host, they tend to be more host-specific than predators. Ectoparasitoids feed externally on the host, and endoparasitoids develop internally within the tissues of the host. Ectoparasitoids often paralyse the host before depositing an egg, and the developing larva feeds on the tissues of the host. Endoparasitoids can develop on one or more stages of the host including the egg, larval stages, pupa and adult.
Pathogens: these include viruses, bacteria, fungi, protozoa. Nematodes are also often included as pathogens in this context. These microorganisms cause disease in their hosts, and have most often been used for inundative augmentation biological control rather than classical biological control.

Natural enemies of weeds

Phytophagous insects and mites have been used extensively for weed biological control, but plant pathogens have also been used. Weed biological control agents can target seeds, foliage, stems or roots of the weed, and combinations of agents attacking different parts of the plant are often employed. Biological control can reduce plant vigour so that other controls are more effective in integrated weed management systems.

References

DeBach P. and Rosen D. (1991). Biological control by natural enemies. Cambridge University Press, Cambridge, UK.

van den Bosch, R., Messenger, P.S. and Gutierrez, A.P. (1982). An introduction to biological control. Intext Educational Publishers, Plenum Press, New York and London. Pp 247

van Driesche R.G. and Bellows T.S. (1996). Biological control. Chapman and Hall, New York. 539 pp.