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Background information

Environmental risks of biological control

The environmental risk of pesticide use was forcefully publicised by Rachel Carson in her book Silent Spring (Carson 1963). This landmark publication signalled a turning point, particularly in the USA, when public pressure to reduce the amount of pesticides used on crops, as well as the development of increasing levels of pesticide resistance, and promotion of the philosophy of sustainable agricultural practices, resulted in public outcry and the demand for alternatives to pesticides. Biological control became one of the obvious choices and Ehler (1990) quoted some of the world's most prestigious biological control researchers, who gave the following assurances about the safety of biological control:
" adverse effects on the ecosystem occur from biological control" (DeBach 1974);
"...research in this sphere [biological control] results in prodigious economic benefits - without any environmental hazards..." (Simmonds and Bennett 1977);
"The use of predators and parasites for pest control, when it is the result of a well thought out, carefully executed program, is in our opinion, risk-free" (Caltagirone and Huffaker 1980).

However, when considering biological and chemical control methods, it is clear that in comparison with the latter, biological control is irreversible, self-perpetuating and self-dispersing. These attributes are, of course, amongst the benefits of biological control as a component of sustainable pest management programmes, but they are also the factors which have alerted researchers to the potential environmental implications of such introductions.

Assurances regarding the environmental safety of biological control were questioned (e.g. (Howarth 1983, Howarth 1991, Samways 1994, Simberloff and Stiling 1996), and for a few years views became highly polarised, particularly in the USA. Biological control practitioners became very defensive, claiming that the 'conservationists' had no evidence for negative impacts of biological control (e.g. (Howarth and Ramsay 1991, Hopper 1995, Strand and Obrycki 1996 pointed out that the lack of evidence for negative environmental impacts of biological control introductions is a result more of the lack of study of effects than the absence of these impacts. Lockwood (1993) argued that the pitfalls of biological control were the non-target effects, possibly leading to species extinction, the high failure rate of biological control programmes and the inability to explain failure. He attributed some of these consequences to the lack of adequate legislative requirements for quarantine and post-release studies for biological control agents for insect pests. In recent years, however, more funding has become available for research into non-target impacts of biological control, and researchers have taken the opportunity to conduct good ecological research in this area to the benefit of environmentally safer biological control.

Safe use of biological control can lead to enormous economic and environmental benefits and regulation must take into account the risk of rejecting potentially useful species by over-cautious decisions.


Caltagirone L.E. and Huffaker C.B. (1980). Benefits and risks of using predators and parasites for controlling pests. Ecological Bulletin 31: 103-109.

Carson R. (1963). Silent Spring. Hamish Hamilton, London.

DeBach P. (1974). Biological control by natural enemies. Cambridge University Press, London.

Ehler L.E. (1990). Environmental impact of introduced biological control agents: implications for agricultural biotechnology. Pp. 85-96 In: Risk assessment in agricultural biotechnology, J.J. Marois and G. Breuning (Ed.) California Division of Agriculture and Natural Resources, Oakland.

Hopper K.R. (1995). Potential impacts on threatened and endangered insect species in the United States from introductions of parasitic Hymenoptera for the control of insect pests. Pp. 64-74 In: Biological Control: Benefits and Risks, H.M.T. Hokkanen and J.M. Lynch (Ed.) Cambridge University Press, Cambridge, UK.

Howarth F.G. (1983). Classical biological control: panacea or Pandora's box. Proceedings of the Hawaiian Entomological Society 24: 239-244.

Howarth F.G. (1991). Environmental impacts of classical biological control. Annual Review of Entomology 36: 489-509.

Howarth F.G. and Ramsay G.W. (1991). The conservation of island insects and their habitats. Pp. 71-107 In: The Conservation of Insects and their Habitat, N.M. Collins and J.A. Thomas (Ed.) Academic Press, London.

Lockwood J.A. (1993). Environmental issues involved in biological control of rangeland grasshoppers (Orthoptera: Acrididae) with exotic agents. Environmental Entomology 22: 504-518.

Samways M.J. (1994). Insect Conservation Biology. Chapman & Hall, London. 358 pp.

Simberloff D. and Stiling P. (1996). How risky is biological control? Ecology 77: 1965-1974.

Simmonds F.J. and Bennett F.D. (1977). Biological control of agricultural pests. Pp. 464-472 In: Proc. 15th International Congress of Entomology.

Strand M.R. and Obrycki J.J. (1996). Host specificity of insect parasitoids and predators. BioScience 46: 422-429.