By Jürg Bürgi

In contrast to the widely reviled "chemical cudgel" used by the agro-industry, the "green cudgel" - biological pest control - receives the highest praise when it involves eliminating vermin and weeds in a targeted and environmentally friendly way while maintaining biological diversity.

No one had anything against South American parasitoids being imported to Africa to exterminate the mealybug; everyone kept quiet when the poisonous American cane toad was imported to Australia to eradicate pests in sugarcane fields; and when the thistle-eating Eurasian flower head weevil Rhinocillus conicus was about to be used in the United States, the protesters stayed at home.

While the first example above is rightly regarded as a tremendous success story, which brought Hans R. Herren, the director of the program concerned, the World Food Prize, the second unintentionally led to the spread of a species that is now wreaking havoc in an alien ecosystem as a dangerous pest in its own right. And the third example proved to be a danger to many rare thistle species in regions not used for agriculture. Unfortunately, these are not isolated cases.

Even Herren criticizes the fact that in the past, "sloppy work was sometimes done". The way in which pest control programs, and the preceding scientific investigations of the side effects, were geared to the interests of agriculture proved to be particularly dangerous for the environment and for species diversity. Once they had been released, the beneficial species concentrated on their intended task only in very exceptional cases. Usually, they searched for fodder outside the fields assigned to them, and several spread into ecosystems unable to cope with their aggressiveness and voracity.

In 1963, for example, fish farmers for the first time imported grass carp from Asia to the United States in order to control rampant water plants. It soon became clear that although the fish were indeed attacking the plants as a sideline, their favorite preoccupation was attacking a whole series of other creatures. The predatory land snail Euglandina rosea may be recalled as a particularly serious example of this type of mistake.

Imported from Florida and Central America to the Pacific island of Mooréa in the 1970s, it was meant to fight the African giant snail that had been introduced to the island previously. Instead of concentrating on the slimy and voracious pest, the cannibalistic newcomer annihilated seven domestic snail species instead, and probably wiped out a species of Partula snail that was found only on that island.

Particularly in the Third World, where small-scale farmers cannot afford spray control or have too little training to be able to use it correctly, the use of biological methods is regarded as the first choice for pest control. But things are by no means that simple, as was shown by the first world conference on the unwanted ecological effects of biological pest control, held in Montpellier in November 1999.¹

Although the scientists quickly agreed that research on unwanted effects when using beneficial species had to be decisively intensified, no consensus was reached on the extent of the efforts needed or on the rules to be observed in the process. Researchers from the United States and Europe were prepared to accept tighter restrictions than people working in hunger-threatened Africa.

For example, Peter Neuenschwander, the Swiss director of the International Institute for Tropical Agriculture in Benin, was willing to admit that precautionary measures are advisable. Where it was a matter of food security and minimizing crop losses, however, he demanded that evaluations should also take into account the consequences of doing nothing, as well as the damage caused by using pest sprays:

The method of biological pest control must not be squeezed out of the market by expensive and unrealistically strict conditions. ... The legal framework must not be designed in such a cumbersome way that biological pest control ceases to be an affordable method and is replaced by alternatives that are much more damaging to the environment. ... When assessing the risk and advantages, we must evaluate not only the ecological costs and benefits, but also the social and economic ones.

It is surprising how much these arguments, put forward by a representative of biological pest control, resemble those used by his biotechnologically oriented colleagues when defending themselves against regulations that restrict research. There are also other points in common: scientists are debating the use of genetically modified pathogens for biological pest control. Using this type of microorganism would represent a special challenge, one paper claimed. Because "there would be a danger of indirect effects that would be difficult to predict." As in classic biological pest control - using natural enemies - it is equally true in this field that "the effects may be irreversible."

All those who advocate unlimited use of the methods of biological pest control because it uses natural techniques but who reject biotechnology because of its imponderable risks must be given pause for thought by observations such as these. Both methods intervene in highly complex systems, neither can be reversed, both are under the same pressure to produce successes and avoid side effects, and both are unable to dodge the growing demand for expensive controls and prior testing. It is therefore hard to understand why the two methods should not be allowed to exist alongside each other, competing to outdo each other's results.

Jürg Bürgi is a freelance journalist from Basle.

¹ See E. Wajnberg, J.K. Scott, and P.C. Quimby (eds.), Evaluating Indirect Ecological Effects of Biological Control, Wallingford, Oxon, U.K.: CABI Publishing, 2001.