New techniques for controlling pests

Press, 14 January 1982, Page 12

New techniques for controlling pests

From

“The Economist,”

London

Science Spot •

Biological pesticides will not supersede conventional pesticides, but the two used together promise more effective and safer ways of protecting crops. Such integrated pestmanagement schemes are already being used in Holland and parts of America and Switzerland. In the canton of Geneva, 35 per cent of fruit orchards are combining biological and traditional agents — and often saving money. For these farmers, synthetic pesticides cost twice as much as an integrated management package (if labour costs are included). The saving represents only a small fraction (Uz percent) of the income derived from the crop itself, but is welcome enough. Perhaps the most popular biological agents today are the pheromones, communication chemicals released by insects. Sex pheromones, for instance, are “mating calls" released by female insects to attract males. As pesticides, they can be used simply to confuse would-be mates. But they show more promise used as monitoring devices or as lures. Knowing precisely when to apply pesticides to a crop can be very important. This is so with the moths whose larvae attack peas. Only the larvae themselves — not the moths — are vulnerable to today's insecticides, and the larvae are exposed for just a few hours before burrowing into peas.

Dr Clive Wall of Rothamsted Experimental Station in Hertfordshire. Britain, can now predict hatching times to an accuracy of a day by luring male moths into sex-phero-mone-scented traps and counting them. This tells the farmer when the male moth population is on the increase, heralding the moths’ peak mating period. So the farmer can predict quite accurately when the larvae will appear and spray at the critical time. Less pesticide is used with greater efficiency.

Dr Wall has also shown that only minute quantities of the pheromone are needed to attract the male pea-moth. The surrounding vegetation in the vicinity of the concentrated pheromone source can absorb the pheromone and release adequate doses slowly from the

surface of its leaves. In his work Dr Walls is collaborating with a small Hertfordshire firm, called Oecos. Other insects being monitored with sex pheromones include the cotton pest called the pink bollworm. Sex pheromones for the male bollworm are already available from Albany International, New York. They should be available soon from Palo-Alto-based Zoecon, which recently established a joint venture with drugrelease company Key Pharmaceutical of Miami. There are also tricks that combine biological agents. Dr Windle Burkholder at the University of Wisconsin has devised a sex-pheromone trap for the Trogerma beetle, a pest that attacks dry cereals. The pest has especially nasty habits that can be turned against it. The beetles rush into the pheromone-baited sex trap. There they encounter a parasite fatal to the beetle. The disappointed bugs return to the community and die. Then their cannioalist young feed off the adult carcasses, to become infected with the parasite in turn.

Nor are sex pheromones the only useful ones. Dr Burkholder is also working with socalled aggregatory pheromones, chemicals which attract both males and females. The pheromones can lead them to a site whicn can be poisoned (this work is being carried out with Albany International). So far, aggregatory pheromones have been used on three different bark-beetles, includ-

ing those that cause Dutch-elm’ disease. A two-year field trial was completed last year in Scandinavia using aggregatory pheromones in conjunction with pesticides against the elm beetle, with satisfactory results. The pheromones in the trial were in part supplied by the Norwegian firm Bbrregaard. Other pheromones being investigated include: • The alarm pheromone for aphids (greenfly). Normally aphids lie stationary below leaf surfaces, protected against conventional pesticide spraying. When the aphids sense the alarm pheromone, however, they move around and come into contact with the pesticide. • Recognition pheromones of the fire ant, a domestic pest. When this chemical is in the air, worker ants rush back to their nest. Dr Jim Tumlinson of the agricultural research station in Florida has found that these ants can be persuaded to carry toxic chemicals back to the nest. • Pheromones that

discourage egg laying by white cabbage moths. Dr Cees Persoons of the official Dutch research organisation has .shown that the female moth will not lay her eggs on valuable crops when this pheromone scent is around. Pheromones are not confined to insects. Similar chemical signals have been identified in vermin, such as rats, and in rabbits. Integrated pest management may well become a feature of control for higher animals too.