Researchers at the International Crops Research Institute for the Semi-arid Tropics (ISRISAT) in Hyderabad find Indian farmers obtain lower groundnut yields than African farmers, due to pest damage. Indian farmers spray their crops at least seven times in a season, making it impossible for the prey species to recolonise the crop as quickly as the pests. African farmers rarely use chemical sprays. (Pesticide News, No 16)

When farmers destroy jassids and thrips -- two pests that cause superficial damage -- they also destroy parasites of the leaf miner, the next major pest to appear. On withholding sprays, researchers found 70-80 per cent of the miners were parasitised causing less damage to the groundnut crop.

Later in the season the armyworm attacks the leaves and though it may eat 50 per cent of the leaves, there is little effect on the yield. When the Heliothis or pod borer attacks at the end of the season, there are no insect enemies left to protect the crop. Successive spraying of insecticides kills them all