AN American way of killing vegetable-leaf-eating insects by fooling them with a 'sexy' odour is to be imported to Hong Kong. Highly regarded, cheap and environmentally friendly, the 'fatal attraction' trick requires a basin of water and a dose of pheromone, according to agricultural officials. Pheromone is a chemical substance released by animals to attract the opposite sex. Man-made pheromone costs about $10 a dose. Put the items in a field and the harmful, male caterpillars of the diamondback moth are lured to the water and drown themselves. 'Count the number of caterpillars and you may have a rough idea of the numbers of moths and the eggs they have laid in the field,' agricultural officer Wendy Ko told 50 farmers at a seminar yesterday. The caterpillar's favourite vegetables include Chinese cabbage, broccoli, watercress, and choi sum. Last year 12,300 tonnes of watercress, worth $33 million, were produced on farms here. Free samples of pheromone were distributed to farmers and Ms Ko said the method had proved effective and popular in the US. Agriculture and Fisheries Department senior crop development officer Fong Chun-wah said: 'The method can save farmers much trouble in determining how much or when pesticide should be applied.' The method targets diamondback moths, or plutella xylostella, whose caterpillars destroy leaves and are a serious pest in southern China. An average Hong Kong vegetable farm would require five doses of pheromone, each of which is effective for two months.