Scientists have hit on a new way to combat one of Australia's worst pests -- create a male-only line. The eight millimetre-long Queensland fruit fly is so prevalent and adept at destroying crops it is threatening the nation's Aus$6.9 billion (US$6.2 billion) horticultural industry. Until recently, farmers used agri-chemicals to keep it at bay but after a long period of review the Australian Pesticides and Veterinary Medicines Authority recently restricted the use of insecticides. Australian scientists at the government-run Commonwealth Scientific and Industrial Research Organisation are now exploring how feeding certain genes to larvae can alter the DNA so the flies grow into sterilised males whether they start out as male or female. If the five-year study succeeds, thousands of the flies will be released into infected orchards across Australia to breed with female flies, which mate only once. "We believe that our sterile insect technology, through development of a male-only line of Q-fly, will offer a new environmentally friendly, sustainable and cost effective approach to assist in managing this damaging pest," said lead scientist Paul De Barro. Researchers also hope to create 1.5-millimetre sensors, which can be glued to the flies to pinpoint their location and identify where they breed, which has so far eluded them. "It will tell us how many sterile flies we will need to release and most importantly, when to release them," De Barro said. The Queensland fruit fly is considered one of farming's most damaging pests, infesting apples, avocados, capsicums, kiwi fruit and mangoes. Its larvae can rot and discolour fruit and vegetables.