The cotton bollworm, Heliothis armiger is a very important cotton pest in Australia. It has a long history of insecticide resistance in Australia, to DDT in the early 1970's and to the pyrethroids in 1983,.In 1976, entomologists from the New South Wales Department of Agriculture at Tamworth began a nation wide resistance monitoring program for H. armiger. Each year Heliothis, collected mainly from New South Wales and Queensland cotton sites, are sent to the Tamworth Agricultural Research Centre for testing. The progeny from the moths in each sample are reared.in the laboratory on an artificial diet and are tested with insecticides when they reach 30-40 mg weight. Varying concentrations of insecticides dissolved in solvents, are tested against Heliothis by putting a I ul drop on each caterpillar back and count the number dead after 48 or 72.hours. Mortality is plotted against concentration and we calculate the.LD50 (the concentration required to kill 50% of the test group) and the slope of the line (a measure of the variation of response to the insecticide)..We test all insecticides which are used against H. armiger and those with potential for use.