Entomologist Reviews Insect Control Work

Press, Volume XCVI, Issue 28399, 4 October 1957, Page 16

Entomologist Reviews Insect Control Work

“Up until the end of the nineteenth century the entomologist was regarded as little more than a curiosity hunter,”.said Mr Alan D. Lowe of the Entomology Division, Department of Scientific and Industrial Research, at Ashburton. He was* speaking at the monthly meeting of the Canterbury branch of the Royal Society of New Zealand. “Pasteur and other men of his time began, through investigations of life cycles and feeding habits, the work of economic entomology,” he said. As early as 2600 B.C. the impact of insects on the activities of man had been realised and drawings had been found of silkworms and honey bees, said Mr Lowe. There had been no recognition, however, of the carrying of disease by insects. The causes of widespread epidemics, of bubonic plague transmitted to man by the rat flea, and the carrying of typhus by the body louse were not known. Insect populations ’ reached enormous numbers, said Mr Lowe. With the grass grub infestations in the Ashburton county he had estimated that if there were only 25 grubs to the cubic foot—this would be a low estimate—and if only a quarter of the county was infected, then there would

be some 200,000 million grubs present. In a 40-acre field at Darfield infested with cabbage aphis, there had been about 1000 aphids on each plant—about 40,000 million an acre. To assist in his work, Mr Lowe has invented a “bug counter,” an instrument built in Christchurch, which electronically counts aphids passed in a stream of water through a glass tube. Air transport had increased the danger of insects entering New Zealand and mosquitoes found on aircraft had survived a flight at more than 20,000 feet from the tropics, said Mr Lowe. Control of insects employed physics, chemistry, biology and statistics, said Mr Lowe. It was necessary to know the insect’s life cycle, its feeding habits, the lethal dosage of the insecticide to be employed and the calculation of when the most favourable time for attacking it would occur. The simplest form of control was that of nature, and could be seen whenever seagulls followed a plough seeking and eating the grass grubs, said Mr Lowe. Plants could be bred to be resistant to or rather tolerant of the pest involved.

Parasites could be imported to deal with insects as had been done in California, where Australian ladybirds had been used to combat aphis infestations. Chemical methods of control had progressed from the early use of lead arsenate and nicotine to the spectacular successes of D.D.T., 8.H.C., dieldrin, and Aldrin. D.D.T. had combated typhus outbreaks in Italy in 1944, and recently an application of only two ounces of aldrin to the acre had halted a locust plague in the Middle East, said Mr Lowe. The need now arose for insecticides that were selective, said Mr Lowe. Treating of raspberry canes with D.D.T. killing the aphis, but also destroyed all the ladybirds, and a plague of red spider infested the canes.

Mr Lowe emphasised the danger of indiscriminate use of chemicals without full knowledge of all the factors involved. “Resistant insects can be bred from the survivors of a near-lethal dose," he said.

While D.D.T. applications to the soil to counter grass grub did not harm young plants, it had been demonstrated that chemicals such as B.H.C. and lindane exerted a definite inhibition of seed growth, especially in wheat, he said.