RED MITE IMMUNE TO INSECTICIDES

Press, Volume XCIX, Issue 29177, 11 April 1960, Page 23

RED MITE IMMUNE TO INSECTICIDES

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AUCKLAND.’ April 10. The tiny red mite—one of the again. The cause of much damage to foliage and of scarring to fruit, the mite has developed such resistance to the commonly used phosphorus insecticides that spraying is now useless in many major fruit-producing ?r Orchardists have suspected this for some time, and confirmation has just been given by Dr. R. A Harrison, entomologist at the Plant Disee sew Division of the Department of Scientific find fodustrial Research atafisn* Afoert For more than a year; Dr. Harrison has been dosing individual mites weighing about one fiftythousandth ot an ounce with minute quantities of poisons The Veiults are startling, and a serious blow to orchardists. Resistant mites need doses M 0 or

more times stronger than normal mites do to kill them—doses so powerful that they are completely impracticable for spraying. Eff ecto Of »AX The whole situation had apparently cropped 'up through the defensive use of D.D.T. to control codlin moth, said Dr. Harriaon- -

enemies) had thrived and their nunfoers and nativity had increased ngtftr un® brought under coatNt by the phosphorus torays. “Now it aotaM that if they are resistant to one type of phosphorus spray? they are resistant to the lot* Dr. Harrison aaid. “It’s a bad thing from the grower's petal of view, as it cuts out such a lot of useful sprays.” The answer seemed to be a return to earlier methode kiTling the mttaa during the dormant period with agricultural oils, or using .wvfcidm to Mil the eggs, he said. This would have to be done early in the season, however, aa there now appeared to be no eeoeomical way of killing the aduM mites. “However, there is a good posrfbfflty that research in the next year or two will stress the importance of using highly specific insecticides for the control of codlin moth and teefroUera, so that orchardists may not need to use chemicals at all for nite con- > trol," Dr. Harrison said. The seme thing seemed to be . happening with leafrollers, which attacked apple trees in Nelson orchards. They were now showing some resistance to the normal method ef control; by DDD„ a relative of DD.T. Investigations were being made at Mount Albert into thia, and thft diwiaddw amtui method of control would be de-

veloped before the resistance got as far aa immunity, aa it had done in the caee of the mites and hae happened with hove flfee,“ aaM Dr. Harrison. “Tritay they are 280 to 800 ttmeo aa resistant to DD.T. aa they were when It was first Introduced. About the only thine they haven’t built up some coaldance to is the pyrothrum jftaip of chemicals, as used In foe household aeroools."