THE VALUE OF THE ORGANIC PHOSPHORUS INSECTICIDES MALATHION AND DIAZINON FOR THE PROTECTION OF SHEEP AGAINST BODY STRIKE.1

Abstract

SummaryThe efficiency of the organic phosphorus insecticides, malathion and diazinon, in protecting sheep against body‐strike by Lucilia cuprina, under semi‐field conditions, was evaluated in comparison with aldrin, dieldrin and BHC.The insecticides were applied by jetting to that area of the sheep on which the majority of body‐strikes originate, namely a strip about 12 inches wide from just in front of the withers to the butt of the tail. Care was always taken to saturate the wool down to the skin.Efficiency was measured weekly by placing 2–300 freshly hatched blow‐fly larvae on the skin of the treated portion of the experimental animals and checking survival rates 24 hours later. A treatment was considered to have lost its efficiency when larvae survived for 24 hours on two separate occasions on 50 per cent. of the sheep.Malathion at concentrations of 0.05 per cent., 0.1 per cent. and 0.25 per cent. was efficient for 7, 8 to 9 and 10 weeks respectively. Aldrin and dieldrin at the same concentrations were efficient for 11 to 18 weeks.In one experiment diazinon at a concentration of 0.008 per cent. was effective for 23 weeks and at 0.04 per cent. for 33 weeks whereas aldrin at 0.05 per cent. lost its efficiency after 9 weeks. In a second experiment performed during a period of high summer rainfall (35.56 inches in 18 weeks) diazinon at 0.02 per cent. gave protection for only 16–18 weeks and dieldrin at 0.025 per cent. for 7–9 weeks. In this experiment no difference in the efficiency of either insecticide could be detected in sheep with wool 3/4 to inches, 1 3/4 to 2 inches or 2 1/2 to 3 inches in length.The results showed that a concentration of not less than 0.02 per cent. diazinon would probably be necessary under field conditions to prevent body‐strike for long periods during which high rainfall occurs.