LD50 and LD90 values were determined by bioassay of topical and stomach poison applications for lindane, fenitrothion and permethrin. At equivalent dosage rates fenitrothion was generally the most and permethrin the least, effective. Permethrin and fenitrothion were more toxic as contact poisons whereas lindane was more effective as a stomach poison. Using LD50 and LD90 values and sucrose treated tissue paper as a substrate, the persistence of three insecticides as stomach poison was determined at various temperature regimes with light excluded. Both lindane dosages had a short persistence (3 - 7 days) at 5°C and 15°C; fenitrothion had a similar persistence at 15°C and a moderate persistence at 5°C (LD50 for 7 - 14 days and LD90 for 14 days) but permethrin retained its toxicity for at least 21 days at 5°C, 15°C and 30°C. No additional degradation was obtained at 5°C with a continuous light intensity of 2415.6 lux for any of the insecticides and permethrin retained its toxicity for at least 56 days. Persistence of fenitrothion (LD90) and permethrin (LD50) were evaluated on wheat, privet and Brussels sprout plants growing under the same light and temperature regimes referred to above. The plants had no effect on the persistence of fenitrothion. Permethrin retained its toxicity for more than 40 days but slightly higher levels of activity were retained on wheat than on the other two plants. Rain fastness on growing plants was only evaluated for permethrin; there was little loss in wheat, a greater loss on privet and Brussels sprouts.
|Date of Award||1979|