Relative Toxicity of Five Organophosphorus Mosquito Larvicides to Mallard Ducks

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Abstract
The toxicity and potential field hazards of 5 mosquito larvicides to mallard ducks were investigated through laboratory and field-enclosure studies. The insecticides tested, parathion, Baytex, Sumithion, Guthion, and SD-7438, are either in use or are considered for use in mosquito suppression programs in California. Laboratory tests showed that parathion and Baytex were highly toxic to ducks in acute doses, while Sumithion, Guthion, and SD-7438, in that order, manifested decreasing acute toxicity. Chronic feeding trials varying from 5 to 9 weeks were conducted with the 5 insecticides at 25 ppm in diet, and also with parathion and Baytex at 5 ppm in diet. Ducks given diets contaminated with 25 ppm Sumithion, Guthion, and SD-7438, and 5 ppm parathion and Baytex showed no definite reaction to their exposure. Birds on 25 ppm parathion and Baytex in diets were repelled by their diets, lost considerable weight, and ultimately some died. Surviving birds recovered rapidly after they were placed on noncontaminated diets. Small experimental ponds containing pinioned mallards were sprayed six times at biweekly intervals with 0.4 lb/acre of the insecticides. Birds were not sprayed directly, were fed noncontaminated feed, and maintained on ponds for 6 months after treatments. Toxicity trials in the laboratory indicated a potential hazard of Baytex and parathion to mallards, but ducks showed no apparent effects of exposure to any of the insecticides in pond trials.

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