Lethal Residues of Seven Insecticides for Control of Tarnished Plant Bug Determined by Four Methods1

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Abstract
Dimethoate was the best of 7 insecticides evaluated for control of Lygus lineolaris (Palisot de Beauvois) in apple orchards. The 4 methods employed for evaluation were consistent in ranking relative toxicities. The method that permitted contact with the deposit on an excised leaf was most practical for determining amounts of deposit needed for adequate control. Results were expressed in lethal concentrations (LC50 and LC95 g (AI/liter) and lethal residues (LR50, and LR95, μg/cm). With the direct spray method, LC95 values were 13.2, 5.3, 3.9, 1.2, 0.73, O.11, and 0.056 g (AI)/liter for DDT, phosalone, endosulfan, phosmet, tetrachlorvinphos, fenitrothion, and dimethoate, respectively. With the excised leaf method, LR95 values were 7.7, 5.7, 5.5, 0.77, 0.28, and 0.0085 μg/cm2 for DDT, endosulfan, phosmet, tetrachlorvinphos, dimethoate, and fenitrothion, respectively. DDT, the only insecticide recommended for control of the tarnished plant bug in Ontario until 1972, was found to be the least toxic of the insecticides tested.

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