Toxicity and persistence of effectiveness of somc organophosphorus insecticides against green aphid Aphis gossypii Glover on apple leaves

Abstract

Eight organophosphorus insecticides were tested in the laboratory for their intrinsic toxicity as deposits on apple leaves to third instar nymphs of Aphis gossypii Glover. Demeton- S-methyl, chlorfenvinphos and phosphamidon were highly toxic, dimetboate and phosalone were moderately toxic, and monocrotopbos, quinalphos. and melhamidophos were less toxic compounds. Persistence of effective toxicity of these insecticides at commercially recommended rates of application was examinted under field conditions on apple cv Red Delicious. Phosphamidon, dimethoatc and phosalone provided protection for more than three weeks following spray applications. Chlorfenvillphos gave protection for about 14 days, demeton- S-metbyl for 10 days and monocrotophos for 4 days. Quinalphos and metbamidophos were less persistent and effective.