Susceptibility of the Boll Weevil (Coleoptera: Curculionidae) to Methyl Parathion in Nicaragua

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Abstract
From 1982 through 1984, the relative toxicity of methyl parathion to various populations of the boll weevil, Anthonomus grandis grandis Boheman, from the León and Chinandega regions of Nicaragua, was assessed by topical application. The weevil populations at two locations exhibited a pattern of increasing susceptibility to methyl parathion as the cotton season progressed, with LC50’s ranging ca. 10-fold (0.14–1.52 μg per weevil and 0.09–0.79 μg per weevil, respectively). Early-season exposure of these populations to methyl parathion–treated trap crops may explain this seasonal pattern of response. These results differ from results of other regional studies with respect to magnitude of the LC50’s of methyl parathion and seasonal pattern of response. Nicaraguan populations of the boll weevil appear to be significantly more resistant to methyl parathion than other populations previously studied. Relatively resistant boll weevil populations may, in part, explain the historical tendency toward use of higher doses of methyl parathion for boll weevil control in Nicaragua compared with the southern United States.