LD 50 values of methyl parathion and endrin to tobacco budworms and bollworms collected in the Americas and hypothesis on the spread of resistance in these lepidopterans to these insecticides.

Abstract

Tobacco budworms, Heliothis virescens (F.), collected in 1970 from cotton in the Mante-Tampico area of Tamaulipas, Mexico, and at Brownsville, Texas, were resistant to methyl parathion; those from Mississippi, southern and western Mexico, and South America were susceptible. The LD50values (mg/g after 48 hours) in the area of Waco Texas, were higher in 1970 than in 1969. Bollworms, H. zea (Boddie), collected in 1970 from cotton or tobacco in Central America and from one location in southern Mexico, were more resistant than those collected in northern Mexico, the United States, and South America.