Cocoons of diapausing and nondiapausingBathyplectes curculionis(Thomson) were treated with carbofuran, methoxychlor, methyl parathion, Imidan® and radioactive carbofuran to determine if cocoons were susceptible to insecticide penetration. Cocoons of diapausing individuals were impervious to all materials and dosages tested. Cocoons of nondiapausing individuals did not inhibit penetration of lethal dosages of any compound or dosage used. Our data indicate that insecticides may cause significant mortality of nondiapausingB. curculionisin the field.