Inactivation of deltamethrin on stored wheat

Residues of deltamethrin on wheat grain of 12% moisture content, stored in the laboratory at 25°C, remained constant within experimental error over a 15-month interval. However, the biological activity of the residues against Sitophilus oryzae (L.) declined to 78% of the initial value at 3 months, and to 65% at 15 months after application. Inactivation of a proportion of the intact residues is indicated.