Residual effects of deltamethrin and malathion on different populations of Sitophilus granarius (L.) on treated wheat grains

Deposits of deltamethrin and malathion up to 90 days old killed all field weevils after 14 days of exposure. The 150-day-old deposit of deltamethrin was also 100% effective against field weevils exposed for 14 days, while the effectiveness against selected populations was around 50%. Malathion deposits of the same age gave 40-50% mortality of field weevils, and 4-68% mortality of selected weevils. The 720-day-old deposits of malathion were ineffective against all weevil populations, while the mortality of laboratory weevils after 14 days contact with deltamethrin deposits of the same age was 76%, and that of field and selected weevils about 50%.