Effectiveness of Malathion in Protecting Stored Polished Rice from Damage by Several Species of Stored-Grain Insects1

Malathion at 8 p.p.m. as dust or spray on polished rice gave excellent protection from damage by the rice weevil, Sitophilus oryzae (L.), during a 5-month storage period. Four p.p.m. gave complete protection from the flat grain beetle, Cryptolestes pusillus (SchOnherr.). Less protection from damage by the red flour beetle, Tribolium castaneum (Herbst), was obtained. Effectiveness of the residue against the rice weevil in a 4 p.p.m. treatment appeared to be decreasing at 3 months. Bioassay of malathion residue with adult rice weevils on rice after 5 months’ storage showed that at 8 p.p.m. a mortality of 100% was obtained after 10 days’ exposure.