Insecticidal efficacy of three vegetable oils as post‐harvest grain protectants of stored wheat against Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae)

The lesser grain borer, Rhyzopertha dominica is a major insect pests of stored grain in the tropics. Vegetable oils (chamomile, sweet almond and coconut) at 2.5, 3.5, 5.0, 7.0 and 10.0 mL/kg were tested against Rhyzopertha dominica (F.) in wheat grain. All bioassays were conducted at 30°C and 65%± 2% RH. Treatments with vegetable oils at high dose (10.0 mL/kg) achieved over 95% control within 24 h of exposure to freshly treated grain. There was little difference between the three oils in their effect. Persistence of oils in grains was tested at short‐term storage intervals (48, 72 and 96 h) and intermediate‐term intervals (10, 20 and 30 days) after treatments. The activity of all products decreased with storage period. Seed viability was reduced by the high dose rate (10.0 mL/kg) of oil treatments. The potential use of vegetable oils as supplementary or alternative grain protectants against insect damage in traditional grain storage in developing countries is discussed.