Laboratory Evaluation of Citrus Peel Essential Oils Against Pulse Beetle (Callosobruchus chinensis L.) in Stored Pulses

The pulse beetle Callosobruchus chinensis (Coleoptera: Bruchidae) is a major insect pest of stored food grains. It attacks cowpea, gram, soybean, and even processed products like flour, causing serious losses. In recent years, some essential oils have shown promise in controlling this pest. This study tested citrus peel essential oils - lemon, orange, sweet lime, and grapefruit - along with a control, at four concentrations (15, 20, 25, and 30%) over various exposure times, using a Completely Randomized Design with five replications. Observations were made for 168 h. Lemon oil was the most effective, reaching 90.9% mortality at 30% after 168 h. Sweet lime followed with 81.8%, grapefruit 78.3%, and orange 77.3% at the same rate and duration. The LC₅₀ values dropped steadily over time - lemon from 32.6% at 12 h to 19.5% at 168 h, sweet lime from 34.1% to 21.1%, and grapefruit from 36.7% to 21.8%. LC₉₀ values also fell, with lemon from 64.3% to 40.1%, orange from 65.1% to 48.7%, sweet lime from 71.4% to 46.5%, and grapefruit from 72.5% to 53.5%. Lemon oil had the fastest LT₅₀ (time to kill 50% of beetles), reaching 23.4 h at 30%, while orange and grapefruit at 15% took over 505.2 h. For LT₉₀, lemon oil reached 90% kill in 845.8 h at 30%, orange took 18,390.9 h at 15%, sweet lime 2,753.8 h, and grapefruit 7,276.0 h. In conclusion, all citrus peel oils reduced C. chinensis numbers, with mortality rising as concentration and exposure increased. Lemon oil was the most potent, followed by sweet lime, grapefruit, and orange. These results suggest that lemon oil - and to some extent sweet lime and grapefruit oils - could be used as eco-friendly protectants for stored pulses, offering a safe alternative to chemical insecticides in pest management programs.