Repellency and Toxicity of Azadirachtin and Neem Concentrates to Three Stored-Product Beetles

Abstract

Repellency and toxicity of azadirachtin (98% AZA, which contains 98% azadirachtin) and 3 neem extracts (48, 23, and 7% AZA) to 3 stored-product insects, the rusty grain beetle, Cryptolestes ferrugineus (Stephens), the rice weevil, Sitophilus oryzae (L.), and the red Aour beetle, Tribvlium castaneum (Herbst), were investigated in the laboratory. Each test material repelled all 3 species in a standard repellency test using a food preference apparatus. Significant negative correlations were found between insect settling response and extract concentrations. T. castaneum was more sensitive to the repellent action of neem than the other 2 species. The test materials were also toxic to the 3 pest species, with C. ferrugineus being the most susceptible. Six-week LC50 values for 48, 23, and 7% AZA for C. ferrugineus were 18.8, 37.0, and 127.3 ppm, respectively. The F1 adults of all 3 insect species in almost all treatments were significantly reduced compared with controls. This reduction was significantly dose dependent. The relationship between bioactivity of neem materials and their azadirachtin content was established and is discussed. We confirmed that azadirachtin was largely responsible for both repellent (behavioral) and toxic (physiological) actions of neem on stored-product insects. However, the neem extracts are slightly more active than pure azadirachtin when applied at equivalent azadirachtin concentrations, indicating that azadirachtin is not the only active compound in neem.