Insecticidal impact of alumina powders against Acanthoscelides obtectus (Say)

For long-term protection of stored products there is a growing demand to replace chemical insecticides due to their effects on human health and environmental safety. Particulate materials, such as inert dusts and various submicron and nanomaterials have been extensively tested as viable alternatives. This is the first study on the insecticidal impact of alumina powder (α-Al2O3) on the bruchid pest, Acanthoscelides obtectus (Say) (Coleoptera: Chrysomelidae: Bruchinae). By altering the fuel to oxidant molar ratio (F/O: 0.5, 0.8, 1.2) in an autocombustion reaction we synthesized alumina powders with specific surface area and particle size varying from the nano- to micron scale. It was found that particle morphology influenced survival and progeny number of A. obtectus. The order of powders from low to high efficacy in reducing beetle performance (F/O-0.8 < F/O-0.5 < F/O-1.2) correlated well with increase in surface area, pore volume and diameter, and decrease in particle size. Survival was also affected by time of exposure, the applied dose and sex. The estimated median lethal concentration of the most efficient powder F/O-1.2 was significantly lower in males (LC50 = 330.4 ppm) than in females (LC50 = 409.6 ppm). Our results suggest that alumina powder can be considered for seed protection against A. obtectus, particularly during long-term storage, as it is cost effective, exerts limited toxicity to humans and demands no repetitive use like conventional pesticides.