Sorption and insect toxicity of propylene oxide in dried fruits and nuts.

Dried fruits and nuts were fumigated with a mixture of propylene oxide (PPO) and CO₂ (8%:92% w/w) in 28.42-litre chambers to determine PPO sorption rates in these products and toxicity to a variety of postharvest insect pests. A 48-h fumigation using a rate of 45 mg/litre at 38°C resulted in more than 97% sorption in almonds, pecans and walnuts, and induced 100% mortality of mixed life stages of the following insects: Indian meal moth (Plodia interpunctella), red flour beetle (Tribolium castaneum), confused flour beetle (T. confusum), warehouse beetle (Trogoderma variabile), cigarette beetle (Lasioderma serricorne), lesser grain borer (Rhyzopertha dominica) and saw-toothed grain beetle (Oryzaephilus surinamensis). The 48-h fumigations resulted in PPO residues in the nuts that were below the tolerance level (300 ppm). The residues dropped to undetectable levels following aeration for 3 days. A 24-h fumigation of walnuts, raisins and figs infested with P. interpunctella, Trogoderma variabile and dried fruit beetle (Carpophilus hemipterus) using a rate of 75 mg/litre at 26.7°C resulted in 78, 95 and 93% sorption, respectively, but failed to provide complete mortality of the insects. Susceptibility to PPO was C. hemipterus > P. interpunctella > T. variabile. The rate of PPO sorption into walnuts, raisins and figs was independent of rate.