Fumigation toxicity of allicin against three stored product pests

• The potential of allicin as a grain fumigant was investigated.
• Higher allicin concentration reduced fumigation time and vice versa.
• The presence of wheat affected allicin toxicity against several grain insects.
• A constant percentage of allicin was sorbed by the fumigated wheat daily.

The fumigant toxicity of allicin against the adults, larvae and pupae of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) and Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae) was investigated under laboratory conditions. Results showed that for 6 d exposure of adults of these three species to allicin, the LC50 was 0.38, 0.51 and 0.51 μL/L of air, respectively, and the corresponding LC99 values were 1.11, 8.40 and 2.18 μL/L of air, respectively. The LC50 for larvae was 0.11, 0.12 and 0.36 μL/L of air after only 3 d exposure, respectively, indicating that the larvae were much more sensitive to allicin than adults. The pupal emergence of T. castaneum, O. surinamensis and C. ferrugineus was reduced to 85.6, 94.4 and 100%, respectively, after allicin treatment with a concentration of 5 μL/L of air. Trials using allicin in containers filled to 50% of capacity with wheat to imitate commercial conditions resulted in LC99 values for 6 day exposure of 19.7, 32.1 and 26.9 μL/L of air for adults of the three species, respectively. Head space solid phase microextraction (HS-SPME) combined with gas chromatograph (GC) analysis indicated that the concentration of allicin (615 μL/L) in the sealed fumigation vessels decreased to 6.21 μL/L of air after 1 d fumigation and 1.54 μL/L of air after 6 d of fumigation in sealed bottles, respectively. The concentration of allicin decreased quickly as aeration times increased, with less than 0.05 μL/L of air after 16 d aeration regardless of the fumigation time. These results suggest that allicin may be suitable as an active ingredient in a botanical fumigant.