Efficacy and Limitations of Phosphine "Spot-Fumigation" against Five Coleoptera Species of Stored Product Pests in Wheat in a Grain Store - Short Note

Field validation of spot-fumigation with phosphine (PH3) applied by a subcontracted pest-control company in a farm grain store infested by pests was conducted. Inside and outside of the fumigated grain spot, containers with adults of 5 species of coleopteran stored-product pests were regularly spaced. The beetle pests were the internally feeding Sitophilus granarius and Rhyzopertha dominica, and the externally feeding Tribolium castaneum, Oryzaephilus surinamensis, and Cryptolestes ferrugineus. A 100% mortality of all pest species inside the fumigated spot under the sheet used for the application was stated. The efficacy (maximal) sharply declined with the increasing distance from the fumigated spot: 50% mortality was observed at 5 m from the spot, 38% mortality at 10 m, and a mortality of 23% was observed at 15 m. Mortality was different among the species, and the most sensitive was O. surinamensis, whereas the most tolerant were S. granarius, R. dominica, and T. castaneum. Although an efficient fumigation within the spot was found, the efficacy was low in the grains surrounding the spot. The practical implications of the findings are discussed.