Control of grain pests with phosphine at temperatures below 10C
About this project
Tests were conducted on the toxicity of phosphine to all stages of 5 species of stored grain beetles at 5, 7.5 and 10°C. Two strains of each species were tested, one a laboratory stock and the other of relatively recent acquisition from the field. Ahasvervs advena, Oryzaephilus surinamensis and the laboratory strain of Tribolium castaneum were all killed by the relatively low dosage of 0.1 mg/l phosphine held for 4 days at all temperatures tested. The field strain of T. castaneum, which proved to be phosphine resistant, and the two strains of Cryptolestes ferrugineus, required an 8-day exposure at 0.3 mg/l, or a 12-day exposure at 0.1 mg/l for control. The eggs and younger larvae of all species were adversely affected by the cold.
Older stages of Sitophilus granarius were highly tolerant both of cold and exposure to phosphine, and survived 15-day exposures to 0.64-1.35mg/l phosphine at 10°C, and even longer exposures at 5 and 7.5°C. As a result fumigation can only be recommended below 10°C in the absence of this species.
Adults were generally more susceptible to phosphine than immature stages, although this difference tended to reduce as temperatures were lowered. Times to end-point mortality were protracted and some individuals recovered from exposure after three days of incubation at 25°C. For phosphine resistant strains differences in tolerance between adult and immature stages are likely to be reduced at all temperatures and the presence of resistance will affect dosage recommendations.
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