Current status of phosphine resistance in stored grain insects in Malaysia

M. Rahim, M.E. Faridah and M. Rasali

Abstract

A survey was conducted in 2001 to determine the current status of phosphine resistance among insects infesting grain mills and stores in all states of Malaysia. The objective was to compare resistance levels with those of earlier surveys and to evaluate weaknesses in the conduct of fumigations. Four species of grain beetles were collected from 13 states and were tested with discriminating doses according to the standard FAO method. Resistance was recorded in 9 of the 13 states surveyed. All samples of the important primary species Sitophilus oryzae and Sitophilus zeamais were susceptible as in earlier surveys. Resistance is prevalent among the two most common secondary species, Tribolium castaneum and Oryzaephilus surinamensis. The 57% premises found to contain resistant populations of either or both species did not show an upward trend in the spread of resistance. Although Rhyzopertha dominica was frequently found, the surviving individuals from collected samples were insufficient for testing. Due to substandard fumigation of wheat and maize in silos, samples from these imported grain contained higher frequencies of resistant insects (87.5%) than samples from rice/paddy (44%). Resistant populations could be returned to a susceptible state by maintaining high standard of gastightness, by not overdosing, and using alternative pest control techniques.

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