Grain borers are becoming resistant to pesticides

A lesser kind of grain borer (Rhyzopertha dominica Fabricius) is becoming resistant to phosphine- a type of fumigant or substance that is used to disinfect stored grains and protect them from pests.

Phisphine has been popularly used since the 1980 because it is easy to apply and does not leave any harmful residues in the grain.

The first signs of resistance were recorded in the early 70s but the resistance levels then wer low to pose a serious problem. Today, however, there are widespread reports of higher phosphine reisitance in some countries, which resulted to more researches in grain borers and phosphine resitance.

A survey in 1995 indicated that R. Dominica strains that are phosphine-resistant are present in the Philippines. The survey used the resistance method recommended by the Food and Agriculture Organization (FAO). It involves exposing adult grain borers to phosphine dose of 0.08 mg/liter phospine for 20 hours at 25 degrees centigrade and 70 percent relative humidity.

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