Small bin trials to determine the effectiveness of acid-activated kaolin against four species of beetles infesting paddy under tropical storage conditions

Abstract

Control of populations of Rhyzopertha dominica, Sitophilus oryzae, Tribolium castaneum and Oryzaephilus surinamensis infesting paddy treated with acid-activated kaolin (AAK) at 0.75% w/w or with pirimiphos-methyl (PM) diluted with AAK to give 2 mg PM/kg paddy was compared with that in untreated paddy or paddy admixed with a 2% PM dust formulation on talc at 8 mg a.i./kg. Grain was stored in 45 kg lots in fibreboard drums for 250 days and subjected to periodic infestation with the beetles. All three treatments controlled adult populations of the insects up to 200 days post-treatment, but R. dominica populations started to increase at 250 days in the treatment using 2% PM dust, and this treatment gave progressively lower mortality of R. dominica and less suppression of progeny development in 7 day bioassays using samples taken through the trial than the other treatments. Mean % breakdown of PM formulated on AAK was about twice that on untreated kaolin in accelerated storage tests, and PM residues declined at a faster rate in paddy treated with the mixed dust formulations of AAK and PM than in paddy treated with the 2% PM dust formulation. The deactivator diethylene glycol could be incorporated at up to 10% w/w in AAK with negligible effect on the insecticidal activity of the dust to R. dominica.