Laboratory studies on protectants for control of Coleoptera in maize

Abstract

The effectiveness of nine protectant compounds was assessed on maize of 14% moisture content stored at 30°C. The order of potency of freshly-applied residues of organophosphorus compounds against multiresistant Tribolium castaneum (Herbst) and Sitophilus oryzae (L.) was chlorpyrifos-methyl>pirimiphos-methyl>methacrifos>fenitrothion. Chlorpyrifos-methyl was also the most potent compound against susceptible S. zeamais Motschulsky. The order of potency of synthetic pyrethroids against multiresistant Rhyzopertha dominica (F.) was deltamethrin > fenvalerate > permethrin and bioresmethrin > d-phenothrin. Minimum effective application rates for desired periods of protection depended on each protectant's inherent potency and on the rate at which its effectiveness was lost during storage, the latter seeming to correlate with published rates of chemical breakdown. For most protectants, application rates that have proved successful on wheat in Australia should also work on maize. Probable exceptions are methacrifos and deltamethrin (unsynergised) which, used alone, did not control R. dominica and Sitophilus spp, respectively, at realistic rates. The remaining compounds would be used in combination. Against T. castaneum, fenitrothion (12 mg kg −1) and pirimiphos-methyl (4 mg kg −1) completely prevented progeny for 3 and 9 months, respectively, although allowing some adult survival, and chlorpyrifos-methyl (10 mg kg −1) completely prevented progeny and killed adults of S. oryzae for 4.5 months. Against R. dominica, deltamethrin (0.04 mg kg −1), fenvalerate (0.25 mg kg −1), and permethrin (0.5–1 mg kg −1) gave complete protection for 9 months, but higher application rates were required using bioresmethrin and d-phenothrin.