CHLORPYRIFOS-METHYL PLUS EITHER METHOPRENE OR SYNERGIZED PHENOTHRIN FOR CONTROL OF COLEOPTERA IN MAIZE IN QUEENSLAND, AUSTRALIA

Silo-scale field trials of chlorpyrifos-methyl (10 mg kg(-1)) + methop rene (1 mg kg(-1)) and chlorpyrifos-methyl (10 mg kg(-1)) + phenothrin (1 mg kg(-1)) + piperonyl butoxide (8.5 mg kg(-1)) were carried out o n maize in north Queensland, Australia. Although these treatments are known to be effective against insects in wheat stored under Australian conditions, they have not been assessed on maize. Samples of maize we re taken from 1 m below the grain surface at various times during stor age to check for infestations, and to use in bioassays and residue ana lyses. The bioassays used resistant strains of Sitophilus zeamais Mots chulsky, S. oryzae (L.), Rhyzopertha dominica (F.), Tribolium castaneu m (Herbst) and Oryzaephilus surinamensis (L.). The study confirmed tha t chlorpyrifos-methyl + methoprene and chlorpyrifos-methyl + synergize d phenothrin were highly effective against the major grain beetles for at least 7 months. Both treatments gave good control of beetles in la boratory bioassays, and no infestations were detected in the silos des pite the presence of beetles before treatment. The study also shows th at methroprene would be an effective alternative to synthetic pyrethro ids for control of R. dominica, and could be used in a rotation progra m as part of a resistance management strategy. Further study is requir ed on the efficacy of protectants against the moth Ephestia cautella W alker, because infestations developed on the grain surface in each tre atment.