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)) + methoprene (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 on 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 were taken from 1 m below the grain surface at various times during storage to check for infestations, and to use in bioassays and residue analyses. The bioassays used resistant strains of Sitophilus zeamais Motschulsky, S. oryzae (L.), Rhyzopertha dominica (F.), Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (L.). The study confirmed that chlorpyrifos-methyl + methoprene and chlorpyrifos-methyl + synergized phenothrin were highly effective against the major grain beetles for at least 7 months. Both treatments gave good control of beetles in laboratory bioassays, and no infestations were detected in the silos despite the presence of beetles before treatment. The study also shows that methroprene would be an effective alternative to synthetic pyrethroids for control of R. dominica, and could be used in a rotation program as part of a resistance management strategy. Further study is required on the efficacy of protectants against the moth Ephestia cautella Walker, because infestations developed on the grain surface in each treatment.