Chlorpyrifos‐methyl plus bioresmethrin; Methacrifos; Pirimiphos‐methyl plus bioresmethrin; and synergised bioresmethrin as grain protectants for wheat

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Abstract
Field trials with various pesticide combinations were carried out on bulk wheat in commercial silos in Queensland, South Australia and Western Australia. Laboratory bioassays on samples of treated grain at intervals over 8 months using malathion‐susceptible and malathion‐resistant strains established the following orders of efficacy: against Sitophilus oryzae (L.), chlorpyrifos‐methyl 10 mg kg−1 + bioresmethrin 1 mg kg−1 = methacrifos 15 mg kg−1 in aerated storage > pirimiphos‐methyl 4 or 6 mg kg−1 + bioresmethrin 1 mg kg−1 = bioresmethrin 4 mg kg−1 + piperonyl butoxide 16 mg kg−1; against Rhyzopertha dominica (F.), bioresmethrin 4 mg kg−1 + piperonyl butoxide 16 mg kg−1 > methacrifos 15 mg kg−1 > chlorpyrifos‐methyl 10 mg kg−1 + bioresmethrin 1 mg kg−1 = pirimiphos‐methyl 4 or 6 mg kg−1 + bioresmethrin 1 mg kg−1. All treatments completely prevented production of progeny in Sitophilus granarius (L.), Tribolium castaneum (Herbst), T. confusum Jackquelin du Val and Oryzaephilus surinamensis (L.). The biological efficacy of methacrifos was greater and the rate of degradation lower in aerated than in non‐aerated storage. Residue levels of all compounds were determined chemically and were below proposed international residue levels to be considered by the Codex Alimentarius Commission.