Large-scale evaluation of the insect juvenile hormone analogue fenoxycarb as a long-term protectant of stored wheat

Abstract

The potential of the insect juvenile hormone analogue fenoxycarb to protect wheat against infestation by 4 major beetle pests of stored grain has been investigated over a 2-yr period. Tests were carried out under simulated practical conditions, whereby small bulks (approx. 0.6 tonnes) of treated grain were infested at 0, 6, 12 and 18 months with 300 adults of each of Tribolium castaneum, Oryzaephilus surinamensis, Rhyzopertha dominica and Sitophilus granarius. Following treatment and the first introduction of insects, grain samples were examined at three month intervals for the presence of insects, the quality of the grain and the levels of pesticide remaining in the grain. In addition, grain samples were assessed for milling and baking quality, and insecticide residues were measured in white flour, bran and baked white bread. The efficacy of fenoxycarb (applied at 4.2 or 8.2 mg/kg a.i.) was assessed by comparison with results obtained with untreated grain and with grain treated with a conventional insecticide (chlorpyrifos-methyl) applied at 3.9 mg/kg a.i. Treatment of grain with chlorpyrifos-methyl (3.9 mg/kg) controlled populations of O. surinamensis for 9 months, populations of R. dominica and T. castaneum for 12 months, and populations of S. granarius for 15 months. Treatment of grain with fenoxycarb at 4.2 mg/kg controlled populations of O. surinamensis, R. dominica and T. castaneum for 2 yr, but was not completely effective at controlling populations of S. granarius. Treatment of grain with fenoxycarb at 8.2 mg/kg controlled populations of all 4 species for the entire 2 yr period of the trial. Grain quality and breadmaking properties were maintained better when populations of insects were kept low. Residues of chlorpyrifos-methyl and fenoxycarb were low in white flour and baked white bread, but residues were markedly higher in bran.