Efficacy of deltamethrin emulsifiable concentrate against stored-product insects

Abstract

Stored-product insects are specially adapted to dry conditions and to a diet of grains and grain dust. Under favorable environmental conditions, insect populations multiply rapidly and spread in stored food. Prevention of pests' development can be achieved by a variety of methods, including the use of insecticides. Deltamethrin is a synthetic pyrethroid commonly used as an insecticide in grain storage. In Israel, deltamethrin emulsifiable concentrate (Keshet 2.5% EC) is the only pyrethroid insecticide formulation permitted for use in stored grain. Although deltamethrin is used routinely, insect populations develop consistently in warehouses and newly stored grain is rapidly infested. In the current study, we examined the efficacy of deltamethrin emulsifiable concentrate for the control of adult Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). The insecticide was sprayed on surfaces including plastic, self-made concrete, two kinds of ready-mix concrete, as well as harvested wheat. When deltamethrin concentrations of 0.2–2.0 ppm was applied to the grain, insect mortality increased with the application rate, with complete mortality observed at 2.0 ppm. A dose of 0.2 ppm was found to be insufficient to protect the grain. Plastic surfaces and surfaces of different types of concrete were sprayed with a 4% aqueous solution of deltamethrin emulsifiable concentrate (deltamethrin concentration 0.1 mg/m2). Deltamethrin emulsifiable formulation was found to be effective on a nonporous surface and when sprayed directly on insects, but was not very effective as a residual insecticide on porous surfaces.