Insecticidal efficacy of a binary combination of cyphenothrin and prallethrin, applied as surface treatment against four major stored-product insects

Abstract

In the present study, we investigated the insecticidal efficacy of a commercial binary combination of two pyrethroids, cyphenothrin and prallethrin, as structural treatment against adults of Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), Tribolium confusum Jacquelin du Val and Prostephanus truncatus (Horn) in laboratory bioassays. In a first series of bioassays, the insecticide was applied at its label dose on concrete and metal surfaces, whereas mortality and knockdown levels were recorded after 1, 3, 7 and 14 d of exposure. In a second series of bioassays, the residual efficacy of the insecticide was evaluated on concrete for a period of four months, stored either in continuous darkness or exposed to light. In these bioassays, mortality and knockdown of the exposed insects was measured after 3, 7 and 14 d of exposure. Finally, in a third series of bioassays, we investigated the immediate and delayed effect of the tested formulation on adults of the four insect species after exposure for 1, 3 and 7 d. Based on our results, the application of the tested insecticide as surface treatment can provide efficient control against adults of all four species tested. The surface type did not significantly affect the insecticidal efficacy of the tested formulation, at least for the surfaces tested. Moreover, exposure to light negatively affected the residual activity of the insecticide, as for all insect species tested, mortality was significantly lower on dishes exposed to light than on the ones stored in the dark for storage intervals equal or longer than two months. Finally, reduced delayed mortality was observed for all exposure intervals, as knocked down individuals remained, in most cases, knocked down even 7 d after their removal from the treated dishes.