Efficacy of Contact Insecticides for the Control of the Larger Grain Borer, Prostephanus truncatus (Horn), on Stored Maize

One of the most destructive insect species for stored maize is the larger grain borer, Prostephanus truncatus . Its control is challenging, as it seems to have a natural tolerance to active ingredients that are effective for other stored-product insect species that cause infestations in maize. The objective of the present study was to comparatively evaluate a wide range of insecticides that are currently in use in stored product protection for the control of P. truncatus . Specifically, three inert dusts—namely, a kaolin, a zeolite and a diatomaceous earth formulation—and three residual insecticides—i.e., the pyrethroid deltamethrin, the bacterial insecticide spinosad and the juvenile hormone analogue S-Methoprene—were evaluated against adults of P. truncatus . Adult mortality was assessed after 7, 14, 21 and 28 d of exposure, whereas progeny production was measured after an additional interval of 28 d for inert dusts and 65 d for the contact insecticides. Moreover, the number and weight of infested and uninfested kernels per vial was measured. Low mortality levels were recorded for the three inert dusts even for the highest application rate and after 28 d of exposure. Moreover, the inert dusts tested failed to suppress the progeny production of P. truncatus . In contrast, high mortality levels were recorded for deltamethrin and spinosad that exceeded 95% already after 7 d of exposure at the lowest application rate (0.5 ppm). The application of S-Methoprene did not result in high adult mortality rates, irrespective of the application rate and the evaluation interval. Deltamethrin, spinosad and S-Methoprene significantly suppressed progeny production of the species at the doses tested.