Efficacy of two formulations of pirimiphos-methyl as surface treatment against Sitophilus granarius, Rhyzopertha dominica, and Tribolium confusum

Abstract

In the present work, the insecticidal effect of two pirimiphos-methyl formulations [emulsifiable concentrate (EC) and capsule suspension (CS)] as surface treatment on concrete, plywood, galvanized metal, plastic, and ceramic tile was evaluated in laboratory bioassays against Sitophilus granarius (L.), Rhyzopertha dominica (F.), and Tribolium confusum Jacquelin du Val. Pirimiphos-methyl was applied at two-dose-rates, 0.01 and 0.1 mg/cm(2), and insect mortality was assessed after 1, 2, 3, 4, 5, 6, and 7 days of exposure. After the final mortality count, alive individuals were transferred to untreated dishes, and delayed mortality was evaluated after an additional period of 7 days. In another series of laboratory bioassays, the residual efficacy of these two pirimiphos-methyl formulations on concrete was evaluated against S. granarius, R. dominica, and T. confusum. Pirimiphos-methyl was applied at two-dose-rates, 0.01 and 0.1 mg/cm(2), on concrete dishes which were either kept in continuous darkness or exposed to light. A bioassay was initiated at the day of storage and every 4 weeks for 4 consecutive months (5 bioassays in total). Mortality of the exposed adult beetles was measured after 3 and 7 days of exposure. Both formulations were highly effective, with S. granarius being the most susceptible species. In general, mortality of the exposed beetles was not significantly affected by the surface type, with the exception of the significantly lower mortality counts of S. granarius adults on ceramic tile. CS appeared to be much more persistent on concrete than EC for all three species tested. Moreover, CS was not affected by light. In contrast, in some of the combinations tested, EC performance was poor in dishes that were exposed to light, in comparison with dishes that were in continuous darkness. We conclude that the surface type does not significantly and consistently affect S. granarius, R. dominica, and T. confusum mortality after surface application of the two pirimiphos-methyl formulations tested. Furthermore, CS can provide long-term protection when applied on concrete surfaces.