Efficacy of diatomaceous earth to control internal infestations of rice weevil and maize weevil (Coleoptera: Curculionidae)

Densities of 10, 20, and 30 hard red winter wheat kernels, Triticum aestivum L., were infested with different life stages of the rice weevil, Sitophilus oryzae (L.), mixed with 35 g of wheat treated with 300 ppm of the Protect-It (Mississauga, Ontario, Canada) formulation of diatomaceous earth (DE), and held at 22, 27, and 32degreesC. A similar test was conducted by exposing densities of 6, 12, and 18 corn kernels infested with different life stages of the maize weevil, Sitophilus zeamais Motschulsky, mixed with 30 g of corn, Zea mays L., treated with 300 ppm of DE. Mortality of adults emerging from kernels in wheat treated with DE was always greater than controls, and ranged from 56 to 90% at 22degreesC and was >90% at 27 and 32degreesC. In most treatment combinations, exposure to DE suppressed F, progeny by 60-90% relative to untreated controls. Mortality of adult maize weevils on treated corn held at 22 and 27degreesC was lower than mortality of lice weevils on wheat, and ranged from 4 to 84%. F-1 production was low in corn held at 22degreesC, and no F(1)s were produced in either the controls or the treatments at 32degreesC. In treated corn held at 27degreesC, exposure to the DE suppressed F-1 progeny by approximate to70-80% relative to the untreated controls. Results of this study show that rice weevils and maize weevils emerging from infested kernels as adults are susceptible to DE, and these results are comparable to other studies in which adult weevils were exposed directly on wheat or corn treated with DE. Although adult weevils will be killed by exposure to DE, some oviposition could still occur and progeny suppression may not be complete; however, application of DE to commodities already infested with internal feeders, such as the rice weevil and the maize weevil, could help eliminate or suppress the infestation.