Bioactivity of raw diatomaceous earth against Rhyzopertha dominica Fab. (Coleoptera: Bostrichidae): Effects of grain type, dose rate and exposure period

Abstract

Laboratory experiments were carried out to evaluate the efficacy of raw diatomaceous earth (DE) against R. dominica on Maize: Zea mays (L.), sorghum: Sorghum bicolor (L.) (Moench) and wheat: Triticum aestivum (L). The tests were conducted under ambient laboratory conditions (26-34°C and 27-51% r. h.). Thirty adult insects were bioassayed on 50 g grain sample treated with the DE at five dose rates: 125, 250, 500, 1000 and 1500 ppm. Adult mortality, progeny production and percentage of insect-damaged kernels (IDK) were assessed. On all grain tested mortality increased with higher dose rate and longer exposure period. After 14 days exposure to the highest dose rate, adult mortality was 98.0±0.8, 93.2±1.8 and 99.3±0.75% on maize, sorghum and wheat, respectively. Progeny production was considerably suppressed on treated grains in comparison with the untreated respective controls but significantly influenced by grain type. Similarly, the percentage of IDK decreased with increase in dose rate. At 1500 ppm IDK in maize, sorghum and wheat were 1.2±0.5, 2.8±0.5 and 2.2±0.8 % as compared to 54.1±8.6, 45.1±1.8 and 84.1±1.75% in the untreated control, respectively. To provide effective control of R. dominica using the raw DE, dose rates higher than 1500 ppm are required.