Efficacy of rice husk ash against rice weevil and lesser grain borer on stored wheat

Abstract

Rice husks are an environmental nuisance, but have a high concentration of silica. Therefore, rice husk ash (RHA), a by-product of burning rice husks, may have potential for control of stored grain insect pests. The objective of this study was to determine efficacy of RHA from “Mr. Harry” rice variety against Rhyzopertha dominica and Sitophilus oryzae. Low (RHAL) and high (RHAH) application rates of RHA, corresponding to 0.5 and 1 g kg^-1, respectively, were evaluated against both weevils on wheat. Insecto®, a commercial DE, was tested as a standard check. This study was conducted at Oklahoma State University, Stillwater, OK, USA. RHAH caused 10.3 and 91.1% mortalities of adult R. dominica and S. oryzae, respectively, after a 14-day exposure period. After the same time period, Insecto® caused R. dominica and S. oryzae mortalities of 63.4 and 100%, respectively. For S. oryzae, Insecto®, RHAH and RHAL caused F1 progeny suppression of 95.2, 63.8 and 46%, respectively. Similar numbers of R. dominica progeny were produced in the control, RHAL, and RHAH treatments (78.4, 92.9 and 64.3, respectively); fewer progeny were produced in the Insecto treatment (20.3). The silica in RHA used was 87.1%. In relation to particle size, the mean, minimum, and maximum particle sizes for RHA were 112.4, 16.2, and 550.1 μm, respectively. Based on this study, RHA may have potential for refinement into an effective protectant for use in management of stored grain insect pests in sub-Saharan Africa.

Key Words: Oryza sativa, protectant, Rhyzopertha dominica, silica, Sitophilus oryzae