Abstract
Filter cake and Triplex powders from Ethiopia were applied to maize and wheat in the laboratory to determine efficacy against the lesser grain borer, <i>Rhyzopertha dominica</i> (Fabricius) (Coleoptera: Bostrichidae); maize weevil, <i>Sitophilus zeamais</i> Motschulsky (Coleoptera: Curculionidae); and rice weevil, <i>Sitophilus oryzae</i> (Linnaeus) (Coleoptera: Curculionidae). These species are major insect pests associated with stored grain in Ethiopia. Efficacy of the two powders was determined by exposing 20 adults of each species to 100 g of maize and wheat treated with 0, 0.3, 0.5, 0.7, 1, 2, 3, 4 and 5 g/kg of filter cake, and 0, 0.5, 0.7, 1, 2, 3, 6, 8 and 10 g/kg of Triplex. Adult mortality was determined 14 d after exposure to untreated and treated grain. Adult progeny production at each species-powder-concentration combination was determined at 42 d. Complete mortality (100%) of <i>R. dominica</i> was achieved on maize treated with 3–5 g/kg of filter cake; however, on maize 100% mortality of <i>S. zeamais</i>, and <i>S. oryzae</i> was not achieved at any of filter cake concentrations. Complete mortality of <i>R. dominica</i> adults was observed on wheat treated with 2–3 g/kg of the filter cake. Complete mortality of <i>S. zeamais</i> and <i>S. oryzae</i> was achieved when adults were exposed to wheat treated with 0.7–3 g/kg of filter cake. Mortality was less than 100% at all Triplex concentrations on maize and wheat for all three species. Adult progeny production of <i>R. dominica</i> was wholly suppressed at filter cake concentrations of 1–5 g/kg on maize, whereas progeny production of <i>S. zeamais</i> and <i>S. oryzae</i> on maize was not entirely suppressed at any of the filter cake concentrations. No progeny of <i>R. dominica</i> was observed on wheat treated with 2–3 g/kg of filter cake. Similarly, progeny production of <i>S. zeamais</i> and <i>S. oryzae</i> was completely suppressed on wheat treated with 3 g/kg of a filter cake. Complete suppression of progeny production of the three species was not achieved at any concentration of Triplex on both maize and wheat. These powders have potential in managing <i>R. dominica</i>, <i>S. zeamais</i>, and <i>S. oryzae</i> infesting maize and wheat.
Highlights
Most of the sub-Saharan African countries store their grains in traditional structures which are not insect proof [1, 2]
The mean ± SE mortality of R. dominica adults exposed to filter cake treated maize ranged from 2.3 ± 1.1 to 100% and those exposed to Triplex treated maize ranged from 0 to 45.0 ± 5.8%
Complete mortality of R. dominica was observed when adults were exposed to maize treated with 2–5 g/kg of filter cake
Summary
Most of the sub-Saharan African countries store their grains in traditional structures which are not insect proof [1, 2]. Grain storage losses in Ethiopia due to insect pests were estimated to be in the range of 10-21% [1], consistent with losses in other sub-Saharan countries. Tefera and his colleagues [4] reported the post-harvest loss in Ethiopia to range from 20 to 30%. Major insects that contribute to postharvest loss of cereals and pulses in Ethiopia include grain weevils, grain borers, grain beetles, and grain moths [1, 2]. The lesser grain borer, Rhyzopertha dominica (Fabricius); maize weevil, Sitophilus zeamais Motschulsky; and rice weevil, Sitophilus oryzae (Linnaeus) are cosmopolitan insect pests [5], and are considered as primary insect pests of stored grains in Ethiopia [1, 2, 6]
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