Agricultural Entomology
Permanent URI for this collectionhttps://etd.hu.edu.et/handle/123456789/47
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Item ECOLOGY AND INSECTICIDE RESISTANCE MANAGEMENT OF THRIPS (THYSANOPTERA: THRIPIDAE) ON ONION (Allium cepa L.) IN THE RIFT VALLEY OF ETHIOPIA(Hawassa University College of Agriculture, 2020) BELETE NEGASHEcology and Insecticide Resistance Management of Thrips (Thysanoptera: Thripidae) on Onion (Allium cepa L.) in the Rift Valley of Ethiopia Belete Negash1 , Ferdu Azerefegne1 and Gashawbeza Ayalew2 1Hawassa University, College of Agriculture, Hawassa, Ethiopia 2 Ethiopian Institute of Agricultural Research, Melkassa Research Center, Adama, Ethiopia ABSTRACT Decline in efficacy of registered insecticides to control thrips (Thysanoptera: Thripidae) on onion in Ethiopia stimulated studies on insecticide resistance, ecology and management of thrips on onion in the major onion production belt of the Central Rift Valley of Ethiopia (CRV). Several studies including farmers‟ insecticide use practices against thrips on onion, species composition and abundance, seasonal abundance of thrips and their effect on yield, insecticides resistance detection and management were conducted from 2015 to 2017. Diazinon, dimethoate, profenofos, lambda-cyhalothrin and spinetoram were widely used for thrips control on onion in the surveyed areas. Type and frequency application of insecticides use were different among the locations. Insecticide application frequencies were higher at Meki and Melkassa than in Werer areas. All the onion fields visited during the survey were infested by two thrips species namely, the western flower thrips, Frankliniella occidentalis (Pergande) and the onion thrips, Thrips tabaci (Lindeman). Thrips species compositions vary with locations. While, T. tabaci was dominant in Werer and Melkassa areas. The F. occidentalis thrips species was dominant at Meki location. Thrips population was higher during mid-growth stage of onion, 50 to 64 days after transplanting, than early and late growth stages in cool dry (October–January), hot dry (February – may) and rainy (June – September) growing seasons. Significantly lower thrips population recorded in the rainy season than the cool dry and hot dry seasons. Onion growth stage, growing seasons and sunshine hours were important factors for predicting thrips numbers. Cool and rainfall seasons significantly negative correlated with thrips numbers, while it was positively correlated with the onion growth stage, maximum temperature and sunshine hours. Thrips number was significantly greater on untreated plots than insecticide treated plots except in the rainy season. Higher percent yield losses were recorded on planting made in cool dry and hot dry 2 seasons in both years than rainy season with 8.24 to 40.17% yield losses. Commonly used insecticides on thrips were evaluated for their efficacy both in field and laboratory condition. Plots treated with spinosad, spinetoram, and imidacloprid resulted in better control, which was comparable higher marketable yield of onion both in cool and hot dry seasons. While, alphacypermethrin, diazinon, neem and λ-cyhalothrin insecticides treated plots poorly performed in both seasons and had lower marketable yield. Performances of dimethoate and profenofos were intermediate with the intermediate yield gains over the control under field condition. Laboratory bioassay confirmed that the poor efficacy of λ –cyhalothrin and diazinon under field conditions was due to thrips resistance to these insecticides. Higher level of resistance was recorded to λ – cyhalothrin and diazinon in Meki and Melkassa collected thrips populations, whereas no resistances to profenofos, dimethoate and spinetoram insecticides in all tested thrips populations were found. From insecticides resistance management studies, the sequential application of the more effective insecticides, imidacloprid and spinetoram, followed by less effective insecticide λ-cyhalothrin resulted in better control with higher economic return. Adding a penetrating surfactant improved the efficacy of insecticides compared to those without a penetrating surfactant in both seasons. Onion growers will continue to rely on insecticides as part of thrips management. Hence screening of new molecules periodically to identify effective insecticides and deploying a resistance management strategy through, among others, rotational application should form integral component in the integrated management of thrips (IPM) on onion. Studies on non-chemical control methods including cultural such as intercropping with other vegetables, host plant resistance should be conducted with the aim of strengthen thrips IPM