Insecticide Use Practice and Occurrence of Insecticide Resistance in Tomato Leaf Miner in the Central Rift Valley

Abstract

The tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is a majo insect pest of tomato in the Central Rift Valley (CRV) areas of Ethiopia. Tomato growers complain on the decline in efficacy of the insecticide registered for its control after the detection of the pest in the CRV in 2013. This decline in efficacy of the registered insecticides was hypothesized to be due to insecticide resistance development. Studies were conducted to understand the pesticide use practices against T. absoluta and to assess the occurrence of resistance in T. absoluta population. A survey in two kebeles each of five districts namely Lumme, Bora, Dugda and Adamitulu jido kombolcha of East Shewa zone and Hawassa Zuriya district of Sidama zone was conducted in April, 2017. A total of 44 farmers were interviewed using a structured questionnaire and information was gathered on different aspects of insecticide use. A leaf dip bioassay method was used to assess the occurrence of insecticide resistance using strains of T. absoluta collected from Hawassa, Meki, Awash Melkassa and Ziway areas. Bioassays were performed using insecticides from three classes namely Coragen 200 SC (chlorantraniliprole), Belt 480 SC (flubendiamide) and Radiant 120 SC (spinetoram) in six dilution rates including the recommended rate. Descriptive statistics were used to summarize the survey data. The bioassay data were analyzed using a probit model. Survey results showed that pesticides were generally applied at a higher rate and more frequently than recommended. The level of resistance to the three insecticides was observed to vary with the strains of T. absoluta. The level of resistance for chlorantraniliprole and flubediamide was higher than for Spinetoram. The LC50 values of all strains were far higher than the field rate for all the insecticides tested. Pesticide misuse and abuse were observed to be a common phenomenon in the study area. Higher LC50 values than the recommended field rates and higher resistance ratios suggest that the T. absoluta population in Ethiopia has developed resistance to the insecticides registered for its control. Efforts should be made in developing an Insecticide Resistance Management (IRM) strategy for effective and sustainable resistance management in the chemical control of T. absoluta.