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 major 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.