Determination of the economic threshold level of tomato leaf miner, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) on tomato plant under glasshouse conditions

Tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera:Gelechiidae) is an important pest of tomato crops native to South America. It is considered to be one of the major pests of tomato crop in Ethiopia since 2012. The aim of this study was to determine the economic threshold level of T. absoluta under glasshouse conditions. The damage potential and economic threshold level for T. absoluta larvae on tomato crop were studied during 2015 to 2016 under glasshouse conditions. Significant (P < 0.05) differences were observed among the treatments during the study period. The number of larvae per plant reduced the yield to the extent of 10.51 to 75.62% during 2015, and 11.87 to 80.22% during 2016 cropping season. The mean values of marketable yield gained to the cost of insecticide application at 0, 1 and 4 larvae per plant were 34,913, 31,006 and 16,574.5 kg/ha from 2015 to 2016, respectively. The lowest yield was observed at control/unsprayed treatment (7,751.5 kg/ha). The economic injury level (EIL) lies at the pest population density where Benefit-Cost ratio would be 1.08. From this study, the ElL of T. absoluta was determined as 3.0 larvae per plant based on the findings of glasshouse experiments conducted over the period of two years. The economic threshold level (ETL) was worked out at 2.25 larvae per plant during the same years under glasshouse conditions.    Key words: Economic, infestation, injury, larva, management, threshold, tomato, Tuta absoluta, yield.