Efficacy of <i>Bacillus thuringiensis</i> Against the Tomato Leaf Miner, <i>Tuta absoluta</i> (Meyrick)

Abstract

The tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an introduced serious insect pest of tomato  in Ethiopia. Research on the management of this pest has so far been limited to screening of synthetic  insecticides. Owing to the pest's ability to develop resistance to insecticides quickly, biological based approach in its  management is a viable option. The study was conducted at Melkassa Agricultural Research Center in 2014. The  objectives of the study were to assess the efficacy of the microbial insecticide Bacillus thuringiensis (Bt) and the  optimum rate and frequency of its application. The tomato variety ‘Miya’ was used for this experiment. The experiment  was laid out in a factorial RCBD with three replications. The treatments consisted of four doses of Bt, 0.5, 1, 1.5 and 2kg  per ha applied at 7, 14 and 21 days intervals. Lambda cyhalothrin 5% EC (Karate®) and Chlorantraniliprole 240 SC  (Coragen ®) at 320 and 250 ml per ha, respectively were applied biweekly as standard checks along with the untreated  control. Egg density, leaf damage score, proportion of damaged fruit by number and weight, and marketable yield were  used to assess performance of the treatments. Differences for egg density were insignificant (P<0.05) among  treatments. Plots treated with the highest rate of Bt (2 kg per ha) at 7 days interval suffered less damage and resulted in higher marketable yield than the rest of Bt treatments. The lowest fruit damage level of 18.7 % was recorded from  Coragen treatment and the highest (81.8%) was recorded from the untreated control. The highest marketable yield of  28.39 tonnes per ha and the lowest of 3.25 tonnes per ha were recorded from Coragen and lowest Bt rate applied  triweekly, respectively. This corresponds to a yield loss of 88.5%. The study demonstrated the potential of Bt in reducing  damage and yield loss due to T. absoluta on tomato when applied with high dose (2 kg per ha) weekly. It is suggested that future studies need to look into assessing performance of higher doses and shorter application intervals than  considered in this study along with economics of their use in tomato production.