The effect of sublethal doses of Bacillus thuringiensis Berliner on Tuta absoluta (Meyrick) on resistant and susceptible tomato cultivars

Abstract

The effect of Bacillus thuringiensis (Bt) Berliner on the Tuta absoluta (Meyrick) on two resistant ('King Stone') and susceptible ('Rio Grande') tomato (Solanum lycopersicum L.) cultivars was studied under laboratory conditions. In the bioassay tests, the lethal concentration (LC 50 ) values of Bt were determined for the 2nd-and 3rd-instar larvae of T. absoluta on two cultivars. In another experiment, the effect of sublethal doses of Bt on 2nd-and 3rd-instar larvae on two susceptible and resistant cultivars was determined. Also, the nutritional indices and the enzyme content of larvae on two susceptible and resistant cultivars under the sublethal doses of Bt were investigated. All nutritional indices and the enzyme content of the treated larvae were significantly different compared to those of the control group. The lowest efficiency of the conversion of ingested food (7.82%), the efficiency of the conversion of digested food (4.34%), the relative consumption rate (22.29 mg mg −1 day −1 ), and the relative growth rate (1.16 mg mg −1 day −1 ) was determined for the resistant cultivar 'King Stone' at the LC 25 concentration of Bt. The lowest amount of α-amylase (0.98 nM min −1 mg −1 protein), protease (12.61 µM min −1 mg −1 protein), and lipase (0.182 nM min −1 mg −1 protein) and the highest amount of phenoloxidase (0.337 µM min −1 mg −1 protein) were determined for the resistant cultivar 'King Stone' at the LC 25 concentration of Bt. The results showed that the integration of Bt application and host plant resistance significantly increased the efficiency of Bt.