Susceptibility of different Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae) populations to indigenous Bacillus thuringiensis strains

Abstract

Tomato leafminer, Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae) is one of the most important tomato pests worldwide and causes 100% product loss if not controlled. Chemical insecticides, which have been overused for many years, have induced resistance in the pests and made it difficult to control their populations in the field. The use of biological agents that express insecticidal proteins, such as Bacillus thuringiensis, is an alternative to conventional insecticides to suppress pest populations. In this study, to recover novel B. thuringiensis strains from soil samples, a survey was conducted in Bilecik province in 2021. Thirteen local B. thuringiensis strains were isolated and the susceptibility of three different field populations (Samsun, Izmir, and Bilecik) of T. absoluta to these strains was evaluated. Bacillus thuringiensis B3 (Bt-B3) strain, which contains lepidopteran-active toxin genes, was more virulent for all T. absoluta populations tested. In addition, Samsun population was more sensitive to the B3 strain than Izmir and Bilecik. The LC50 values of Bt-B3 were determined to be 13.28, 26.06 and 24.24 ppm for Samsun, Izmir and Bilecik populations, respectively. Sequencing of the 16S rRNA gene region confirmed that the isolate was B. thuringiensis, while electron microscopy revealed that the isolate produced bipyramidal, cubic and spherical insecticidal proteins. The results of this study indicate that the isolate Bt-B3 appears to be a promising biocontrol agent for integrated pest management of T. absoluta in Turkiye.