Characterization of a local Bacillus thuringiensis isolate (BtTuM1) and its potential as an entomopathogenic agent against Tuta absoluta

Abstract: The tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a
major pest in tomato cultivation, causing yield losses of up to 100 % in Turkey and worldwide. This pest damages all above-ground plant organs. Although chemical control is commonly used, its efficacy is limited due to the pest’s endophytic larval lifestyle, high biotic potential, multivoltine development, and increasing resistance to insecticides. Therefore, sustainable strategies such as integrated pest management (IPM), that includes biological control, are essential for effective management of this pest. The integration of biopesticides, such as those containing Bacillus thuringiensis (Bt) or other microorganisms, into IPM programs offers significant benefits. Additionally, the use of local natural enemies, including parasitoids, predators, and microbial pesticides, further minimizes undesirable ecological impacts. This study evaluated the potential of a local Bt isolate (BtTuM1), obtained from T. absoluta larvae collected in Muğla Province (Türkiye), for use in biological control of this pest. Laboratory analyses assessed the isolate’s phenotypic, genotypic and pathogenic characteristics. BtTuM1 showed robust growth on various media, including Nutrient Agar (NA), Sucrose Nutrient Agar (SNA), King B (KB), Yeast Dextrose Calcium Carbonate Agar (YDCA), and Trypticase Soy Agar (TSA), forming large, circular, flat colonies with wrinkled surfaces and yellowish-cream coloration. The isolate was determined to be Gram-positive based on a potassium hydroxide (KOH) test and oxidase-positive as indicated by a blue reaction on oxidase test paper. Spore and crystal staining revealed green-stained spores and purple crystals within red vegetative cells under light microscopy (100 × magnification). Molecular analyses confirmed the presence of cry1, cry2, and vip3 toxin proteins, which are effective against lepidopteran pests. Bioassay results demonstrated that BtTuM1 caused more than 70 % mortality in T. absoluta neonate larvae within four days at a concentration of 10⁸ cfu/ml. These results suggest that the BtTuM1 isolate has significant potential for incorporation into IPM strategies targeting T. absoluta.