Exploring Arid Soils as a Source of Bacillus thuringiensis Biocontrol Agents Active Against Dipteran and Lepidopteran Larvae

Microbial communities found in arid environments often exhibit unique genetic and metabolic adaptations that enable them to synthesize potent bioactive compounds. Bacillus thuringiensis (Bt) is widely recognized for its biocontrol potential against various insects. This study aims to investigate the insecticidal potential of Bt strains isolated from Qatar’s soil against dipteran and lepidopteran larvae. The microscopic analysis identified distinct crystal types, including bipyramidal, cuboidal, spherical smooth, and spherical rough forms, with distinct cry, cyt, and vip genes. Strains producing bipyramidal crystals carry cry1A, cry2A, and vip3A genes, while only two strains producing spherical crystals carry cry4B and cyt1A genes. Bipyramidal crystal-producing strains (QBT552 and QBT877) showed potent insecticidal activity, achieving 100% mortality against Corcyra cephalonica larvae, with LC50 values of 25 µg/g. Spherical smooth crystal-producing strain (QBT862) exhibited high toxicity against Culex pipiens insect larvae (LC50 = 2 µg/L). The quantification of bipyramidal crystal protein production of strains QBT877 and QBT552 exhibited the highest δ-endotoxin yield (1334.4 ± 6.7 and 1188.7 ± 5.0 µg/mL, respectively), while smooth spherical crystal strains QBT758 and QBT862 were 577.5 ± 8.4 and 567.6 ± 8.4 µg/mL, respectively. These findings highlighted the potential of Bt QBT strains for biocontrol applications, with strains showing promise for producing effective δ-endotoxins.