Biocontrol efficacy of native protease-producing bacterial isolates against the olive leaf moth, Palpita unionalis (Hübner) (Lepidoptera: Pyralidae)

Abstract

Abstract Background The olive leaf moth (OLM), Palpita unionalis (Hübner) (Lepidoptera: Pyralidae), poses a significant threat to olive cultivation. This study focused on isolating protease-producing bacteria from moribund field strains of P. unionalis larvae and assessing their larvicidal efficacy against laboratory strains through estimated LC30, LC50, and LC90 values. Additionally, the long-lasting impacts of LC50 values on pupal and adult stages were evaluated. Results Three entomopathogenic bacteria, Bacillus amyloliquefaciens, Pseudomonas putida, and Bacillus subtilis, were isolated. The larvicidal efficacies of these isolates varied, as B. subtilis exhibiting greater efficacy at LC30 and LC50 values, while P. putida showed the most potent effect at the LC90 value. Conversely, B. amyloliquefaciens demonstrated the lowest larvicidal potentialities at LC50 and LC90 values, with P. putida being the least effective at the LC30 value. The toxicity regression lines indicated increased larval lethality with each unit increase in concentration, as evidenced by the positive slope values. Chi-square (χ2) values suggested a better fit and supported the reliability of the estimated lethal concentrations. Exposure to LC50 values s resulted in significant elongation of larval duration and reduction in weight, whereas pupal lifespan, adult emergence, and sex ratio showed non-significant differences compared to untreated controls. Conclusions The study highlights the promising role of these biological candidates in pest control programs as eco-friendly alternatives, potentially enhancing safe plant production. The varied larvicidal efficacies of the bacterial isolates, along with their proteolytic capabilities, underscore their potential as biocontrol pathogens against OLM, contributing to sustainable agricultural practices.