Biological-control of fungi and pink bollworm (Lepidoptera: Gelechiidae) by bacteria isolated from the caterpillars carcasses

Abstract

Lepidopteran insects, such as Spodoptera spp. and Pectinophora gossypiella, are major agricultural pests worldwide. This study focused on bacterial strains isolated from Lepidopteran larval carcasses, belonging to Pseudomonas, Bacillus, Klebsiella, Enterobacter, Providencia, Proteus, Enterococcus, Lysinibacillus, and Staphylococcus spp. Pseudomonas aeruginosa FCC7 and FCC25 caused 83 % larval mortality in Pec. gossypiella, and their pathogenicity was proven by Koch's postulates. Lysinibacillus fusiformis FCC12 and P. aeruginosa suppressed Aspergillus niger growth by 90 %, while Bacillus strains FCC22, FCC23, and FCC30 altered Fusarium solani mycelial structure. Additionally, these isolates possessed plant growth-promoting traits. Klebsiella pneumoniae FCC28 and K. quasipneumoniae SL17 produced 174 mg L⁻¹ and 133 mg L⁻¹ indole-3-acetic acid (IAA), respectively, after 80 h, while Providencia SL11 produced 83 mg L⁻¹ IAA within 20 h. In Klebsiella spp., IAA production began in the late log phase, remained elevated until the late stationary phase, and showed a positive correlation with pH. In contrast, Providencia SL11 exhibited growth-associated IAA production during the late log to early stationary phase, showing an inverse correlation with pH. 20 out of 28 isolates solubilized phosphate, with Bacillus FCC22 showing a phosphate solubilization index of 20. Klebsiella quasipneumoniae SL17 solubilized 42 mg L⁻¹ phosphate within 24 h and continued solubilization throughout the stationary phase, accompanied by a significant drop in pH from 6.5 to 4.5. The pH and solubilized phosphate concentration were inversely correlated with titratable acidity. These findings highlight the dual role of insect-associated bacteria in biocontrol and plant growth promotion. Further studies are needed to identify active compounds and develop cost-effective microbial formulations for sustainable agriculture.