Biological activity of Bacillus spp. evaluated on eggs and larvae of red palm weevil Rhynchophorus ferrugineus

This study was conducted to characterize the Bacillus populations associated with dead Rhynchophorus ferrugineus, to develop a biological control for the red palm weevil. Dead adult beetles, collected throughout Sicily, were used for isolating internal and external spore forming bacteria (SFB) microbiota. The isolates, preliminarily allotted to the Bacillaceae family, were tested at 4 concentrations (103 to 106 CFU/mL) for their ability to inhibit hatching of eggs of R. ferrugineus and were used at 106 CFU/mL to monitor their insecticidal activity against 10 day-old larvae. Total amounts of SFB measured outside the skeleton and in the inners part of the beetles were 5.59-6.94 and 5.17-7.05 Log CFU/g, respectively. Hatching was inhibited markedly by 9 isolates, representing 9 distinct strains of 7 species (Bacillus amyloliquefaciens, Bacillus cereus, Bacillus licheniformis, Bacillus megaterium, Bacillus pumilus, Bacillus subtilis, and Lysinibacillus sphaericus), especially by the strains B. pumilus GC43 and GC51, which exhibited lethal concentrations 50 (LC50) values of 1.60 × 103 and 9.84 × 103 CFU/mL, respectively. Among all the strains tested, only B. licheniformis CG62 exhibited significant insecticidal activity against red palm weevil larvae. The Bacillus isolates characterized and tested in this study inhibited the hatching of red palm weevils in a contact-dependent manner. Thus, these isolates can be used as a preventive rather than as a curative treatment. Keywords Bacillus, Rhynchophorus ferrugineus, hatching assays, larvae, Palm