Effect of entomopathogenic fungi against banana pseudostem weevil Odoiporus longicollis (Olivier) and elucidation of infection process

Abstract

Background: The banana stem weevil, Odoiporus longicollis (Olivier), is a serious threat to banana cultivation world over. Since banana is a food crop, the use of naturally infecting biological control agents could be an effective alternative to manage the insect pest instead of harmful chemicals. Also, the efficacy of entomopathogenic fungi against O. longicollis was used in bioassay. Results: Among the Beauveria bassiana isolates tested the median lethal concentration (LC50) 10.468 × 105 conidia ml−1 when treated with B. bassiana (NRCBEFPMP1), two other isolates of B. bassiana, namely NRCBEPF22 and NRCBEPF2, were also effective against O. longicollis and recorded LC50 of 12.617 × 105 and 12.891 × 105 conidia ml−1, respectively. The results of bioassay with different Metarhizium spp. showed variations in efficacy, where the most virulent isolate was M. quizhouense (NRCBEPF11) with LC50 8.050 × 105 conidia ml−1. Scanning electron microscopic analysis showed that B. bassiana and M. quizhouense caused infection by cuticle penetration and completed the infection process in 15 days. The composition of volatile organic compounds released by B. bassiana and M. anisopliae during pathogenesis showed that a significantly high number of known insect volatiles were present in infected insects. Consequently, these volatiles were emission in Insect attractant, Odorant receptor agonist, Plant hormone Plant, and Microbial Metabolites, through the biological activity, such as Methyl salicylate, Benzaldehyde, alpha-Terpineol, Limonene, Benzene, 1,2-dimethoxy, Phthalic acid, 1-Octadecene, Phenylacetaldehyde, 3-Octanone, Octanal, Methylheptenone and 2-Ethyl-1-hexyl alcohol. Conclusion: Overall, the results show that EPF could significantly reduce damage by O. longicollis and produce a wide profile of secondary metabolites. Further, analysis was used for principal components to determine whether separated classes of fungi can be distinguished from one another based on their metabolite profiles.