Effect of endophytic colonization of cotton plants by Beauveria bassiana on the survival and damage of Helicoverpa armigera and Haritalodes derogata

Background Beauveria bassiana (Balsamo) Vuillemin is a fungal entomopathogen that can colonize plant species endophytically. As an endophyte, B. bassiana may play a key role in the natural protection of crops against insect pests and their damage. This study assessed the effect of the endophytic colonization of cotton by Beauveria bassiana on larval survival and feeding damage caused by Helicoverpa armigera Hübner and Haritalodes (= Syllepte ) derogata Fabricius caterpillars. Cotton plants were inoculated with B. bassiana conidia using two methods: seed coating before sowing and foliar spraying. Three isolates of B. bassiana Bb11, Bb3, Bb115, at a concentration of 10 8 conidia/ml each, were used. Control treatment consisted of plants treated with 0.05% sterilized tween 80 solution without fungal conidia. The experimental design consisted of a randomized complete block design with four treatments, namely 3 B. bassiana isolates (Bb11, Bb3 and Bb115) and an untreated control, with fifteen (15) replicates (plants) per treatment and per pest species. Endophytic colonization of leaves, stems, roots, flowers and bolls was assessed four times during the cotton development cycle using culture-based detection on PDA medium. Results Endophytic colonisation by B. bassiana was detected in multiple cotton organs following both seed-coating and foliar-spraying inoculation, although colonisation patterns varied among isolates and organs. The mean number of leaves damaged by H. derogata was lowest 8 days after infestation with Bb3-inoculated plants (1.30 ± 0.20 leaves per plant, foliar spraying), while overall larval survival was lowest with Bb11 via seed coating (11.46%) and Bb3 via foliar spraying (10.43%). The percentage of flowers damaged by H. armigera was lowest with Bb3 (3.26%, foliar spraying), and overall H. armigera larval survival was also lowest with Bb3, regardless of inoculation technique. Conclusions These findings show a significant effect of the endophytic colonization of cotton crop on feeding and survival of H. derogata and H. armigera larvae. This suggests that endophytic B. bassiana has potential as a component of integrated cotton pest management in Benin, although field validation is required.