Characterization and Biocontrol Potential of Fungal Isolates Associated with Eldana saccharina Walker (Lepidoptera: Pyralidae) in Sugarcane in Côte d'Ivoire

Abstract

Eldana saccharina Walker (Lepidoptera: Pyralidae) is the main stem borer of sugarcane and causes substantial economic losses in the sugarcane-growing areas of Côte d'Ivoire. This study, conducted at the Zuénoula integrated agricultural unit, aimed to identify the fungi naturally associated with E. saccharina larvae and to assess their potential as biological control agents. Larvae were collected from 39 plots and reared in the laboratory. Fungi were isolated from dead larvae, purified and identified on the basis of their macroscopic and microscopic characteristics. Twenty fungal isolates were obtained, of which 16 were assigned to four genera: Aspergillus, Fusarium, Trichoderma and Mucor. Aspergillus spp. were dominant (50 % of isolates), followed by Fusarium spp. (20 %). Fusarium isolates showed similar mycelial growth on potato dextrose agar (PDA) and Czapek-glucose agar (CGA), with identical growth rates (about 1.2 cm day−1). Sporulation peaked on day 14 of incubation and was significantly higher in potato dextrose liquid (PDL) medium than in Czapek-glucose liquid (CGL) medium (7.05 × 106 versus 3.39 × 106 spores mL−1). Fusaric acid production was confirmed by spectrophotometry, with higher concentrations on CGA medium (mean 3.6 mg mL−1) than on PDA (3.1 mg mL−1); however, toxin content decreased progressively with incubation time. These results indicate that several fungi are naturally associated with E. saccharina larvae. Fusarium spp. are of particular interest for future biological control applications owing to their production of fusaric acid, a toxic metabolite whose accumulation dynamics remain to be controlled.