Improving ecological fitness of Beauveria bassiana conidia to control the sugar cane borer Diatraea saccharalis

Abstract

ABSTRACTDiatraea species are considered the most important insect pests in sugarcane crops in Colombia and other South America countries. Previous research demonstrated Beauveria bassiana isolate Bv062 to be pathogenic to larvae of Diatraea species under laboratory conditions. However, virulence of the isolate was variable, possibly affected by inoculum quality. The aim of this research was to select an appropriate mass culture medium to produce conidia with consistently high yield, high virulence, and high storage stability. Conidia were produced on three semi-solid media based on rice, oat and potato, which were adjusted to three levels of water activity (aw). Conidia yield, germination, polyols accumulation, enzymatic activity, and virulence to Diatraea saccharalis larvae, before and after 30 days of storage at 30°C, were measured. Conidia produced on potato-based medium were the most virulent, with a median lethal time (LT50) of 8.9 days, compared to 9.7 and 9.1 days for rice and oat media, respectively. Insecticidal activity was stable after one month of storage for conidia produced on potato (LT50 8.0 days) but was reduced for conidia produced on the other media (LT50 13.0 days and 11.7 days for rice and oat, respectively). Mannitol was the predominant polyol in conidia and trehalose was not detected. Maximum yield and storage stability were obtained in the potato-based medium (C:N ratio of 30:1). Based on these results, potato-based medium is superior to the standard rice-based medium for the production of B. bassiana Bv062 conidia with better ecophysiological performance to control the sugar cane borer.