Combining the virulent Beauveria bassiana (Balsam) Vuillemin LCB289 and nematode strains to control pupae of Ceratitis capitata Wiedemann

Abstract

ABSTRACT Entomopathogenic fungi (EF) and nematodes (EPN) can infect pupae of C. capitata Wiedemann in the soil, where they are protected from most control measures. This study evaluated infective juvenile (IJs) density to achieve high control efficiency, the residual effect of commercial strains of Heterorhabitidis bacteriophora (Poinar) and Steinernema carpocapsae (Weiser), and their combined application with Beauveria bassiana (Balsam) Vuillemin LCB289 on pupae mortality. Applying 106 IJs m−2 of both EPN species to columns with sandy Yellow Ultsol at laboratory temperature (24.0 ± 2°C) caused pupae mortality higher than 80%. Probit analysis showed that the curves for the EPN species had statistically similar slopes, with LC50 of 3.57 × 106 for H. bacteriophora and 2.12 × 106 for S. carpocapsae. The former showed a median potency 36% higher than H. bacteriophora. Microscope observations showed that infection by both species resulted in the melanization of pupae and no visual differences in the EPN growth in the cadavers. In a long-term experiment in greenhouse conditions (T = 26.5 ± 4.2°C; Ru = 62.7% ± 22.5), a single application of S. carpocapsae in columns with sandy Ultisol showed a residual effect of 21 days, while for H. bacteriophora it was lower than 15 days. Concomitant application of S. carpocapsae and the virulent EF strain B. bassiana LCB289 in columns with sandy soil in a greenhouse experiment in the same conditions (T = 26.5 ± 4.2°C; Ru = 68.5% ± 23.3) increased the median potency of the BCAs, resulting in a lower lethal concentration applied (LC50).