Are Metarhizium brunneum conidia transferred between male and female Agriotes obscurus adults?

Abstract

ABSTRACT The success of autodissemination of entomopathogenic fungi depends to some degree on the transmission of infective conidia or spores from contaminated hosts to conspecifics. In the present study, we examined the potential for direct transmission of a lethal dose of Metarhizium brunneum (Petch) conidia between opposite sex pairs of Agriotes obscurus L in the laboratory. Male and female beetles were exposed to M. brunneum conidia prior to pairing with an uncontaminated opposite sex partner (‘indirectly exposed’ to M. brunnneum), 2, 21 and 45 h after M. brunneum exposure. Ninety-six percent of the female beetles that had been exposed to M. brunneum granules died by day 15, as compared to 59% and 53% of the indirectly exposed and control females. From 15 days after the beginning of the experiment, females indirectly exposed to M. brunneum had higher odds of dying at any point in time than unexposed females across all post-exposure time periods. There was no significant difference in the odds of dying between indirectly exposed males and their unexposed counterparts at any point during the experiment. When the female beetle was exposed to M. brunneum forty-five hours prior to pairing, the pairs engaged in fewer courtship interactions relative to the other treatment groups, however less than 50% of all the pairs engaged in courtship interactions. The low incidence of courtship interactions and limited transfer of conidia between A. obscurus beetle pairs suggests that negligible horizontal transmission of M. brunneum conidia may occur between conspecifics.