Beauveria bassiana for the control of leafcutter ants: strain and host differences

Abstract

Leafcutter ants are a serious pest for forestry plantations and crops in Latin America. They have been traditionally controlled using chemical synthetic pesticides, which are known to have many negative effects to non-target organisms and the environment. Therefore, there is an urgent need for the development of alternative strategies of control, among which the biological control using fungal pathogens is a promising one. We evaluated in laboratory 3 strains of Beauveria bassiana (B5, B6, B7) against workers from 4 to 7 field colonies from 5 species of Acromyrmex leafcutter ant species which are considered pests in the region. Our results showed that all strains were pathogenic, although there are some ant species that turned out to be more susceptible either due to their intrinsic immunity or the natural load of pathogens they carried. The three strains were similarly effective for 3 of the 5 species, A. ambiguus, A. crassispinus, and A. lundii, being responsible for more than 80% of their mortality overriding the effect of their natural pathogens. Only strain B6 was able to kill a similar percentage of ants of A. heyeri, and strain B7 half of them. B5 in A. heyeri, as well as all three strains in A. lobicornis, were responsible for up to 30% of the mortality, but with the additive effect of the pathogens naturally brought by these ants accounted for a 70% of their mortality. We recommend using B6 to test the control of Acromyrmex leaf-cutting ants in the field.