Biological control of leaf‐cutter ants using pathogenic fungi: experimental laboratory and field studies

Abstract

AbstractThe alternative use of biological control agents (BCAs) against leaf‐cutter ants (LCAs) is in increasingly high demand due to the negative consequences of traditional pesticides. Regarding LCAs, BCAs include entomopathogens that infect them, and mycopathogens that kill the fungi cultivated by these ants. The simultaneous use of multiple BCAs requires that the agents do not negatively affect each other. To test this hypothesis, we set up laboratory assays to evaluate in vitro interactions among an entomopathogen [Beauveria bassiana (Bals.‐Criv.) Vuill.], a mycopathogen [Trichoderma virens (JH Mill., Giddens & AA Foster) Arx], and the LCA‐cultivated symbiotic fungus Leucoagaricus sp. We also tested the BCAs in the field by offering them in three types of bait to Acromyrmex lundii Guérin‐Méneville (Hymenoptera: Formicidae), in order to evaluate: (1) the control efficiency of these BCAs on LCA field colonies, and (2) whether there was delayed rejection of baits placed sequentially. Our in vitro results showed that T. virens was not affected by Leucoagaricus sp. or by B. bassiana, whereas B. bassiana was negatively affected by the mycopathogen and the cultivated fungus, probably due to substrate competition. Leucoagaricus sp. was not affected by B. bassiana but it was negatively affected by T. virens, as predicted, destroying the cell walls of the cultivated fungus. The field study showed 62.5% control of LCA after applying the three types of bait on three occasions throughout 27 weeks, without detecting any delayed rejection effect. Due to the variability registered in colony inactivity, we propose a continued inactivity of 13 weeks as a criterion for A. lundii control. We discuss the importance of continuous long‐term assessments of BCAs on LCA control.