Beauveria bassiana (Balsamo) Vuillemin (Deuteromycetes) applied to laboratory colonies of Solenopsis invicta Buren (Hymenoptera: Formicidae) in soil

Laboratory experiments were done to evaluate effects of a Beauveria bassiana (Balsamo) Vuillemin. strain on Brazilian and American populations of Solenopsis invicta Buren. Three application methods used for treatment of fire ants were sprinkling material on the soil surface, injection into the nest, and mixing conidia into soil. Two hundred grams of B. bassiana-rice material was applied on colonies with approximately 7 g of ants in plastic pots with nest soil. Mortality of ants treated with B. bassiana and infection of cadavers were significantly higher than in the control during the first 3 wk of the experiments in the United States and in Brazil. No differences were observed in susceptibility of the S. invicta populations to B. bassiana strain 447 or in the effects of soil on the performance of the fungus. A maximum 70% reduction of the population occurred when colonies with 3 g of ants in 300 g of soil were injected with 0.3 g of a powder formulation containing 50% of B. bassiana conidia. In large colonies with approximately 10,000 ants, application of 25 g of formulation (1 part conidia:4 parts diatomaceous earth) by injection into nest or surface treatment caused ant mortality of between 70 and 92%. Application of fungus by mixing conidia into soil did not cause significant mortality of ants. Injection of powder formulation of B. bassiana can be advantageous because better fungus-host contact occurs and lower doses are required