Assessment of different methodologies for evaluating the virulence of biological agents against fire ants (Solenopsis spp.) under laboratory conditions

ABSTRACT The genus Solenopsis, commonly known as fire ants, includes 196 species. These ants are considered pests due to the damage they cause in urban areas and agricultural systems. Their painful stingers hinder manual harvesting, and they feed on crops and engage in mutualistic interactions with aphids. As a result, there is considerable interest in identifying biological control agents and developing effective laboratory methods for evaluating their virulence. Such efforts are hindered by the fact that most available methodologies were originally designed for chemical insecticides. This study aimed to evaluate six different laboratory methodologies for testing the virulence of biological agents against Solenopsis spp. The tested approaches were: spraying water into trays with approximately 35 worker ants; pipetting water into containers with 30 worker ants; spraying water into containers with 30 worker ants; using a Potter spray tower to apply water, and treat containers with 30 workers; pipetting water onto distinct developmental stages of ants in Petri dishes; and applying water to microcolonies in Petri dishes. Additionally, various concentrations of culture media were assessed to determine their suitability for bacterial assays. Among the methods tested, the last two mentioned approaches presented fewer logistical challenges and were more likely to generate reliable data for fire ant control. The 25% Luria-Bertani medium was associated with the lowest worker mortality and is recommended as a negative control in bacterial experiments.