Lethal effect of ethanol on Solenopsis invicta Buren and economic fish

Abstract

The red imported fire ant (RIFA), Solenopsis invicta Buren, is an invasive pest species worldwide in many countries and regions. At present, its control mainly depends on synthetic insecticides. Although synthetic insecticides have the advantages of efficacy and convenience, their widespread use has a negative impact on the diversity of local arthropods. Ethanol is widely used as a disinfectant and has been consumed by people, but its insecticidal effect has not yet been evaluated. Here, the control effect of ethanol on the RIFA and its toxicity on four fish species were evaluated. The results exhibited that mortalities of all tested adult castes reached 100% after soaking in 70% v/v ethanol solution for one hour. All reproductive and worker pupae survived at 60% v/v ethanol treatment. In the soaking plus fumigation experiment, all adult castes and brood except female pupae were sensitive to 30% v/v ethanol solution. Conversely, female pupae showed the highest resistance to ethanol. More than 60% v/v ethanol concentration was needed to cause its 100% mortality. In the field experiment, 25% v/v and 50% v/v ethanol solution resulted in 70% and 80% reduction of mound 14 d after drench treatment, respectively. The ethanol vapour in the nest soil was higher than 80 ppm after 72 h of mound drench in the field with 25% v/v ethanol solution. Moreover, 30% v/v ethanol solution did not adversely affect the survival of four fish species exposed to the solution for a short time. This study suggests that mound drench can be alternatively employed with ethanol as a green organic solvent to control RIFA.