Use of liquid nitrogen to treat solenopsis invicta (Hymenoptera: Formicidae) nests

Liquid nitrogen (LN2) injection was used to against the red imported fire ant (Solenopsis invicta Buren) by taking the advantage of rapid killing, no side effects from residuals, and non-dependence on weather conditions of this method. Red imported fire ants workers were placed in glass bottles and treated by sub-zero temperatures for either two or zero minutes after thermo-equilibrium to determine the lethal low temperature. Fire ant nests were then treated by LN2 and the survival of the ants was monitored. Thus-15 °C was shown to cause 100% of mortality of workers at 24 hours post treatment. Large numbers of ant corpses, which included larvae, pupae and queens, were discovered in the nest after LN2 treatment. In a field experiment, 10 nests were treated by LN2, while 9 were left as controls. The number of active nests significantly decreased to just one nest at the 14th day post LN2 application and none was considered to be functional at the 21st day. These results suggest that LN2 freezing is capable of eliminating individual fire ant nests effectively, and that this treatment is useful for areas of high human activity and for agricultural and other areas that have a low tolerance to conventional pesticides.