Effects of red imported fire ant baits on some non-target ants

Abstract

Laboratory tests were conducted to determine the effects of one-time baiting with commercially formulated red imported fire ant (RIFA) baits on worker mortality, egg production, and brood ranking of two non-target, competitor ant species and two pest ant species. The non-target ants included the thief ant, Solenopsis (Diplorhoptrum) molesta (Say) and the little black ant, Monomorium minimum (Buckley). The pest ant species included the RIFA, Solenopsis invicta (Buren) and the pharaoh ant, Monomorium pharaonis (Linnaeus). The former two species were each tested with a metabolic inhibitor, Amdro® and an insect growth regulator, Logic®, whereas the latter two species were tested with two metabolic inhibitors, Amdro® and Combat®, and two insect growth regulators, Logic® and Distance®. Laboratory data indicated that toxic baits, as well as control and regular laboratory diet, elicited similar recruitment rates in all the tested species. Further, there was no significant difference in the amount removed in 24 hours for any of the chemical baits. Evaluation of bait effects on worker mortality, egg production, and brood ranking for a period of two months indicated detrimental effects of all the toxic baits against the two non-target species. The metabolic inhibitors, Amdro® and Combat® acted similarly and caused maximum effect on worker mortality. In addition, they caused mortality to queens, reduction in egg production, and decrease in brood amounts in treated colonies of all the tested ant species. The insect growth regulators, Logic® and Distance®, on the other hand, showed maximum effect on reduction of egg production and brood mortality, while showing some amount of worker mortality. Control colonies and those fed with regular laboratory diet, on the other hand, did not show any signs of unhealthiness or unnatural mortality for any of the species, and continued to grow during the two months observation period. Results of the laboratory tests indicated that Monomorium minimum and Solenopsis (Diplorhoptrum) molesta, two important competitor ant species identified for natural suppression of RIFA populations, are negatively affected by toxic baits that are meant specifically for the control of the RIFA.