Response of Solenopsis invicta Workers to Polyoxyethylene Tridecyl Ether Surfactants in Relation to Hydrophilic-lipophilic Balance

Surfactants are commonly used in insecticide formulations as adjuvants to enhance the performance of the insecticidal active ingredients. However, surfactants may have their own intrinsic detrimental effect on insects. In this study, the responses of red imported fire ants, Solenopsis invicta Buren, to 6 polyoxyethylene tridecyl ether surfactants (Ethal TDA) and their relationships to the hydrophilic-lipophilic balance (HLB) numbers were investigated in topical, glass-vial and immersing bioassays. In topical and glass-vial bioassays, significant linear dependence of ant mortality on HLB number was detected and the mortality was negatively related to HLB number. In immersing bioassay, a fast immobilizing effect was observed; however, the time needed to immobilize ants was not related to HLB number in most cases. In conclusion, Ethal TDA surfactants have intrinsic toxicity against S. invicta workers and ant mortality in both topical and glass-vial bioassays was negatively related to their HLB numbers.