Paraben preservatives do not affect bait transport behavior of Solenopsis invicta and control effectiveness of indoxacarb bait

Baiting is one of the main methods for controlling red imported fire ants (Solenopsis invicta). However, commercial fire ant baits contain large amounts of lipids that may cause microbial contamination, leading to active-ingredient degradation and palatability reduction.

Adding lipid-soluble preservatives may reduce production costs associated with the sterilization processes of fire ant bait and extend product shelf life during storage and field application by inhibiting microbial proliferation. This study hypothesized that the three lipid-soluble paraben preservatives (methylparaben, propylparaben, and butylparaben) would not adversely affect palatability and effectiveness of fire ant baits. Field multiple-choice tests were conducted to compare bait transport amounts of S. invicta responding to bait containing each preservative (at concentrations of 0.05%, 0.1%, or 0.2% in soybean oil) and control baits.

Results showed no significant differences in transportation among preservative-treated and control bait (the amounts of baits transported containing each preservative concentration showed no significant difference from the control). Laboratory bioassays were then conducted to evaluate the effectiveness of 0.1% indoxacarb baits with/without preservatives.Mortality and median lethal time (LT₅₀) of fire ants were not significantly different among 0.1% indoxacarb baits containing preservative or not, indicating the absence of antagonistic effects between preservatives and the active ingredient.

This study demonstrates the applicability of these three lipid-soluble paraben preservatives in fire ant bait production.