Delayed Toxicity of Fast Acting Fire Ant Baits

Mentor: David Oi

Abstract:   The objective of this study was to determine the delayed toxicity of active ingredients in fire ant baits.  Delayed toxicity was defined as an active ingredient that produced less than 15% mortality by 24h and greater than 89% mortality at the conclusion of a 14-day study.  Delayed toxicity is an important factor in fire ant baits because the delay in death enables the active ingredient to be spread throughout a fire ant colony.  Hydramethylnon has been the standard active ingredient in fire ant baits for many years.  Spinosad is a newer active ingredient that claims to be faster acting than hydramethylnon.  Indoxacarb is an active ingredient that is currently unregistered but is reportedly fast-acting.  To assess delayed toxicity, red imported fire ants, Solenopsis invicta, were exposed to each of these active ingredients for 24h, and mortality readings were taken at set intervals within a 14-day test period.  Hydramethylnon was the only bait that approached the criteria for delayed toxicity, showing less than 15% mortality by 20h and 89% mortality by Day 8.  Spinosad and indoxacarb acted too quickly, with 90% and 57% mortality by 24h, respectively.  However, research conducted previously showed that indoxacarb produced 100% mortality of large laboratory colonies in 3 days.  These data suggest that the criteria for delayed toxicity may have to be altered to accommodate the new, faster-acting fire ant baits.

Melissa making friends with fire ants.