Boric acid, imidacloprid, and thiamethoxam in sucrose aqueous baits had different delayed toxicities to worker Argentine ants, Linepithema humile (Mayr). The concentrations required to produce an LT₅₀ (time required to produce 50% mortality) within 1–4 d were 3.63–0.55% boric acid, 9.2 × 10⁻³ to 7.1 × 10⁻⁴% imidacloprid, and 3 × 10⁻⁴ to 2 × 10⁻⁵% thiamethoxam. The three toxicants were not repellent. Other laboratory trials showed that 1% boric acid, 5 × 10⁻⁴ to 5 × 10⁻³% imidacloprid, and 1 × 10⁻⁵ to 1 × 10⁻³% thiamethoxam had delayed toxic effects, whereas 0.5% boric acid and <5 × 10⁻³% imidacloprid did not. Baits that provided an LT₅₀ between days 1 and 4 were considered to have delayed toxic effects. The utility of aqueous sucrose baits and toxicants soluble in such systems and the negative impact of fast-acting toxicants on trail following, recruitment, trophallaxis, and control of Argentine ants are discussed.