Control of Argentine Ants (Hymenoptera: Formicidae) in Citrus using Methoprene and Imidacloprid Delivered in Liquid Bait Stations

Les Greenberg, Kristen E. Tollerup, Michael K. Rust


We conducted trials in a citrus grove infested with Argentine ants [Linepithema humile (Mayr); Hymenoptera: Formicidae] using bait stations (9.8 per ha) filled with bait consisting of either 0.001% imidacloprid as one treatment or 0.25% methoprene as a second treatment. The 2 treated areas and a control were widely separated in the grove. Within each area, trees were randomly selected to receive sucrose water monitors. Consumption of the sucrose water is a measurement of ant foraging activity that we used to compare treatments and the control. For all weekly samples except one, consumption by ants in the imidacloprid-treated area was significantly lower than in the controls. The methoprene treatments gave a more complex outcome: the consumption of the bait was significantly higher than in the controls during wk 5 and 8, but then rapidly descended below the consumption level of the control during wk 11 and 12. A post-experimental examination of the control and methoprene areas showed that queen numbers in the methoprene area were 93% lower than in the control area. A subsequent laboratory experiment comparing the methoprene bait in sucrose to sucrose only showed significant worker mortality after 9, 12, and 16 wk, while at the end of the experiment queen mortality was 24% higher than in the controls (ns). The initial rise in field ant numbers with the methoprene bait would pose a problem for its use by growers unless it would be used early in the season before hot weather would drive the annual increase in ant numbers.

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