New lethal liquid bait for control of pest ants

An aqueous ant bait consisting of sucrose (4.55% w/v), essential amino acids (EAAs, 1%), and water is known to be highly appealing to multiple ant species throughout the foraging season. Here, we tested whether this bait, combined with boric acid as the lethal agent, has potential for control of pest ants. Specifically, we: (1) assessed bait lethality to diverse species of ants (European fire ants, Myrmica rubra, western carpenter ants, Camponotus modoc, thatching ants, Formica oreas); (2) tested the effect of boric acid concentration on mortality of M. rubra workers and colonies; (3) compared consumption, and demise timeline, of lethal liquid baits and lethal gel baits; and (4) investigated whether lethal liquid baits reduce the size of M. rubra colonies. In laboratory experiments, the bait induced rapid worker mortality (< 22 days) in all three species of ants tested. Increasing the concentration of boric acid from 1% to 5.4% accelerated the demise of only worker ants, but not queen ants, in M. rubra colonies, indicating that 1% boric acid is sufficiently lethal. Worker ants of M. rubra strongly preferred liquid baits to gel baits of identical nutrient composition, with the former bait accelerating worker demise. In a field experiment in a public park heavily infested with M. rubra, the 12 treatment colonies provided with a lethal liquid bait (4.55% sucrose; 1% EAAs; 1% boric acid) over 114 days significantly declined, whereas the 12 control colonies provided with the corresponding non-lethal bait did not. The bait, with appropriately adapted bait deployment protocol, should be tested for control of other pest ants, particularly those that preferentially feed on liquid foods.