Bait distribution among multiple colonies of Pharaoh ants (Hymenoptera : Formicidae)

Pharaoh ant, Monomorium pharaonis (L.), infestations often consist of sever al colonies located at different nest sites. To achieve control, it is desi rable to suppress or eliminate the populations of a majority of these colon ies. We compared the trophallactic distribution and efficacy of two ant bai ts, with different modes of action, among groups of four colonies of Pharao h ants. Baits contained either the metabolic-inhibiting active ingredient h ydramethylnon or the insect growth regulator (IGR) pyriproxyfen. Within 3 w k, the hydramethylnon bait reduced worker and brood populations br at least 80%, and queen reductions ranged between 73 and 100%, when nests were in p roximity (within 132 cm) to the bait source. However, these nest sites were reoccupied by ants from other colonies located further from the bait sourc e. The pyriproxyfen bait was distributed more thoroughly to all nest locati ons with worker populations gradually declining bq 73% at all nest sites af ter 8 wk. Average queen reductions ranged from 31 to 49% for all nest sites throughout the study. Even though some queens survived, brood reductions w ere rapid in the pyriprosyfen treatment, with reductions of 95% at all loca tions by week 3. Unlike the metabolic inhibitor; the IGR did not kill adult worker ants quickly, thus, more surviving worker ants were available to di stribute the bait to all colonies located at different nest sites. Thus, fr om a single bait source, the slow-acting bait toxicant provided gradual, Li lt long-term control, whereas the fast-acting bait toxicant provided rapid, localized control for a shorter duration.