The odorous house ant (Tapinoma sessile) is an adaptive and widespread pest ant species
found in North America. Despite the economic and ecological impact of pest ants, effective
management still faces many challenges and control failures with liquid spray insecticides in urban
and natural environments. In many insects such as bed bugs and cockroaches, chemical control
measures have resulted in insecticide resistance. However, in contrast to non-social insects,
insecticide resistance has never been documented in social insects. The current study had three
main goals. The first objective was to examine regional variation in T. sessile insecticide
susceptibility to three classes of insecticides commonly used in urban ant control. The second
objective was to compare insecticide susceptibility in T. sessile colonies collected in natural vs.
urban areas. The final objective was to determine if insecticide susceptibility varies in workers vs.
queens. A total of 30 T. sessile colonies were collected within a 50-mile radius of Purdue
University campus, Tippecanoe County, Indiana. Fifteen colonies were collected in natural areas
and 15 in urban areas. Insecticide susceptibility of all 30 colonies was tested using residual
exposure assays. Urban and natural colonies showed no significant differences in tests with
lambda-cyhalothrin and fipronil. In tests with dinotefuran, urban colonies were significantly more
tolerant relative to natural colonies. These results suggest that habitat type does not reliably predict
susceptibility levels in individual populations. Queens were found to be significantly more tolerant
relative to their worker counterparts across all three insecticides. Lower insecticide susceptibility
in the queens may explain why T. sessile is such a persistent pest in urban environments. This
15
study’s results can in part provide a foundation for the development of more effective and efficient
control methods for T. sessile.