Successful establishment of the invasive fire ant Solenopsis invicta in Taiwan: insights into interactions of alternate social forms


*Cheng-Jen Shih, Department of Entomology, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 106, Taiwan.


Aim  Understanding the factors underlying the successful establishment of invasive ant species is critical for developing quarantine strategies to prevent additional invasions as well as for determining how such species overcome the selective pressures in invaded areas. Although several studies have revealed differences in the social organization and population genetics of invasive ants in their native and introduced ranges, few studies have considered the potential interactions between alternate social forms within newly-invaded areas simply because many invasive ants are characterized as polygyne or unicolonial.

Location  Taoyuan and Chiayi County, Taiwan.

Methods  Both social forms (polygyne and monogyne) of the red imported fire ant, Solenopsis invicta, occur in two separately invaded areas in Taiwan (Taoyuan and Chiayi). We employed intensive sampling methods and diagnostic polymerase chain reaction assays to determine the distribution of these two social forms in both infested areas in Taiwan.

Results  The distribution of social forms differs dramatically between the two infested areas, consistent with different invasion histories regarding the original make-up of individuals comprising the initial founder group. The Taoyuan population likely was colonized initially by ants of both social forms, with the subsequent spread characterized by continuous outward movement of the two forms, particularly the monogyne form. In contrast, the initial founders of the Chiayi population likely were of the polygyne social form only, suggesting the monogyne social form in this population appeared only recently and likely arose directly from polygyne queens converting to the alternate social form.

Main conclusions  Our results provide detailed insights into the invasion history of S. invicta in Taiwan and suggest that the distinct reproductive biology of the two social forms may have shaped the current distribution of S. invicta in these infested areas and that the dynamics of two forms may affect the long-term persistence and potential for spread of this pest ant species.