Desiccation resistance in populations of the red imported fire ant (Hymenoptera: Formicidae)

Abstract

The red imported fire ant, Solenopsis invicta Buren, is rapidly expanding its range throughout Texas and is even surviving in areas once thought inhospitable. Therefore, the objective of this study was to determine if populations of red imported fire ants from western Texas are more resistant to desiccation than are those from eastern Texas. Colonies were sampled from 6 different locations on a southeast to northwest transect through Texas. Minor workers from each location were subjected to low humidity, and the mean LT50s from among locations were compared to determine differences in desiccation tolerance among populations. Results show that the LT50 of minor workers collected in far northwestern Texas is ≃7 h; whereas, that of minor workers from far southeastern Texas is significantly less (P < 0.05) at ≃5.5 h. In addition, these LT50s are significantly different (P < 0.05) from the other 4 locations sampled from the middle of the transect. Therefore, workers from western Texas (xeric conditions) are less prone to desiccation than are those from far eastern Texas (moist conditions) even though minor workers tested from eastern Texas were significantly larger than all others along the transect. There results indicate that the red imported fire ant may be able to adapt and expand its range at a rate faster than initially suggested.