Map of sampling locations for Rhipicephalus microplus ticks in southern Texas. The tick eradication quarantine area (TEQA) lies between the international border between Texas and Mexico (the Rio Grande River) and the pink line. This genetic study used 63 tick collections made at 46 properties during 2005–2010 (see Table 1 for sample sizes and dates of collection). Each location is color-coded to represent the four main genetic groups (see Additional file 3: Figure S1) that were found with Bayesian assignment testing using STRUCTURE software . The light blue symbols represent highly admixed collections along the Rio Grande River that do not assign to any single genetic group. The green group in eastern Zapata Co. (Rm20-Rm32) includes pyrethroid-resistant tick collections. The two temporary preventative quarantine areas (TPQAs or blanket quarantine zones) represented by light green polygons were enforced during 2007–2012 to address new infestations outside of the TEQA; the maximum extent of these TPQAs is shown (year 2009). The blue triangles from the inset map mark three livestock feedyards where traceback ticks from Prop37 (Rm43) were transported in April of 2008 and later eradicated.