Using population genetics approaches to trace the origin of the USA invasion of the whitefly Bemisia tabaci biotype Q

Whiteflies in the sibling species group Bemisia tabaci (Hemiptera: Aleyrodidae) are among the world’s worst invasive pests, causing serious economic losses in the agricultural industry. For example, the introduction of an invasive variant (biotype B) in the USA in the 1990’s resulted in more than $1 billion in damage to crops. Another invasive variant, biotype Q, indigenous in the Mediterranean, was first detected in the state of Arizona in 2004 and a nationwide survey has since confirmed its presence in 25 states. The aim of our study was to trace the introduction history of this biotype in the USA by comparing samples collected from 8 states in 2005 to potential source populations sampled across the Mediterranean. We assessed genetic variation in 8 microsatellites and analyzed data in a Bayesian framework to infer the sources of this invasion and routes of dispersal across states. We also analyzed mitochondrial cytochrome oxidase I (COI) gene sequences using a statistical parsimony network. Our results suggest that the introduced populations originated from both Eastern and Western Mediterranean sources, probably as a result of independent invasions. Using Approximate Bayesian Computation approaches we show that whiteflies originating from the Western Mediterranean most likely spread through California in separate colonization events, probably via transport of infested poinsettias. These results are relevant to monitoring B. tabaci and other insect pest and vector invasions, and broaden our understanding of how insects travel on plant material through international corridors, spread from the initial sites of introduction, and colonize new habitats.