Population structure of the potato tuberworm Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae) in the United States

The potato tuberworm is considered one of the most damaging insect pests of potatoes worldwide. Although tuberworm was recorded in California as early as 1856, it was first reported in damaging numbers in Oregon and Washington State in the early 2000’s. The objective of this study was to determine the population structure of PTW to understand the potential origin of emerging PTW populations in the Western United States. PTW adults were collected from potato fields in major potato production regions in the North-Western, South-Central and North-Eastern United States. AFLP were used to determine genetic differentiation among PTW from different presumed populations. We found geographically based population structure across the United States. There was a North-Western, a South Central and a North-Eastern sub-population. Posteriors probabilities in structure confirmed the existence of three clusters. The three clusters present in the data corresponded with the geographic origin of most of the sampled PTW. Thus, macrogeographically, tuberworm in the US is subdivided in three defined sub-populations. The Appalachian Mountains could be acting as a geographic barrier isolating Easter from Western PTW sub-populations. Similarly, the Rocky Mountains could be isolating the North-Western and South-Central PTW populations. Alternatively, genetic isolation by distance may also explain the population structure found in the US PTW populations. Our data provide baseline data for the molecular characterization of tuberworm populations which will enable us to track the origin of future invasions.