δ²H of Japanese beetles during a 5-week experiment in which beetles from Virginia were reared in terracosms with plant material and environmental water from Oregon.

<p>Symbols show means and bars two standard errors. Whole-body tissue samples were analyzed each week (circles), whereas wings (squares) and elytra (triangles) were sampled in week 0 and week 5.</p

Map of continental US showing the status of the Japanese beetle invasion, by county: well established (red), establishing (orange), occurrences reported (yellow), and no occurrences known (white).

<p>Black circles indicate sites of beetle collections used to develop the relationship between beetle and precipitation δ²H values, and the star indicates the study site at the Portland International Airport. Data compiled from refs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149599#pone.0149599.ref015" target="_blank">15</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149599#pone.0149599.ref019" target="_blank">19</a>, as described in the Methods (<b><i>Potential Sources of Origin)</i>.</b></p

δ²H of Japanese beetles collected at the Portland International Airport (Oregon, USA) (circles) and in locations nearby (triangles) from 2006–2013.

<p>Increased trap densities around the airport have increased the probability of catching beetles as they fly from planes.</p

Estimated days between arrival and capture of each individual beetle captured at the Portland International Airport (open circles) and the average for each year (blue squares, with bars showing 95% confidence intervals; note year with combined data).

<p>The solid line shows the exponential fit for the temporal relationship.</p