The Temporal and Spatial Invasion Genetics of the Western Corn Rootworm (Coleoptera: Chrysomelidae) in Southern Europe

Abstract

This study describes the genetics of the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte in southern Europe during the introduction (1996–2001) and establishment/spread (2002–2011) phases of its invasion. The Diabrotica microsatellite core-set was used to perform traditional population genetics analyses. Our results indicated that during the introduction phase genetic diversity and population genetic structure were lower overall as compared to the establishment/spread phase. Unusually high genetic differentiation was found between the Italy and southern Europe comparisons, including high differentiation between Italian populations separated by a short distance during the establishment/spread phase. STRUCTURE analysis revealed two genetic clusters during the introduction phase and two genetic clusters during the establishment/spread phase. However, bottlenecked populations were only detected during the invasion phase. A small but significant isolation by distance effect was noted in both phases. Serbia was the geographic source of WCR to Croatia and Hungary in the introduction phase, while the United States of America was the possible source of WCR to Italy in 2001. These introductory populations were the subsequent source of individuals sampled during the establishment/spread phase. Repeated introductions and admixture events in southern Europe may have resulted in genetically diverse WCR populations that have attained 83% of all known alleles worldwide.

Two Decades of Invasive Western Corn Rootworm Population Monitoring in Croatia

“…However, this may have been due to the intensive monitoring program in Croatia during the study period [50]. The results confirmed the original finding that allelic richness during the introduction phase was low but consistent throughout all Southern European populations [55]. However, during the establishment and spread phases of the invasion process, allelic richness was higher for all Southern European populations.…”

“…Bayesian cluster analysis revealed two genetic clusters that joined the WCR from Croatia and Serbia, but separated them from U.S. populations. These clusters showed that numerous U.S. individuals had both European and U.S. ancestry, which suggests the existence of bidirectional gene flow [55]. Bottlenecks were identified within all Croatian populations sampled in 1996 and 2011 and only two populations in 2009.…”

“…More recently, the population genetics of WCR in Southern Europe during all invasive phases (introduction, establishment, and spread) were investigated [55]. Results from the study showed that during the first phase (introduction), the number of observed alleles was low (19–27; 45%) in Southern Europe compared to suspected source populations from the U.S. (Iowa or Illinois).…”

Characterization of pyrethroid resistance in the western corn rootwormDiabrotica virgifera virgiferaLeConte

“…For over a century, the WCR was primarily confined to North America with its center of origin believed to be in Central America (Webster 1895, Krysan 1982, Lombaert et al 2018. However, in 1992 it was found in Serbia, and has been spreading through Europe since then (Berger 2001, Miller et al 2005, Wesseler and Fall 2010, Lemic et al 2015, Mrganić et al 2018).…”

“…This insect pest also became a major concern for European countries after it was first found in 1992 close to Surcin International Airport in Belgrade (Berger 2001, Miller et al 2005). Since this first report, WCR has spread to more than 15 countries in Europe and has placed many others at risk of biological invasion (Aragón et al 2010, Wesseler and Fall 2010, Lemic et al 2015, Mrganić et al 2018.…”