Genetic and phenotypic effects of hybridization in independently introduced populations of the invasive maize pest Diabrotica virgifera virgifera in Europe.
The North American western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) was introduced into Europe several times during the end of the 20th century. Outbreaks in north-western Italy (NW Italian) and central and south-Eastern Europe (CSE European) have merged in 2008 and insects interbreed since then. This study compared the genetic diversity (multi-locus genotype analyses at 13 microsatellites markers) and ten phenotypic traits among the CSE European and NW Italian populations as well as their hybrid offspring. All insects were reared under standardised laboratory conditions. Neutral genetic polymorphism appeared moderate in parental and hybrid populations, compared to North American populations. Some increase in neutral genetic variability was detected in the hybrids' expected heterozygosity and allelic richness compared to parental populations when family structures were considered. In 70% of the assessed phenotypic traits, the population type (CSE European, NW Italian, hybrids) influenced a trait, but averages in hybrids never exceeded those in their parents. Population type did not influence fecundity or adult lifespan (reflecting fitness) and not the proportion of adults flying (reflecting dispersal capabilities). There was no evidence yet that hybridization influences variability of phenotypic traits. In conclusion, there are only few indications that hybrids between the two overlapping invading European populations may in the longer term, take advantage through higher neutral genetic diversity and subsequent phenotypic adaptability.