Outbreaks of cockchafers – how do genetic population structures of Melolontha melolontha and M. hippocastani differ?

Abstract Cockchafers Melolontha spp. are polyphagous root pests and outbreak species of considerable economic importance to forestry in Europe. However, knowledge about genetic diversity among and between populations of cockchafers is far from sufficient. In this study, we fill several gaps in the knowledge of genetic population structure and the intensity of gene flow between Melolontha melolontha ( Mm ) and M. hippocastani ( Mh ). Specifically, we used microsatellite markers of 421 imagines from three main outbreak areas in Poland. Our study revealed some differences in polymorphism and population structuration between the two species. Mm was characterized by higher polymorphism and some evidence of population structure, while Mh did not show population structuring, which may indicate that these two species have undergone different historical events. It is likely that only Mm experienced a reduction in population size but both species currently have high effective population sizes - likely as a result of an ongoing outbreak. A number of ~ 10 migrants per generation allows gene flow and maintains equilibrium in the population. Our study also revealed some important differences in migratory behavior between the sexes, with male cockchafers making more frequent long-distance flights. Current ecological and anthropogenic changes that alter the quantity and quality of the food base appear to favor the fecundity, development and dispersal of cockchafers. Our study adds cockchafers to the list of outbreak species with available genetic information. This information can be an important component of effective management strategies and a foundation for understanding and predicting the evolution of these species.