Illinois Natural History Survey Champaign, Illinois
A coherent understanding of adult western corn rootworm, Diabrotica virgifera virgifera LeConte, movement ecology has remained elusive because of conflicting evidence for short-distance (10s to 100s of meters) and long-distance lifetime dispersal distances (1 to 100s of km), a type of dilemma observed in many plants and animals called Reid’s Paradox. Attempts to resolve this paradox using population genetics strategies have been hindered in North America by the lack of gene flow-genetic drift equilibrium in most of this species' range related to its recent range expansion from the Great Plains across the Corn Belt to the Atlantic Coast. Analyses by Bermond et al. (2013) of transient genetic clines in Europe formed in the contact zone of invasion fronts of independently expanding populations yielded dispersal estimates of 13-21 km/generation. These indirect estimates based on gene flow indicate greater dispersal than direct observations of short-range movement, another kind of dilemma called Slatkin's paradox; however, the estimates are consistent with other types of behavioral evidence indicating adult rootworms can and do make long-distance flights. Based on the wide-array of available evidence, we present a conceptual model of adult western corn rootworm movement ecology. This model incorporates our conclusion that western corn rootworm populations consist of two behavioral phenotypes: residents, which disperse only locally by short-distance appetitive flights, and migrants, which engage in non-appetitive long-distance migratory flight in addition to short-distance flights. Together, the mixture of the different lifetime dispersal kernels of the two phenotypes resolve Reid's and Slatkin's paradoxes.
