The invasion of Europe by the western corn rootworm, North America's most destructive corn pest, is ongoing and represents a serious threat to European agriculture. Because this pest was initially introduced in Central Europe, it was believed that subsequent outbreaks in Western Europe originated from this area. Using model-based Bayesian analyses of the genetic variability of the western corn rootworm, we demonstrate that this belief is false: There have been at least three independent introductions from North America during the past two decades. This result raises questions about changing circumstances that have enabled a sudden burst of transatlantic introductions.

SUMMARYTwo techniques for collection of water-soluble substances, particularly carbohydrates, from the leaf surfaces (phylloplane) of maize {Zea mays L.) were compared in order to explain the oviposition preference ofthe European corn borer.By dipping the leaves in water, smaller amounts of substances were obtained than by spraying water. The total amounts of three sugars (glucose, fructose and sucrose) collected from maize phylloplane ranged from 0-6 to 3-6 mg m"^ of leaf surface.The quantities of these substances varied with the variety of maize, with leaf position, and with the part of the leaf. Sugar ratios on the phylloplane were quite different from those observed within the leaf.