A CLIMEX model for Diabrotica virgiferavirgifera (western corn rootworm), was initially fitted to the known range of this pest in the USA and Mexico under rain-fed agricultural situations. When this model was projected into Europe, it became clear that soil moisture thresholds for irrigation differed markedly between Central Europe and the USA. A second model was fitted using soil moisture parameters derived from theoretical expectations, and was found to fit the known distribution of all North American locations well, and all the European distribution records perfectly. Globally, the modelled potential range of D. v. virgifera covers approximately 64% of the global area of maize production. The highest nascent biosecurity risks to maize-producing areas posed by the western corn rootworm are China, Japan, Argentina, South Africa and Australia. Biosecurity agencies concerned with managing D. v. virgifera invasion risks to Asia should adopt a regional approach to the problem, attempting to slow its spread through Eurasia. The sensitivity of D. v. virgifera’s modelled potential distribution to the inclusion of irrigated sites in the model training dataset highlighted the importance of carefully exploring the implications of land-use factors that might be practised in different ways in the model training area and the area of concern.