The western corn rootworm, Diabrotica virgifera virgifera Leconte (Coleoptera: Chrysomelidae), was accidentally introduced near Belgrade in Serbia just before 1992 and from there its expansion into Europe started. We have estimated its mean rate of expansion from 1992 to 2000 to be approximately 33 km year − 1 , using data from the annual surveys of the European and Mediterranean Plant Protection Organisation.We investigated whether or not D. virgifera can establish itself at certain places in Europe, taking its temperature-dependent development into account. We also estimated the time it will take D. virgifera to reach the Netherlands, considering only its dispersal by flight. All life stage transitions of D. virgifera were simulated with the program INSIM to assess whether or not it could establish itself in particular places. In the simulations, we used the available laboratory data on its life history characteristics, as well as a time series (2 -6 years) of daily minimum and maximum temperatures from weather stations across Europe. The temperature-dependent net reproduction resulting from the simulations showed that D. virgifera populations cannot establish themselves at latitudes above 55 ° N.The overall expected velocity of D. virgifera 's range expansion was computed with van den Bosch et al.'s formula [van den Bosch F, Hengeveld R & Metz JAJ (1992) Analysing the velocity of animal range expansion. Journal of Biogeography 19: 135 -150], where the expansion velocity was based on dispersal characteristics and demographic parameters. We predicted that D. virgifera will not reach the Netherlands by flight from the border of its 2000 range before 2018 using this overall expected velocity. The explanation of this late arrival is that the velocity of population expansion decreases in all directions from the centre of its 2000 range due to unfavourable temperatures.Our analysis is an improvement on former analyses in that it uses temperature-dependent life history characteristics. We stress, however, that the lack of knowledge on dispersal behaviour and on the values of life history characteristics in field situations might severely limit the applicability of the predicted velocity.
In teaching epidemiology, confounding is a difficult topic. The authors designed active learning objects (LO) based on manipulable three-dimensional (3D) plots to facilitate understanding of confounding. The 3D LOs help illustrate of how confounding can occur, how it generates bias and how to adjust for it. For the development of the LOs, guidelines were formulated based on epidemiology and theories of instructional design. These included integrating the conceptual and empirical aspects: the causal relationships believed to be operating in the study population (conceptual aspect) and data-oriented associations (empirical aspect). Other guidelines based on theories of instructional design included: actively engage the students, use visual methods when possible, and motivate the students about the importance of the topic. Students gave the method strong positive evaluations. Experts in epidemiology agreed that the 3D LOs apply generally accepted scientific views on confounding. Based on their experiences, the authors think that the 3D plots can be useful addition in the teaching of confounding. The article includes links and a downloadable file that provide a demonstration of the 3D LO-based teaching materials.
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