Modelling and Mapping Geographic Ranges to Evaluate Weed Biocontrol Agents: A Case Study Using Altica carduorum (Coleoptera: Chrysomelidae) and Cirsium arvense (Asteraceae)
Leaf - feeding beetles , Altica carduorum, from a population in NW China have been identified as candidate agents for biocontrol of Canada thistle , Cirsium arvense. This paper assesses the potential of beetles from this population to establish on the Canadian prairies . A phenological model is applied to determine where sufficient heat accumulates to allow completion of at least one generation per year . The model was applied both with and without a submodel of adult thermoregulation . The model was driven using meteorological data from a grid covering the agricultural region of the Canadian prairies , i . e . ca . 670 000 km 2 , at a resolution of (50 50) km . In each grid square , the percentage of the years 1960 - 89 for which the model indicated that at least one generation could have been completed was calculated; these proportions were categorized (0 - 80%; 80 - 99% and 100%) and mapped . Maps of C. arvense density over the simulation region were also produced , and compared to the maps of predicted beetle distribution . The model suggests that A. carduorum could establish over much of the prairies . Without thermoregulation , the predicted range (i . e . the area in which one generation was completed in every year) is restricted to the warmer parts of the prairies , where C. arvense is generally sparse . Inclusion of thermoregulation almost doubled the predicted range to cover most of the range of C. arvense on the Canadian prairies , missing only the cooler peripheral areas . These results suggest that this strain of A. carduorum has potential to overlap the range of C. arvense on the Canadian prairies , and so has potential to control this weed .