Using matrix population models to inform biological control management of the wheat stem sawfly, Cephus cinctus

In this study, we constructed a matrix population model to assess the potential effectiveness of biological controls against the wheat stem sawfly, Cephus cinctus, a major pest of wheat in North America. We calculated the sensitivity of C. cinctus population growth to changes in stage-specific survivorship, to identify the stage at which parasitoid attack would have the largest impact on pest population growth. We also calculated the stage-specific rate of mortality needed to reduce C. cinctus population growth rate to zero, to set targets for conservation biological control approaches. Our model indicates that C. cinctus populations are growing (λ = 1.022), and are predicted to triple in a year in the absence of added control measures. The winter larval stage had the highest elasticities, suggesting this stage is the weakest link in the pest life-cycle, in part reflecting the much longer average duration of the winter compared with the summer larval stage (45 versus 5 weeks). Parasitism levels by native Bracon spp. parasitoids necessary to suppress C. cinctus population growth were the same for summer and overwintering stages (68%). These target parasitism levels far exceeded those typically observed in the field, and conservation measures employed to date suggest that single actions do not bolster parasitism to target thresholds. Thus multiple conservation measures (e.g. reduced tillage, increased cutting height and the provisioning of floral resources) will likely need to...

Source: Biological Control - March 10, 2017 Category: Biology Source Type: research