Koch (2008) modelled the spatial-temporal extent of the Redbay Ambrosia Beetle (Xyleborus glabratus, RAB) in the Eastern U.S. using a GIS based approach. This study involved using a cost-weighted distance analysis based on historical data for distribution, climate, and host species density. The RAB attacks host Redbay and Sassafras trees and injects them with a fungal symbiont (Raffaelea lauricola), causing host death due to vascular disease (Koch 2008). The RAB and MPB are both in the same subfamily of weevils, Scolytinae, and share similar life history traits and strategies (e.g. fungal symbiosis). Due to the similiarties in ecology between the RAB and the MPB, this study mimics the methodology as outlined in Koch (2008) in attempt to create a similar analysis and end product maps for the MPB (Fig. 2).
Fig. 2: Cost-weighted distance analysis contours for the predicted RAB spread (Koch 2008)
Koch (2008) bases their analysis around 4 components needed to understand the future spread of the RAB:
- The current distribution
- The rate of spread
- Host-density
- Climate Suitability
To account for the uncertainty around specific ecological parameters they made a few key assumptions:
- The rate of spread will remain similar to the average rate of historical spread
- That the ability for the RAB to establish in an area is related to the density of host trees, Redbay and Sassafras
- That the RAB will be limited by the same climatic conditions characterized by their historic extent
For this study, the current distribution of the MPB, the spread of the MPB in the past, the current density of pine trees, and limiting climate conditions have to be understood. For the rate of spread and density of pine trees, the information can be derived through spatial analysis. As well, it is known that MPB mortality rates reach 100% at -40oC and has been a historic limiting factor in the northern range of the MPB (Safranyik et al. 2012). From this, the protocol outlined in Koch (2008) can be followed for performing a cost-weighted distance analysis.
