Evidence for regional variation in the thermal biology of Dendroctonus rufipennis (Kirby) (Coleoptera: Curculionidae, Scolytinae) in Colorado
Date
2018
Authors
Dell, Isaac Hans, author
Davis, Seth, advisor
Kondratieff, Boris, committee member
Redmond, Miranda, committee member
Stephens, Sky, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Dendroctonus rufipennis (Kirby) (Coleoptera: Curculionidae, Scolytinae), the spruce beetle, is native to the forests of western North America where it is the primary cause of Engelmann spruce Picea engelmannii Parry ex Engelm. mortality. This study is an effort to further the knowledge of ecological conditions that affect D. rufipennis flight phenology, abundance, and fitness traits. Spruce beetle populations were monitored for two years at high elevation spruce forest sites; during this period of time 32,881 spruce beetles were captured, as well as significant quantities of off-target species. Trapping sites were classified by variation in thermal trends using hierarchical cluster analysis which revealed statistical support for two groups of sites (cold' and 'warm'). A logistic function was used to model cumulative proportion of trap capture by day-of-year for all sites; and modeled phenologies indicated that beetles from cold sites terminate their flight period significantly earlier than beetles from warm sites. Additionally, the flight season is prolonged at warm sites, suggesting that hosts at warmer sites are exposed to beetle pressure for longer periods of time. At higher latitudes, the flight period was significantly longer than at lower latitudes, but there was no relationship between spruce beetle flight phenology and elevation. There was a significant female bias in the sex ratio at cold sites, but sex ratios were even at warm sites. Fitness traits (body size) varied along both latitudinal and elevational gradients; a negative correlation between elevation and pronotal width was observed indicating that beetles were smaller at high elevations, but beetles tended to be larger at high latitudes. Correlations between spruce beetle abundances in traps and the abundances of predators and competitors were evaluated, but there was no evidence that either feeding guild was negatively impacting spruce beetle abundances. The results of this study suggest that fine scale environmental variation must be considered when managing or monitoring spruce beetle populations, as both site-level thermal variability and latitude are associated with variation in the flight period and corresponding biotic pressure on host trees.