Spatial and temporal distributions of four bark beetle species (Coleoptera: Scolytidae) along two elevational transects in the Sierra Nevada.

摘要

Bark beetles (Scolytidae) are commonly recognized as the most important mortality agent in western coniferous forests. In this study, we describe the spatial and temporal distributions of the four major pine-infesting bark beetles at four sites along two elevational gradients on the Eldorado and Stanislaus National Forests. A total of 914,864 Dendroctonus brevicomis LeConte, 30,391 D. ponderosae Hopkins, 62,215 Ips paraconfusus Lanier, and 1828 I. pini (Say) were collected during the 3-year period. Total trap catch was negatively correlated with elevation for D. brevicomis and I. paraconfusus (P<0.003), but not D. ponderosae and I. pini (P>0.08). Approximately 84.3% of all D. brevicomis and 67.2% of all I. paraconfusus collected at Eldorado and Stanislaus were captured at the lowest elevation site (823 and 1000 m, respectively). Dendroctonus ponderosae was collected most frequently at the third highest elevation site at each transect (1829 and 1707 m, respectively). The distribution of D. ponderosae was aggregated among mid-elevation sites (1280-1829 m) as 68.8% of all captures occurred here. Ips pini was captured most frequently at the highest elevations, but in general relatively few individuals were collected during the course of this study. Dendroctonus brevicomis was active throughout the entire sampling interval at the lowest elevations, but at mid- and high elevations captures peaked in late spring followed by decreasing numbers of individuals collected throughout the year. At the lowest elevations, D. ponderosae exhibited a single peak in June at Stanislaus (Site E), and a bimodal distribution with peaks occurring in April and November at Eldorado (Site A). In general, D. ponderosae was active throughout the entire sampling interval at mid- and high elevations. The temporal distribution of I. paraconfusus was consistent among all elevations with peak activity occurring prior to July. Few consistent trends in flight periodicity were observed for I. pini. In general, elevation strongly affected the spatial and temporal distributions of these species..