The Columbian Timber Beetle, Corthylus Columbianus. VII. The Effect of Climatic Integrants on Historic Density Fluctuations

Multiple regression analyses were used to relate population fluctuations of Corthylus columbianus Hopkins in basal sections of red and silver maple ( Acer rubrum L., A. saccharinum L.) with summer and winter temperature, precipitation, and number of days flooded. Based on a sampling of 3500 beetle attacks in southern Indiana, precipitation accounted for most of the variation (61 percent), followed by flooding (19 percent) and temperature (12 percent). The best model, incorporating all three variables, accounted for 95 percent of the variation in beetle density through time. The addition of a variable for tree growth did not add strength to the model. Investigations into other geographic areas of Indiana demonstrated a similar relationship. The analyses emphasize the additive effect of previous climatic conditions on beetle population changes and give added emphasis to the climatic release hypothesis.