Published online by Cambridge University Press: 31 May 2012
Comparisons were made of frequency distributions of Ips avulsus (Eichh.) and Ips grandicollis (Eichh.) caught in window traps while these species were attacking fresh pine slash. Relationships between mean and variance of trap data indicated that the flight of I. avulsus was more highly aggregated than the flight of I. grandicollis. Three different indices of aggregation were calculated which quantitatively expressed the degree of flight aggregation in each species. Degree of aggregation during attack may be an index of aggressiveness since it determines beetle density which influences attack success on a living host. The relatively high degree of flight aggregation of I. avulsus may partly explain why this species is more frequently a killer of live trees than is I. grandicollis.