Characterizing Flight Aggregation of the Southern Pine Beetle 12

Abstract

Spatial aggregation patterns of flying southern pine beetles, Dendroctonus frontalis Zimm., were studied using a systematic grid of sticky flight traps placed in 3 beetle infestations. Five methods of characterizing dispersion were compared: Lloyd's index of patchiness (IP), Morisita's index of dispersion (Iδ), the coefficient of dispersion (CD), the slope of Taylor's power function (b), and the slope (β) of Iwao's regression of mean crowding (m) on mean density (m*). All indices indicated a high degree of aggregation of flying southern pine beetles within the infestations. The indices varied, however, in their ranking of aggregation for the 3 study sites. IP and Iδ gave the same relative results while CD showed a different pattern. The two regression techniques showed no significant differences between slopes for the various study sites. The m*-m regression provided more information for interpretation and more potential for evaluating influences of system manipulations. It is recommended, therefore, for characterization of southern pine beetle aggregation within infestations. IP (which serves as the theoretical basis of the regression), is suggested for comparisons between daily aggregation patterns. The m*-m pairs to the 95% prediction limits about the regression line; pairs falling outside these limits represent aggregation patterns significantly different from the norm.