Effects of attraction radius and flight paths on catch of scolytid beetlesdispersing outward through rings of pheromone traps

Results were analyzed from six previous studies in which marked bark and am brosia beetles, Ips typographus, I. paraconfusus, and Trypodendron lineatum (Coleoptera: Scolytidae), were released at the center of concentric rings of pheromone traps. Assuming nearly straight flight paths, a "filtering" eq uation model predicts recapture percentages on several trap rings of specif ied radii, trap numbers, and effective attraction radius (EAR) of a pheromo ne trap. Equations were used to calculate recapture percentages on concentr ic trap rings as a function of increasing EAR and gave polynomial relations hips for each ring with terms equal to the number of inner rings plus one. Results were confirmed by computer simulations. Filtering equations were it erated with increasing EAR values to find one that gave a recapture percent age for the innermost trap ring that matched the field results. The estimat ed EAR for a synthetic pheromone bait of I. typographus was similar in five tests (range 1.39-1.78 m), but in two other tests was larger (3.27 and 15. 9 m). The EAR for pheromone of 75 male I. paraconfusus in ponderosa pine lo gs ranged from 0.35 to 34.5 m (mean of 4.7 m) and was generally larger for previously pheromone-responding beetles than for freshly emerged ones. For T. lineatum, the EAR of lineatin-baited traps at 100-m radius was 2.43 m. R ecaptures of I. typographus were reasonably predicted by the estimated EARs in the filtering model. To obtain perfect fits, another model assumed the EAR could Vary with ring radius (dispersal distance) and found that the EAR for I. typographus decreased with dispersal distance in four experiments, but increased or was variable in two others. However, in I. paraconfusus an d T. lineatum, the EAR increased with dispersal distance. Simulations that varied combinations of the EAR and random angles of maximum turning (AMT) o f beetles stepwise showed that a nearly straight flight path for I. typogra phus explained observed catches on trap rings best, while a higher AMT of 3 6 degrees was better to explain catches of T. lineatum. Simulations show th at catch per trap ring in relation to radial distance can be influenced by the beetle's AMT (still unobserved in the field). A conceptual model of dis persal and host selection in "aggressive" bark beetles with regard to pione er and joiner colonization strategies is presented.