Dispersal and re-capture of marked, overwintering Tomicus piniperda (Coleoptera : Scolytidae) from Scotch pine bolts

The pine shoot beetle (PSB), Tomicus piniperda is a recently established ex otic pest of live pine in the southern Great Lakes region of the U.S. and C anada. Scotch pine, Pinus sylvestris L. is the most susceptible pine specie s, but the adult also attacks several other North American species of Pinus . This research investigated the dispersal behavior of beetles emerging fro m overwintering sites to aid in the development of effective monitoring and management practices. Scotch pine logs with overwintering PSB were sprayed with fluorescent pigments to mark dispersing beetles. These logs were plac ed in piles in the centers of three circular trap arrays of 8-unit Lindgren traps, baited with a-pinene, and placed at distances of 50, 100, 200, 300 and 400 meters from the center along equally spaced radii. An estimated ave rage of 393 PSB, or 23.4% of the overwintering PSB, dispersed from each of three log piles during the initial spring dispersal flight, and 21.9% of th ese were captured in traps. Traps within 100 meters caught 56.0 to 67.8% of the marked PSB recovered. Most (95.3%) marked PSB were trapped within 400 meters, but 12 beetles (4.7%) were trapped 780-2,000 meters away in adjacen t trap arrays. The dispersal pattern of the population, as indicated by tra p catch, was to the northeast, in the direction of prevailing westerly/ sou therly winds up to 4.77 m/s daily average during beetle flight. Regression analysis suggests that the PSB within the experimental area had a predicted dispersal distance of 900 meters in an area that contained numerous traps. Dispersal distances may be greater under of conditions of strong and stead y winds or if traps or abundant host material removed fewer PSB from the di spersing population. The use of traps to monitor specific sites should cons ider the direction of prevailing winds. Trap catches of wild PSB suggest th at optimal inter-trap spacing for efficient detection could be about 78 m.