120 Pines and Westwood: Mark-recapture Technique for Native Elm Bark Beetle Table 2. Trap log surface area, number of exit holes, and brood galleries by year for spring and summer marking experiments 1994 to 1996. Year 1994 1995 1996 No. of trap logs 28 24 11z zTotal of 68 logs used, 11 dissected. consistent with Swedenborg et al. (1988) who described a 6-week period of spring emergence for H. rufipes. Because the actual emergence dates of individual beetles could not be deter- mined, it is impossible to predict how long marked beetles had been active at the date of capture. There was little evidence of marking powder on trees in the spring experiments by the end of May; thus, based on the July captures, it is conceivable that marked beetles lived 1 month or more after emergence in the spring. The summer trap logs were protected from weathering for several months. It is difficult to determine how long marked beetles were active in fall. Future research should examine a narrower window of emergence to determine actual lengths of flight periods for beetles. There was a low recapture rate, especially when examining the Summer 1994 and 1995 marked beetle captures in comparison to the exit hole counts. Low marked beetle capture rates may have been the result of low marking effectiveness of the powder or we simply did not capture a greater portion of marked beetles. In 1994 and 1995, marked adults were captured at all trapping distances in both spring and summer experiments. Many marked beetles were caught near the marking sites after emerging from tree bases or summer brood material. Similarly, Swedenborg et al. (1988) found that beetles land on nearby trees after emer- gence before flying again. Kaston (1939) also suggested that emerging beetles will not attempt to fly long distances if satis- factory elm material is nearby. Our study found no significant difference in the percentage of marked beetles caught 20 m (66 ft) or less from the center of the marking sites in the spring and summer experiments. In Summer/Fall 1996, Tanglefoot bands captured greater numbers of beetles in comparison to the Scout and Delta sticky traps used in previous experiments. The majority of beetles caught in the Summer 1994 and 1995 experiments were captured in August after which adult captures declined. Sweden- borg et al. (1988) also reported that sticky trap captures dimin- ished in September. The dense beetle numbers on the top portion of Tanglefoot bands used in 1996 suggests bark beetles may be walking down the bole of the tree to construct overwintering sites at the base of elm trees. Anderson (1996) found that after a frost event in which temperatures fell between –6°C (42.8°F) to –10°C (50°F) in late October, there immediately followed a ma- jor increase in overwintering activity by native elm bark beetles. The Scout and Delta sticky traps may be more efficient in capturing adults during the spring and early summer months when the beetles are actively flying rather than in the fall when temperatures are cooler. The complete encirclement of the tree by the Tanglefoot band may also facilitate a higher capture rate of crawling beetles than the Scout and Delta sticky traps used. There were many live elm trees remaining in the forest stands at the conclusion of each experiment and most marked beetles ©2008 International Society of Arboriculture were caught within 20 m (66 ft) from release trees. Beetles may have remained in the sites to feed or overwinter on the remaining live elm trees. Anderbrant and Schlyter (1987) found European Dutch elm disease vectors seldom dispersed more than 50 m (165 ft) from infested elm stands over a period of several years, but did not report on beetle movement once host trees became scarce and did not mark beetles. Research using mark and re- capture techniques is needed to determine if the dispersal behav- ior of the adult beetles changes as the percentage of live elm trees declines in a stand. It is important to determine if marking techniques can be used to accurately track mass migrations of adults once hosts become scarce. Results from this study dem- onstrate that beetles can be easily marked and tracked. Experi- ments within buffer zones or forest edges surrounding towns and cities where Dutch disease management is practiced may be appropriate to determine if significance numbers of elm bark beetles are entering community urban forests (Westwood 1991). If a suite of management techniques (including survey, beetle control, and sanitation) is effectively carried out in buffer zones, the incidence of beetle movement into urban forests should be minimized. Future research should also investigate the effective- ness of Tanglefoot bands as an efficient monitoring tool to further elucidate the movement of beetles on tree trunks. Acknowledgments. We thank T. Paton and N. Normandeau for tech- nical assistance and two anonymous reviewers for improving the manu- script. Funding was provided by Manitoba Conservation, Forestry Branch, Government of Manitoba, and the Centre for Forest Interdisci- plinary Research, University of Winnipeg. LITERATURE CITED Anderbrant, O., and F. Schlyter. 1987. Ecology of the Dutch elm disease vectors Scolytus laevis and S. scolytus (Coleoptera: Scolytidae) in southern Sweden. Journal of Applied Ecology 24:539–550. Anderson, P.L. 1996. Overwintering behaviour of the native elm bark beetle, Hylurgopinus rufipes (Eichhoff) (Coleoptera: Scolytidae), in Manitoba. MSc Thesis, University of Manitoba. pp. 1–109. Anderson, P.L., and N.J. Holliday. 2003. Distribution and survival of overwintering adults of the Dutch elm disease vector, Hylurgopinus rufipes (Coleoptera: Scolytidae), in American elm trees in Manitoba. Agricultural and Forest Entomology 5:137–144. Birch, M.C., T.D. Paine, and J.C. Miller. 1981. Effectiveness of phero- mone mass-trapping of the smaller European elm bark beetle. Cali- fornia Agriculture 35:6–7. Brazier, C.M. 1991. Ophiostoma novo-ulmi sp. nov. causative agent of the current Dutch elm disease pandemics. Mycopathologia 115: 151–161. Cook, S.P., and F.P. Hain. 1992. The influence of self-marking with fluorescent powders on adult bark beetles (Coleoptera: Scolytidae). Journal of Entomological Science 27:269–279. Mean ± SEM trap log surface area (cm2) 1501.1 ± 79.4 1409.4 ± 85.2 1614.6 ± 149.6 Total no. of exit holes 4195 4977 1383 Mean ± SEM no. of exit holes 149.8 ± 19.7 207.4 ± 31.3 125.7 ± 16.4 Mean ± SEM no. of brood galleries 32.7 ± 6.6 66.9 ± 12.4 129.6 ± 27.8
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