118 Pines and Westwood: Mark-recapture Technique for Native Elm Bark Beetle Trap distances from the center release site increased for each summer marking experiment and the dbh recorded for trees with sticky traps and Tanglefoot bands (Table 1). In July 1996, polyethylene bands covered in Tanglefoot adhesive were used in an attempt to increase the number of beetles collected in the study (LaFrance and Westwood 2006). Traps and bands were changed on a monthly basis when possible and were removed at the end of October or early November. Trap logs were also removed from the field sites at this time and placed in cool storage until dissection could occur. Exit holes were counted and the number of adult brood galleries formed was determined for all logs used in 1994 and 1995. In 1996, 11 of the 68 logs were assessed as a result of time constraints. After Scout or Delta sticky traps and Tanglefoot bands were removed from trap trees in the spring and summer experi- ments, the number of marked and unmarked beetles per sample date was counted. Several sticky traps and Tanglefoot bands were selected and assessed for beetle distribution on the sticky surface. The relationship of tree size (dbh) and number of beetles captured per trap or band was examined to determine if tree diameter influenced capture rate. Analysis with Spearman rank order correlations showed no significant relationship between tree dbh and number of beetles caught per sticky trap or Tangle- foot band for all spring and summer release experiments. An unpaired t-test was used to compare the percentage of marked beetles caught near the center of the sites (within 20 m [66 ft] of marked trees) between the spring and summer experiments (Zar 1996). Analysis of variance was used to determine if there were differences in the number of beetle exit holes and brood galleries between years in trap logs. Before data analysis, the assumptions of normality and homogeneity for the variables of trap log sur- face area, number of exit holes, and number of brood galleries were tested by examining normal probability plots and inspect- ing graphs of residuals from a general linear model estimate against predicated values. Heterogeneity of residuals was found for all three variables and these were log-transformed to meet the requirements of a normal distribution (Zar 1996). All results are reported without transformation (actual values are shown in tables and figures) and an alpha value of P 0.05 was consid- ered significant for all statistical analyses. SPSS for Windows, release 11 (SPSS Inc., Chicago, IL) was used for statistical analyses. RESULTS AND DISCUSSION Native elm bark beetles were caught on traps starting 20 May, 29 May, and 23 May in 1994, 1995, and 1996, respectively (Figure 1). Peak flight activity occurred from 20 to 27 May, 6 June, and 7 June in 1994, 1995, and 1996, respectively. Marked beetles were captured on traps for each collection date in all 3 years except on 27 June 1995 (Figure 2). The length of time unmarked and marked beetles were collected was generally similar. Marked beetles were captured at the maximum distances from trap trees of 30 m (99 ft) in 1994, 50 m (165 ft) in 1995, and up to 750 m (2475 ft) in the spring of 1996 (Figure 3). For summer emergence experiments, native elm bark beetles were caught on traps or bands starting 27 July, 10 August, and 19 September in 1994, 1995, and 1996, respectively (Figure 4). The majority of beetles were captured in August in 1994 and 1995 and in October in 1996. Marked beetles were captured on traps for the majority of collection dates in all 3 years (Figure 5). Dates with no captures of marked beetles were 27 October 1994 ©2008 International Society of Arboriculture Figure 1. Capture of native elm bark beetles (± SEM) during spring emergence. and in 1995, 13 and 29 September and 1 November. After emerging from the powdered trap logs, marked beetles were captured at the maximum distances from the release sites each year: 20 m (66 ft) in 1994, 100 m (330 ft) in 1995, and 1000 m (3,300 ft) in 1996) (Figure 6). There was no significant differ- ence in the percentage of total marked beetles captured 20 m (66 ft) or less from the center of the release sites between the spring (1994, 1995, 1996) and summer (1994, 1995, 1996) experiments (spring 89.2%, summer 66.5%, t3 2.09, P 0.128). There were 4,195 and 4,977 beetle exit holes in all trap logs dissected in 1994 and 1995, respectively, whereas only a portion of the trap logs were dissected in 1996 . There was no significant difference in the mean trap log surface area of individual logs between years (F2,62 = 1.04, P 0.359, Table 2) and no dif- ference in the mean number of exit holes in trap logs between years (F2,62 = 0.22, P 0.797, Table 2). There were signifi- cantly more brood galleries formed in trap logs in the 1996 Figure 2. Percent of all native elm bark beetles marked and captured during spring emergence.
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