Arboriculture & Urban Forestry 41(2): March 2015 Small-Bolt Field Evaluation of Tree Protection Treatments Small bolts that were challenged by SPB in the field received lower beetle pressure (fewer attacks) than desired. In New Jersey, traps were baited to begin the exposure period on May 15, 2012, 62 days aſter trees were treated in central Louisiana. Treated bolts were deployed in a randomized complete block design at two sites. None of the four blocks at Clarks Landing received a sufficient number of control bolt attacks to indicate a valid test (Strom and Roton 2009), so they were excluded from analyses. At Clarks Landing, the mean number of control bolt attacks sitewide (across blocks) was 0.5 ± 0.29 (mean ± 1 SEM, n = 4). At the Harding site, bolts received more pressure from SPB, and the number of attacks on control bolts (6.5 ± 1.5, n = 2) exceeded the minimum attack threshold. This was also true in Mississippi (5.5 ± 1.5, n = 2). Bolts treated with either Astro or Onyx sustained no attacks and had no gallery construction at the Harding or Mississippi sites. In contrast, systemic imidacloprid treatments were considered ineffec- tive as they received >2 attacks per bolt on average. At the Harding, NJ site, Xytect bolts (mean = 9.5 ± 4.5, n = 2) and Dominion bolts (mean = 3.0 ± 1.0, n = 2) were both above the threshold for effectiveness, and the same was true for the Mis- sissippi site (Xytect mean = 20.5 ± 7.5; Dominion mean = 4.5 ± 2.5). Plans for additional replicates were abandoned due to the low number of attacks received on bolts in the field traps. Due to the low number of valid replicates achieved at the NJ and MS sites, researchers did not pursue the CI evaluation criterion or comparisons by ANOVA. Collections of insects from buckets in New Jer- sey revealed that the sex ratio of captured, intact SPB was strongly male biased, far more than expected. In the 10 replicates collected over the course of four days (50 buckets), total captures were: 233 female SPB; 4,334 male SPB; 5,153 cler- ids; 43 Temnochila virescens; and 42 D. terebrans. The number of female SPB is critical for bolt attack and therefore treatment challenge, and ranged from 0 to 91, with a mean of 4.7. The mean sex ratio (male:female) was 18.6:1 (94.6% male). The low number of female SPB and the high number of clerids are likely to blame for the lack of bolt attacks observed in New Jersey; more data 95 need to be gathered on lure effects on SPB sex ratio over a range of conditions so that female numbers can be more effectively manipulated. Field assessments using bolts from the treated trees were conducted in Louisiana with I. avulsus in three trials (Table 1; Figure 3). The first trial began on May 14, 2012 (58 days posttreatment), with bolts that were cut on May 11. There were two bolts per treatment. As expected, bolts received heavy attack pressures from I. avulsus with 100% of untreated control samples having beetle activity. Neither imidacloprid product was effective at reducing bolt use by I. avulsus: Xytect bolts had 25/30 (83.3%) samples positive and Dominion had 35/36 (97.2%). Onyx was also ineffective (17/33, 51.5%), leaving Astro (0/36) as the only treatment considered effective in this trial. The second trial began June 5, 2012 (83 days posttreat- ment), and resulted in a similar pattern. Control bolts showed a heavy challenge (38/39 samples positive, 97.4%), and Astro was the only effec- tive treatment (0/30 samples positive). Dominion (30/33, 90.9%), Xytect (37/42, 88.1%), and Onyx (27/42, 64.3%) were ineffective. The third and final evaluation with I. avulsus began on July 18 (126 days posttreatment). In this trial, control bolts showed a valid test (36/36 samples positive) and none of the treatments were effective. In addition, their relative effectiveness ranking had changed: Dominion were the poorest performer (30/33, 90.9%), followed by Onyx (24/36, 66.7%), Astro (19/33, 57.6%), and Xytect (14/27, 51.9%). Small-Bolt Laboratory Evaluation of Tree Protection Treatments In the three laboratory trials, treatments received a more vigorous challenge from SPB than in the field trials (Figure 4). Two experimental trials were conducted with NJ beetles and one with MS beetles (Table 1). Each laboratory trial resulted in a valid test, with control bolts averaging 28.6 + 1.5 attacks across the three trials. As in the field portion of the study, only the bole sprays, Onyx and Astro, effectively reduced or eliminated SPB attacks. In two trials, attacks and gallery lengths were zero, while in the third, each of these two treatments had a single bolt that received one attack. The imidacloprid systemic products were ineffective by either of the criteria, each averag- ©2015 International Society of Arboriculture
March 2015
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