256 Booth and Goettel: Control of Red Elm Bark Weevil by Trunk Injection of Azadirachtin was approximately 0.38 MPa at the start of the loading stroke and 0.45 MPa at the end of the stroke. Each injector delivered the en- tire contents into the tree within 10 to 15 seconds. Injection holes were then filled with silicone sealant. Injection was conducted between 8:00 a.m. and 12:00 noon on August 4 and 5, 2010. Con- ditions were as follows: August 4: at start 13°C, RH 89%, wind 4 km/h; at end 20o C, RH 53%, wind 4 km/h; Aug 5: at start 15o Sampling Insects Five yellow “Tanglefoot” (Contech Industries, Delta, British Co- lumbia, Canada) sticky traps 10 cm × 15 cm were established in each tree in the year following insecticide applications. A total of 120 traps were hung from branches 10 to 12 m above ground level at the beginning of each sampling period using a man lift, then removed and returned to the laboratory for count- ing the number of adult REBW. Collection and replacement of traps was conducted until populations generally declined. Sam- ples were taken one, two, three, and four weeks following de- tection of REBW. Traps were established in trees June 29–30, 2011, and sampling commenced between July 6 and 7, 2011. Statistical Analysis Data were analyzed using three reps for each treatment after cal- culating the means over the four subsamples. In addition, data were analyzed using only the two inner tree subsamples to de- termine possible effect of infiltration of emerging adults among treated and untreated trees, with the two outside trees acting as buffers. In both analyses, there were two treatments, four sam- pling times, and three reps available. The subsamples were gone after taking the means. A repeated measures analysis was used to account for possible correlations among sampling times. The data were analyzed using PROC MIXED (SAS Insti- tute, Inc. 2008), with “treatment,” “time,” and their interaction treated as fixed effects and “rep*treatment” as the random ef- fect. Since the same trees were sampled four times, “time” was treated as a repeated measure and various variance-covariance error structures were fitted and the one with the lowest AICC value was used in the final analysis. The analyses were done using the mean number of insects collected per card because the number of cards was not consistent across trees or sam- pling time due to periodic blowdown of traps. The UNIVARI- ATE procedure was used to check the residuals for normality and for potential outliers before performing the final analysis. RESULTS AND DISCUSSION There was a significant interaction between treatment and time when all four subsamples were considered (df = 1,12; F = 4.47; P = 0.025) as well as when only the two inner trees were con- sidered (df = 1,12; F = 3.27; P = 0.05). In the first week, 55% fewer weevils were trapped in the treated trees as compared to the untreated trees when all four subsamples were considered (Figure 1) and 60% when only the two inner trees were consid- ered (P < 0.05 in both cases). After the first week, mean num- ber of weevils trapped were similar among treated and untreated trees regardless if all four subsamples or only the inner trees ©2012 International Society of Arboriculture Figure 1. Mean trap count numbers of red elm bark weevils from treated and untreated American elm trees at Lethbridge, Alberta. Twelve trees were treated with TreeAzin Systemic Insecticide (5% azadirachtin) at a rate of 16 ml per 15 cm circumference using the Ecoject Microinjection System. Twelve trees acted as controls. Groups of four contiguous trees per replicate were alternated, creating three treatment groups and three control groups. Aster- isk (*) denotes significant treatment effect (P < 0.05). CONCLUSION Late summer trunk injection with azadirachtin, using the Ecoject Microinjection System was shown to be effec- tive in reducing red elm bark weevil emergence the follow- ing year in American elms. However, the treatments did not prevent infiltration of weevils from adjacent non-treated trees suggesting that all potential host trees in an area would need to be treated for adequate management of this pest. Acknowledgments: Resources and personnel were provided by the Le- thbridge Research Centre. We would like to thank Dr. R. Byers and Mr. D. Mullin for their assistance, and Mr. T. Entz for statistical analysis. LITERATURE CITED Booth, M., and D. Johnson. 2009. Pressurized-canister trunk injection of acephate, and changes in abundance of red elm bark weevil (Magda- lis armicollis) on American elm (Ulmus americana). Arboriculture & Urban Forestry 35(1):14–51. Doccola, J., P.M. Wild, I. Ramasamay, P. Castillo, and C. Taylor. 2003. Efficacy of arborjet viper microinjections in the management of hem- lock wooly adelgid. Journal of Arboriculture 29: 327–330. Doughty, S.C., D.K. Pollet, R.J. Constantin, D.W. Wells, and K.L. Koonce. 1992. Paint-on application of acephate for aphid control on crape myrtle. Journal of Arboriculture 18:94–97. C, RH 86%, wind 4 km/h; at end 22°C, RH 54%, wind 13 km/h. were considered. Researchers presume that at this time most of the beetles would have emerged from the trees and the beetles being trapped were dispersing among the trees. Beetle num- bers dropped after the third week so sampling was terminated. The insect’s emergence commences in early spring with males followed by females approximately one week later. Because the females aren’t gravid when they emerge, they require time to feed, mate, and commence laying eggs (Booth unpublished ob- servations 2010). By recognizing this, the study authors suggest that injections be applied in late summer or autumn to allow for delayed egg hatching ensuring that all larval stages are targeted.
November 2012
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