Arboriculture & Urban Forestry 43(6): November 2017 This “fly-off” assay rapidly distinguishes viable beetles (including ones initially feigning death), which invariably take flight from dead of mori- bund ones still remaining in the trays aſter 10 min- utes (Baumler and Potter 2007). The leaves were photocopied, the copies were scanned, and the amount of leaf area eaten was determined with the soſtware program Paint.NET v3.5.8 by adjusting the selection tolerance for each scan to determine the area of the whole leaf and the missing portions. The trial was repeated in 2012 using similar meth- odology, except the study site was an on-campus planting of mature (>8 m tall) Tilia cordata, resi- dues (including both carbaryl and bifenthrin as standards) were allowed to field-weather for 21, 14, or 7 days before being challenged with four JB per leaf and dish. Aſter 24 hours, beetles and leaves were evaluated for viability and feed- ing damage, respectively, as described above. Efficacy of chlorantraniliprole at reduced rates A trial conducted in July 2012 evaluated reduced rates of chlorantraniliprole (0.312, 0.156, 0.078, and 0.039 ml per L) for suppressing JB defolia- tion of Tilia cordata compared to the label rate of carbaryl (Table 1) and untreated check. Meth- odology was as above except that only one spray timing (seven days before challenge) was used. Control of evergreen bagworm on arborvitae Several hundred mid-sized bagworms were col- lected from an untreated arborvitae (Thuja sp.) hedge in Lexington, Kentucky, on 18 June 2012, and held without food for 24 hours. Test cham- bers were made from covered clear plastic cups (473 ml) with a florist’s water pick inserted through the lid over which a second clear plastic cup was inverted to form a cage. Twigs of arbor- vitae (7.5 to 9.0 cm long) were sprayed on both sides with either chlorantraniliprole (0.312 ml/L), Bacillus thuringiensis var. Kurstaki (Thurcide; Certis, Columbia, Maryland, U.S.) at 15.6 ml/L, or left untreated as checks. Residues were allowed to dry, then a single twig was inserted into each water pick, and a single bagworm was placed on the twig. There were 40 arenas (replicates) per treatment. Bagworms were assessed for survival after 48 hours. Frass pellets produced by the 245 bagworm during the trial period were air-dried, counted, and weighed. The trial was repeated using late-instar bagworms collected from the same arborvitae hedge on 24 July 2012. Other procedures were the same as described above. At the latitude of Kentucky, evergreen bag- worms hatch in mid- to late May and develop through seven larval instars during their 10–13 week feeding period. Instar distributions used in the trials were assessed by measuring head cap- sule widths (Kaufmann 1968) of 20 larvae at the conclusion of each assay. Larvae in the first trial were fourth and fiſth instars (10% and 90%, respectively), and in the second trial were sixth and seventh instars (32% and 78%, respectively). Control of eastern tent caterpillar on crabapple Two trials were conducted targeting early-mid or mid-late instar eastern tent caterpillar (ETC) with 1- or 14-day-old residues of chlorantra- niliprole (0.312 ml/L), respectively. Spinosad was included as a standard, along with untreated checks. Intact twigs with leaves on a mature choke- cherry tree (Prunus virginiana) on the University of Kentucky campus were blocked by size and within-canopy location, tagged, and sprayed to runoff on 18 April 2016. Residues were allowed to field-dry for 24 hours; then five replicates of treated twigs with five or more intact leaves each were harvested, trimmed to 15–20 cm length, and inserted into florists’ water picks in arenas similar to those described for the bagworm trials. Tents containing ETC larvae were harvested from wild black cherry trees (Prunus serotina) in Madison Co., Kentucky, on 19 April 2016. Ten ETC (mix of second and third instars) were intro- duced to each arena and allowed to feed for 24 hours. Larvae were then scored as dead, mori- bund (slight twitching only in response to probe), or alive (crawling, defensive twitching, or capa- ble of flipping over within three seconds). Each cohort was then rated for number of fecal pellets produced during the assay (1–5 scale correspond- ing to <10, 10–20, 21–50, 51–100, or >100 pellets, respectively) and amount of overall feeding on the leaves was assessed as described for the JB assays. The trial was repeated by harvesting twigs with foliage with 14-day-old residues from the same ©2017 International Society of Arboriculture
November 2017
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