Chlorantraniliprole: Reduced-risk Insecticide for Controlling Insect Pests of Woody Ornamentals with Low Hazard to Bees

Control of Japanese beetles and feeding damage on linden

Three trials evaluated efficacy and longevity of chlorantraniliprole foliar sprays to control adult Japanese beetles (JB) and reduce their defoliation of linden (Tilia spp.), a preferred JB host plant. Beetles were field-collected with standard JB traps (Trécè, Adair, Oklahoma, U.S.), baited with food-type lures (2-phenyl-ethyl-propionate, eugenol, and geraniol, 3:7:3 ratio), and brought to the lab within four hours of capture. Sexes were separated by foretibial characters (Baumler and Potter 2007); males were discarded, and females were held overnight in bins with moist soil, without food, before each assay. Freshly caught beetles were used for each trial. All trials included an equal number of replicates with foliage from non-sprayed twigs as untreated checks.

Control of evergreen bagworm on arborvitae

Several hundred mid-sized bagworms were collected from an untreated arborvitae (Thuja sp.) hedge in Lexington, Kentucky, on 18 June 2012, and held without food for 24 hours. Test chambers 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 arborvitae (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 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 bagworms 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 capsule widths (Kaufmann 1968) of 20 larvae at the conclusion of each assay. Larvae in the first trial were fourth and fifth 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 chlorantraniliprole (0.312 ml/L), respectively. Spinosad was included as a standard, along with untreated checks. Intact twigs with leaves on a mature chokecherry 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 introduced to each arena and allowed to feed for 24 hours. Larvae were then scored as dead, moribund (slight twitching only in response to probe), or alive (crawling, defensive twitching, or capable of flipping over within three seconds). Each cohort was then rated for number of fecal pellets produced during the assay (1–5 scale corresponding 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 chokecherry tree on 2 May 2016, enclosing them in arenas as above, and challenging them with cohorts of five ETC (four fourth instar, one third instar) per arena. By then most of the ETC in central Kentucky had abandoned their tents for pupation, but researchers were able to collect enough tents with still-active larvae from black cherry trees in shaded locations to use in the assay. After the 24-hour feeding period, ETC mortality, fecal pellet production, and defoliation were evaluated as above.

Control of roseslug sawfly on rose

This trial was conducted on potted roses (Knockout® variety Radrazz PP#11836, about 61 cm tall) in 11.4 L pots, with six shrubs (replicates) per treatment. Treatments were chlorantraniliprole (0.312 ml/L), carbaryl (2.5ml/L), and untreated control. The insecticides were applied with a hand-held spray bottle on 01 May 2012, thoroughly wetting all adaxial and abaxial leaf surfaces of the whole shrub. Plants were held in the greenhouse for 24 hours to allow residues to dry, and then moved outdoors. There was no rain between treatment and the first (three days) challenge. Challenges were made at 3, 7, 14, and 21 days after application.

Late-instar bristly roseslug sawfly larvae were hand-collected from rose plantings in Lexington, Kentucky, immediately before each challenge and set up in the assays the same day. For each challenge, six sets of three undamaged connected leaflets were removed from plants. Leaflets were placed on moistened filter paper in a 9 cm Petri dish, and five roseslug larvae were placed on the surface of the leaflets. Test arenas were maintained at 26°C on a 14:10 light:dark cycle. Roseslugs were assessed for mortality after 24 hours, and then feeding damage (leaf area consumed) was measured as described for the JB trials.

Foliar sprays targeting lace bugs, aphids, and soft scale crawlers

A trial comparing efficacy of 1- or 7-day-old foliar spray residues of chlorantraniliprole and bifenthrin against hawthorn lace bugs was conducted on mature (>10 years old; 4–5 m tall) hawthorn trees (Crataegus viridis ‘Winter King’) on the University of Kentucky campus in 2016. On 03 August 2016, twigs with 5–10 leaves were tagged and sprayed to runoff at label rates (Table 1). There were six sets of twigs for each treatment and challenge date, blocked and distributed across six trees, with twigs within trees at least 1 m apart and non-sprayed twigs as checks. Another set of twigs was tagged and treated as above on 10 August 2016. On 11 August 2016, one leaf was removed from each twig; then the detached leaves with field-weathered residues (or checks) were placed into individual Petri dishes on moistened filter paper. There were six replicates per treatment and timing. Adult lace bugs were collected by beating branches of a heavily infested unsprayed hawthorn at a different campus location. Ten active adults were placed on the abaxial side of each leaf, leaves were then inverted, and the lidded plates were held at 25°C under a 14:10 light:dark cycle. After 24 hours, the insects were gently brushed off the leaves, leaves were removed, and the bugs were allowed three hours to crawl out of the open dishes and disclose their status as live and mobile. Bugs still in the dishes after three hours were probed, and those not capable of crawling or flipping over were scored as dead.

Another trial compared efficacy of chlorantraniliprole and bifenthrin sprays against oleander aphids (Aphis nerii) on small (10–15 cm tall) greenhouse-grown swamp milkweed (Asclepias incarnata var. ‘Ice Ballet’) plants in 10 cm × 10 cm pots. The plants were infested by placing field-collected swamp milkweed shoots with high numbers of aphids in the flats amongst the test plants and allowing the aphids to establish for four days before the trial. On 29 August 2016, 24 shoots, enough for eight replicates plus untreated checks, were selected and blocked by initial infestation level. Individual plants were gently sprayed to runoff using a hand-held spray bottle so that no aphids were physically knocked off the plants. Plants with aphids were then held in an incubator as described in the lace bug trial. Surviving aphids were counted after 48 hours.

Researchers also evaluated chlorantraniliprole as a foliar spray targeting active and newly settled oak lecanium scale nymphs that hatch from eggs laid by females on twigs and then move to leaves upon which they settle and feed from late spring through summer. The study site was a heavily-infested planting of mature willow oaks (Quercus phellos) in a parking lot on the University of Kentucky campus. The application was made on 09 June 2009 near the end of crawler hatch. Three twigs with ≥20 leaves each were tagged on each of four trees and the bark and foliage was sprayed to runoff with chlorantraniliprole (0.156 ml/L) or bifenthrin (0.78 ml/L), or left untreated. On 23 June 2016, 14 days after treatment, researchers harvested the tagged branches, brought them to the lab, and counted numbers of live settled crawlers on both abaxial and adaxial surfaces of five randomly chosen, fully expanded leaves per shoot, which were pooled to give a single total per shoot.

Systemic applications targeting boxwood pests

A trial assessing efficacy of autumn or spring soil drenches of chlorantraniliprole for systemic control of boxwood psyllid [Cacopsylla busi (L.)], and boxwood leafminer (Monarthropalpusi flavus (Schank)] was done on established boxwood shrubs (Buxus sempervirens) at the Lexington Cemetery, Lexington, Kentucky. Both pests have a single generation per year with key life history events occurring during leaf flush (hatching and feeding of psyllid nymphs; emergence and egg-laying by leafminer adults). Imidacloprid (Merit 75 WP) was included as a standard. The shrubs (0.6–0.9 m height) were located in four sections of the cemetery, were at least 100 m apart, with one shrub (replicate) per treatment in each section. The insecticides were mixed with water and applied as a basal drench using 2.33 L solution per meter of plant height at the rates listed in Table 1, without additional irrigation. Separate sets of shrubs were treated in October 2009 or April 2010. Total rainfall was 14.7 and 22.8 cm during the six week periods following the October and April applications, respectively, which was 3.8 and 7.4 cm above average for those periods.

Damage from boxwood psyllids was evaluated on 30 July 2010 by examining 20 twigs per shrub (10 each from the upper and lower canopy) and recording the number with characteristic rosettes of cupped, stunted, terminal leaves that result from the psyllids’ feeding during leaf flush.

Boxwood leafminers were sampled twice, on 04 May 2010 for larvae already in the leaves at the time of the October 2009 drench, and on 13 October 2010 for larvae originating from eggs laid in spring 2010. For the May sampling, researchers collected 10 mined leaves per plant from the 2009 flush of growth and counted the number with live larvae, pupae, or exit holes. For the October sampling, researchers removed 20 random twigs per shrub and stereoscopically examined the first five leaves on each twig for living larvae.

Another trial targeting boxwood leafminer was done on heavily-infested in-ground B. sempervirens (0.6–0.9 m height) planted at a wholesale nursery in Stamping Ground, Kentucky. There were five replicates, each in a separate nursery row, with skips (untreated plants) between treated ones in a given row. Rows were 2.44 m apart and separated by mowed grass. Insecticides were applied as a basal drench on 23 April or 13 May 2013, using 3.1 L solution per meter of plant height at the rates listed in Table 1, without additional irrigation. The two timings tested for possible differences in efficacy from application just before or soon after leaf flush, which is when adults emerge from the previous year’s leaves and oviposit in new leaves. Treatments included chlorantraniliprole (both treatment dates) and two standards: dinotefuran (23 April only) or thiamethoxam (13 May only), plus untreated checks. There was 19.1 cm total rainfall from 23 April to 1 June 2013, 4.8 cm above normal for that period, and during summer the plants received occasional irrigation from the nursery’s sprinkler system, as needed to maintain vigor. Efficacy was assessed on 09 October 2013 by clipping 10 twigs per shrub from all parts of the canopy. Three fully-expanded leaves from each twig were dissected, and the number of leaves (out of 30 per plant) with live miners and living larvae per leaf was recorded.

Systemic applications targeting rose pests

This trial evaluated autumn soil drenches of chlorantraniliprole for reducing foliar damage by roseslug sawfly larvae and JB in the following growing season. It was conducted on established, similar-sized (about 60 cm height) hybrid tea (‘Knockout’) rose shrubs growing in several mulched beds on the university campus. The layout was a completely randomized design with five replicates. Treatments included chlorantraniliprole and imidacloprid (Merit 2F) at the rates listed in Table 1, chlorantraniliprole at half rate (12.13 ml/m), and untreated checks. The insecticides were applied via basal drench (1 L per shrub) on 23 October 2015. The plants were not subsequently irrigated, but there was 11.9 cm of rainfall from 23 October to 1 December 2015, which was 1.3 cm above normal for that period.

Roseslug sawfly damage was evaluated 03 May 2016 by two observers who independently counted all current-year leaves on each shrub with that pest’s characteristic window-feeding and skeletonization. On 28 June, twigs bearing five intact leaflets each were harvested from each plant, placed in 0.24 L transparent dishes, and challenged with five field-collected JB females that had been starved overnight. The JB were allowed to feed for 24 hours, remaining leaf material was scanned to determine amount eaten (cm²), and beetle vigor was assessed with a fly-off assay. Methods were as described earlier for evaluating foliar sprays for JB on linden.