Participants in the OGIA/OSU Greater Cincinnati BYGL! Diagnostic Walkabout held this past Monday at the Boone County Arboretum observed the unusual damage caused by the Redbud Leaffolder (Fascista cercerisella, family Gelechiidae) on its namesake host (Cercis canadensis). Populations of this native moth appear to be sporadic and highly localized in Ohio this season. However, where populations are high, damage can be very noticeable.
The caterpillars use silk to stitch together leaf edges to produce nests that conform to the "leaffolder" common name that's approved by the Entomological Society of America (ESA). Pulling apart the fold will expose the silk stitching.
However, some nonconformist caterpillars make nests like a "leaftier" by stitching together neighboring leaves. In fact, I typically find a far greater number of leaves that have been tied together rather than folded. My observation is apparently shared by others with various online resources referring to the caterpillars as the “redbud leaftier” although this commonly used common name is not approved by the ESA.
Caterpillars live between the leaf layers where they feed beneath strands of heavy silk. Late instars commonly live in silk tubes festooned with frass pellets. They emerge out of their protective tubes to feed.
The caterpillars feed as skeletonizers, consuming the upper and lower leaf surfaces. The affected areas turn light brown then dark browh which sharply contrasts with the normal dark green color of the foliage.
Early instar caterpillars are cream-colored and have no discernible markings. As the caterpillars mature, markings begin to develop with alternating segments darkening to produce a striking appearance of black and light-green bands running the length of the body. Late instar caterpillars resemble a tiny, banded sea krait snake.
When disturbed, caterpillars in all instar stages will wiggle back and forth violently further enhancing their tiny snake impersonation. They have great entertainment value!
There has been little research attention given to the developmental biology of the leaffolder. Various online references report that there are two to three generations per year. I believe there are at least two and perhaps three generations each season in Ohio. However, it’s common to find both early and late instar caterpillars in the same nest as the season progresses making it difficult to separate the generations.
Like fall webworms (Hyphantria cunea), the velvety black female leaffolder moths tend to lay their eggs on or near the leaves from which they developed. So, the leaffolding / tying nests expand with each new crop of caterpillars.
Consequently, the most significant damage occurs late in the season. The moth spends the winter as pupae in debris and fallen leaves beneath infested trees.
Redbud leaffolder nests are common on wild eastern redbuds. However, infestations on established trees are mainly an oddity and tend to be light and irregularly distributed throughout the canopy. The caterpillars seldom represent a threat to the overall health of the trees. On the other hand, heavy damage to wild redbud seedlings may potentially cause significant injury.
Potentially damaging populations may also occur on weeping redbuds. It’s an open question whether high populations on weeping redbuds are related to a host preference based on food value, or if it’s a physical preference. The vertical orientation of the leaves causes them to naturally overlap which may make it easier for the caterpillars to tie multiple leaves together. Of course, the cascading leaves certainly make the leaffolder damage more obvious.
I could only find one study that mentions possible host preferences among redbuds. The study was conducted in the U.S. National Arboretum and published in 2007. The authors observed that Chinese redbuds (C. chinensis) with semi-rugose leaves were resistant to the redbud leaffolder. However, no host evaluation data was presented, and no observations were reported on native redbuds.
Although redbud leaffolder damage to landscape trees seldom affects the tree’s overall health, it can seriously reduce the tree’s aesthetic appeal, particularly on weeping redbuds. Where practical, populations can be reduced by pinching nests to kill caterpillars. Raking and destroying fallen leaves will reduce but not eliminate localized numbers by taking the overwintering pupae that remain attached to fallen leaves out of the picture. However, some pupae may be left behind in the duff.
Be Alert to Interlopers
Several years ago, I received a redbud leaf sample in a plastic bag from a homeowner. The leaf had clearly been a former abode of redbud leaffolder caterpillars. However, an earwig (order Dermaptera) was also included in the bag. Their conclusion was that the folded leaf damage was the work of the earwig. Of course, the earwig was either an innocent bystander simply hiding during the day in the folded leaf, or it may have eaten the caterpillars and taken up residence in their cozy quarters. Although earwigs are generally considered to be scavengers, they won’t refuse a little live meat.
Last year, I reported finding a rare cricket in a folded leaf [see “A Most Unusual Cricket,” https://bygl.osu.edu/node/2026 ]. The find was made interesting owing to the name commonly applied to the cricket: Carolina Leaf-Roller Cricket (Camptonotus carolinensis). The cricket belongs to the family Gryllacrididae, the Raspy Crickets.
The Carolina leaf-roller produces silk from modified labial salivary glands, an ability shared with several other family members. Also, this cricket can’t jump, an inability shared with all family members.
However, I didn’t believe the Carolina leaf-roller that I found was living up to its name. The folded leaf had frass-filled silk along with distinct silk stitching. Both are characteristic of redbud leaffolder caterpillars. Also, the redbud had numerous leaves folded or tied together by leaffolder caterpillars. I believed the cricket had taken advantage of a pre-fab home.
On the other hand, raspy crickets are described as opportunistic feeders eating whatever comes their way from meat to veggies. There was a possibility the cricket had found a bed and breakfast and enjoyed a caterpillar-meat meal before settling into its new digs.
Spiders are also commonly found in abandoned redbud leaffolder nests. Indeed, we observed one nest on a Secrest Arboretum redbud that contained a small spider guarding a clutch of spiderlings.
Redbud Leaffolder Management in Nurseries
Although the redbud folder isn’t considered a tree health-threatening pest in forests or landscapes, heavy leaffolder activity on nursery stock can affect marketability. Eric Rebek (Oklahoma State University (the other OSU), Dept. of Entomology and Plant Pathology) published two insecticide efficacy trials in 2011. The first trial focused on systemic insecticides. The second involved foliar applications.
Soil applied Acelepryn 1.67SC (chlorantraniliprole) in the spring and fall at a rate of 7.4 ml./ft. of shrub ht. provided a 95.7% and 93.9% reduction in the number of live caterpillars, respectively. Merrit 75WP (imidacloprid) applied in the spring and fall at a rate of 1.9 gm./ft. of shrub ht. yielded 75.5% and 67.0% reductions, respectively. Surprisingly, Lepitect 97WSP (acephate) applied in the spring at a rate of 5.7 g/ft. of shrub ht. only reduced the number of caterpillars by 0.01%.
Even more surprising, the foliar-applied efficacy trial performed in late July revealed that Talstar P (bifenthrin) applied at a rate of 10.0 fl.oz./100 gal. was highly effective producing a 98.1% reduction in the number of caterpillars. The author did not speculate on how or why a non-systemic topically applied insecticide could be so effective against caterpillars presumably located out of the reach of such an application. The systemic neonicotinoid Acelepryn 1.67 SC applied at the rates of 1.0 fl.oz and 2.0 fl.oz./100 gal. provided a 71.2% and 75% reduction in the number of caterpillars.
Kidwell-Slak, D. and Pooler, M., 2007. Cercis breeding at the US National Arboretum: Improving Redbud Rootability and Combining Other Traits of Interest©. In Combined Proceedings International Plant Propagators’ Society (Vol. 57, p. 710).
Rebek, E.J., 2011. Evaluation of Foliar Applications of Acelepryn (Chlorantraniliprole) and DPX-HGW86 (Cyantraniliprole) for Redbud Leaffolder Control, 2009. Arthropod Management Tests, 36(1). p. G8
Rebek, E.J., 2011. Evaluation of Soil Applications of Acelepryn (Chlorantraniliprole) and DPX-HGW86 (Cyantraniliprole) for Redbud Leaffolder Control, 2010. Arthropod Management Tests, 36(1), p.G9.