Participants in the OGIA/OSU Extension Diagnostic Walkabout held this past Monday in Cincinnati Parks’ T. M. Berry International Friendship Park observed the handiwork of our native Hydrangea Leaftier Moth (Olethreutes ferriferana, family Tortricidae) caterpillars. The moth’s caterpillars appear to feed exclusively on our native Smooth Hydrangea (a.k.a. Wild Hydrangea) (Hydrangea arborescens) as well as varieties and cultivars.
The Caterpillar (a.k.a. Wasp Meat Item)
The common name “leaftier” is based on the behavior of the moth caterpillars. Individual caterpillars apply sticky silk along the edges of newly expanding hydrangea leaves to cement or tie the leaves together. This creates a purse or envelope-like structure that surrounds newly developing leaves and flowers.
The leaf abodes may involve a single leaf or two leaves cemented together. The affected leaves fail to fully expand and become dark green, wrinkled, and gnarled. The oddball structures may superficially resemble plant galls.
The caterpillars develop inside the protective (mostly!) purse-like leaf structures, feeding on the leaves and flowers enveloped within the tied leaves. Opening the tied leaves reveals a single caterpillar housed within a silk-lined tube littered with dark green frass pellets. The small, green, semi-transparent caterpillars have shiny black head capsules and a black thoracic shield on top of the segment just behind the head.
The leaf structures created by this leaf-tier caterpillar tend to occur near the tips of plant stems and may be very obvious. While the structures may look very odd, the damage appears to cause little harm to the overall health of its namesake host despite noticeably reworking normal leaf architecture.
Caterpillars develop rapidly in the spring, and pupation usually occurs in southwest Ohio in early to mid-June. The beautiful, tiny native moths that emerge are grouped with other diminutive moths in a non-taxonomic category known as “microlepidoptera.”
It’s reported that the moth only has one generation per year, with pupation occurring in the soil beneath infested plants. In that scenario, the moths spend the winter in the pupal stage. However, I have taken numerous pictures in southwest Ohio of pupae in the leaf structures, or empty pupal skins hanging out of the structures in early to mid-June. This implies that there may be a second generation. I’ve never observed this because I just assumed there was one generation. However, I plan to look this season.
The Wasps (Winged Wolves with a Sweet Tooth)
Notable members of the wasp family, Vespidae (order Hymenoptera), in Ohio include Baldfaced Hornets (Dolichovespula maculata), Yellowjackets (Vespula spp.), and Paper Wasps (Polistes spp.). They all have common lifestyles and life cycles.
Only one of these wasps has “paper” in its common name. However, all of these vespids use their powerful mandibles to grind up weathered wood and other plant fibers to mix with their saliva and extrude a paper-like pulp used to construct their nests.
The paper nests of baldfaced hornets and paper wasps are above ground and easy to spot. Yellowjackets commonly hide their nests below ground or in attics, behind walls, or in other structural voids.
All of these vespids only use their nests for a single season. Queens and drones (males) are produced at the end of the season. The queens and drones leave the nests, mate, and the queens seek protected sites to spend the winter. The sterile workers left behind slowly succumb to freezing winter temperatures, no doubt humming a sad dirge.
The overwintered mated queens emerge in the spring to begin constructing new paper nests. They work alone in this endeavor and not only require fibers for paper, but also protein to develop their eggs and carbohydrates for energy. This is where we can start connecting some dots.
The OGIA/OSU Extension Diagnostic Walkabout participants came across the empty Hydrangea Leaftier structure pictured below. Note the huge hole presumably made by a predator.
Although a bird may have made the hole, it’s also possible that an overwintered wasp used its powerful mandibles to tear through the leaf structure to extract the caterpillar meat morsel. This predatory behavior isn’t just practiced by the queens. The workers that appear later in the season harvest soft-bodied insects such as caterpillars and sawfly larvae, grind up the bodies, and feed the high-protein meat-mush to the legless, helpless wasp larvae in the paper nests. Collectively, they are significant predators.
Where do the wasp queens and workers get carbohydrates for energy? They visit flowers. Shortly after the Diagnostic Walkabout, I photographed the baldfaced hornet queen pictured below busily visiting the small flowers of buckthorn to drink nectar and possibly consume pollen. The plant wasn’t labeled, but given its growth habit and park location, It may be Rhamnus frangula 'Ron Williams', which is considered less likely to escape landscapes to disperse into the wild.
Connect the Dots: A Twofer
It’s unlikely the baldfaced hornet I observed visiting the buckthorn flowers was also the culprit that snatched the hydrangea leaftier caterpillar. That would be too coincidental. Besides, it could have been a bird.
However, it’s well documented that baldfaced hornets, yellowjackets, and paper wasps are serious predators of soft-bodied insects. The image below shows a bagworm bag ripped open by a predator, which was most likely a baldfaced hornet, given the close proximity to two hornet nests.
It’s also well documented that predator wasps may be fueled by nectar. Of course, the wasps don’t hold a candle to bees (e.g., family Apidae). Still, predatory wasps are rightfully considered plant pollinators.
In other words, vespids provide a twofer: They are both predators and pollinators. This means an effective long-term pest management strategy is to simply plant flowering plants that provide nectar.
A scientific paper published in 1976 showed that the parasitoid wasp, Itoplectis conquisitor (family Ichneumonidae) accounted for almost 76% of the parasitism observed on Common Bagworms (Thyridopteryx ephemeraeformis) in the study. As with many enemies of other insects, this parasitoid wasp commonly visits flowers; it’s a pollinator.
A study published in 2005 showed parasitism rates of I. conquisitor exceeded 70% in bagworm-infested plants that were next to a central flower bed, but less than 40% in infested plants with flower beds further away. Thus, an effective insecticide-free long-term bagworm management strategy is to plant flowering plants that attract pollinators, including parasitoid wasps.
Final Thoughts
Damage by hydrangea leaftier moth caterpillars to the namesake host seldom progresses beyond the "oddity category." This is important because the leaf structures shield the caterpillars from direct exposure to a topical insecticide, and there is no data on the efficacy of systemic insecticides. If caterpillars or pupae are found within the structures, they can be digitally dispatched through death by squeezing.
On an ecological note, according to the literature, leaf shelters constructed by this and other lepidopterous larvae play an important role in forest ecology by sheltering spiders and other arthropods. Indeed, it’s common to find earwigs and spiders sheltering in the hydrangea leaf abodes before the caterpillars vacate the premises. The spiders will co-exist with the caterpillars without killing their benefactor.
I first observed the peculiar leaf structures produced by the hydrangea leaftier in 2010 in Spring Grove Cemetery and Arboretum, Cincinnati, OH. It's fitting, because another Cincinnatian, Annette Frances Braun (pronounced “Brown”), older sister to noted botanist and ecologist Emma Lucy Braun, was a leading authority on microlepidoptera with two moth species named in her honor: Argyresthia annettella and Glyphipterix brauni.
In 1911, Annette was the first woman to earn a Ph.D. from the University of Cincinnati. Her younger sister was the second. Both were Cincinnati natives and are buried side by side in Spring Grove in the shadows of the celebrated “Spring Grove White Oak” (Quercus alba) in section 101.
Selected References
Ellis, J.A., Walter, A.D., Tooker, J.F., Ginzel, M.D., Reagel, P.F., Lacey, E.S., Bennett, A.B., Grossman, E.M. and Hanks, L.M., 2005. Conservation biological control in urban landscapes: manipulating parasitoids of bagworm (Lepidoptera: Psychidae) with flowering forbs. Biological Control, 34(1), pp.99-107.
https://doi.org/10.1016/j.biocontrol.2005.03.020
Grissell, E. E. (2003). Hornets and Yellowjackets, Vespula and Dolichovespula spp.: EENY-081/IN238, 5/1999. EDIS, 2003(14).
https://journals.flvc.org/edis/article/view/108990
Sheppard, R.F. and Stairs, G.R., 1976. Factor Affecting the Survival of Larval and Pupal Stages of the Bagworm, Thyridopteryx Ephemeraeformis (Lepidoptera: Psychidae). The Canadian Entomologist, 108(5), pp.469-473.
