Last Thursday, Tom Macy (Forest Health Program Manager, Ohio Dept. of Natural Resources) sent a message noting that he is receiving reports from eastern and southern Ohio of mature yellow poplars (Liriodendron tulipifera) (= tulip-poplars, tuliptrees) that have failed to leaf out this spring; the trees were alive last season.
The reports primarily came from areas in the state that experienced the record-breaking drought last season, as well as high populations of native yellow poplar weevil (Odontopus calceatus). Tom noted that aerial forest health surveys last season revealed that the weevil was the number one damage-causing agent in Ohio’s forests, with 15,712 acres affected. U.S. Drought Monitor Map
The yellow poplar weevil is native to much of the eastern U.S., matching the native range of its namesake host. Aside from feeding on yellow poplar, the weevil also feeds and develops on magnolias (Magnolia spp.) and sassafras (Sassafras albidum).
The small (2/16" long), oval-shaped weevils range in color from black to brownish-black to reddish-brown and have deeply grooved wing covers (elytra). Although they are good flyers, the weevils often elect to fold their legs to "play dead" when disturbed; a defense strategy that is common among weevils.
Weevils are beetles with their chewing mouthparts located at the end of their snouts (rostrum). Yellow poplar weevils primarily target leaves where they consume the lower epidermis and leaf mesophyll, leaving behind the upper epidermis. Eventually, the thin epidermis dries out, turns brown, and is shed from the leaf to produce characteristic crescent-shaped or half-moon-shaped holes. Image 1 – Image 2
Although the yellow poplar weevil has one generation per season, adults feed on leaves twice during the growing season. The so-called “spring generation” of adults spends the winter in protected sites, such as in the duff beneath trees. They emerge in the spring to feed on buds, nascent leaves, and flowers. Heavy feeding damage can disrupt leaf expansion.
The spring adult females mate and lay eggs in leaf midribs. The weevil eggs hatch into white, grub-like larvae that feed as leafminers between the upper and lower leaf epidermis. The leafmining larvae may feed singly or in groups of up to 19 larvae to produce large blotch mines. Larval frass (excrement) is extruded as dark filaments that look like hair. Image 1 – Image 2
The so-called "summer generation" of adults arises from the leafmining larvae. Typically, there are a greater number of adults in the summer generation compared to the spring generation, meaning most of the leaf damage occurs in mid-summer.
Although larval leafmines are noticeable, the most serious damage is caused by adults, particularly the summer generation. Numerous feeding holes can cause leaves to wilt, turn brown, and die, making heavily infested trees look “burned.” Indeed, severe adult damage is sometimes mistaken for drought damage. Image
The summer generation adults drop from their hosts in mid-summer, usually sometime in July in Ohio, and crawl into the duff. They undergo a period of heat-related dormancy (aestivation) and then fall into a deep dormancy (diapause) for the winter.
One of the photos Tom sent also showed the mealybug-like larvae of the native Signate lady beetle (Hyperaspis signata). This native lady beetle is a scale specialist feasting on soft scales, including “cottony” scales, as well as felt scales. Their appearance indicated something else may be afoot on yellow poplars other than the yellow poplar weevil. Image 1 – Image 2
Last Friday, Jim Downs (OSU Extension, Forest Field Specialist) sent photos of mature yellow poplars near New Matamoras, Ohio, showing large trees that appeared to be either defoliated or dead. The photos were taken by T.J. Wells (OSU Extension, Washington County).
Close-up images showed the trees were not dead, but nascent leaves had suffered severe weevil feeding damage, disrupting their expansion. Additionally, some of the images also showed overwintered late instar tuliptree scale (Toumeyella liriodendri) and a Signate lady beetle larva; the two are no doubt connected. Image 1 – Image 2
As with all soft scales, the native tuliptree scale uses its piercing-sucking mouthparts to tap into phloem vessels. They withdraw large quantities of sap and expel excess liquid in the form of sugary, sticky “honeydew” that commonly becomes colonized by black sooty molds. The impact of the scale must be considered as we form a possible diagnostic picture.
It’s too early in the season to speculate on the outcome of the delayed leaf development on yellow poplars in eastern Ohio. It’s not clear if nascent leaves are being damaged by yellow poplar weevils before they can expand, or if tree health has been seriously compromised by, as Tom put it in his email messages, “the double-whammy” of weevils and drought, or perhaps the triple-whammy of the weevils, scale, and drought.
It's common for populations of native tree pests to rise and fall dramatically from year to year with periodical “outbreaks” followed by years with the pests being inconspicuous. Pest population roller coaster rides are driven by environmental conditions and the 3-Ps (Predators, Parasitoids, and Pathogens). Signate lady beetles are just one of the many predators that impact tuliptree scale populations.
We need your help with detecting and monitoring what’s going on with yellow poplar trees in eastern Ohio this season. If you observe large trees that are failing to leaf out and/or trees that are infested with yellow poplar weevils or tuliptree scale, please contact Tom Macy at: Thomas.Macy@dnr.ohio.gov