Plants seldom have only one problem. The truth behind this axiom can muddy diagnostic waters on multiple levels, including the risk of failing to discover one plant problem by remaining too focused on another.
During the OGIA/OSU Extension Diagnostic Walkabout held earlier this week in Spring Grove Cemetery and Arboretum, we observed a Shingle Oak (Quercus imbricaria) festooned with a fine collection of Horned Oak Galls produced under the direction of the cynipid gall-wasp, Callirhytis quercuscornigera. The “horns” that are responsible for the gall’s common name were rising to the surface, which is a significant stage in the gall wasp’s life history. The walkabout became a standabout. You can read about the galls in my BYGL Alert titled, “Horn Rise,” [ https://bygl.osu.edu/node/2616 ].
It wasn’t until I returned to the tree after the walkabout to take pictures of the galls (you can never have too many) that I discovered that we had been so focused on the galls that we had completely overlooked Oak Treehoppers (Platycotis vittata) nymphs milling about on the galled oak stems. We had missed a great diagnostic opportunity.
This native treehopper is one of the more colorful members of the Membracidae family. It also practices a level of maternal care that’s unusual for a non-social insect.
The nymphs appear in aggregations that may number over 100. They have an overall shape that’s vaguely suggestive of a miniature horseshoe crab.
Their abdomens are covered in black and white bands with red highlights on the lower edges. It is believed the color motif warns predators (= aposematic coloration) that the nymphs taste bad, although I’ve never taste-tested to find out if it’s true.
Oak treehopper adults can present an identification challenge owing to having both “horned” and “hornless” body forms, and two different color forms. Indeed, the diversity of their appearance can make them look like they are entirely different species.
The “horned” and “hornless” body forms center on the pronotum. The pronotum is the first thoracic segment located just behind the head in an insect’s general body plan. The pronotum on treehoppers is unusual. It typically covers the head, as well as the rest of the thorax, and extends over part of the abdomen.
As shown in the image above, the pronotum of some oak hopper adults features a horn-like protrusion. Others have a blunted pronotum, as shown in the image below.
The adults may also appear in two different color forms: striped or mottled. Both color forms sport a multi-colored motif, with the striped form having red longitudinal stripes on a gray background and the mottled form having yellow, reddish-yellow, or orange spots on a gray background. However, research has shown that the color forms as well as the pronotum ornamentation may change over time within the same aggregation.
Research conducted at Wilmington College (Wilmington, OH) showed that the oak planthopper has two generations per year in Ohio. The spring generation arises from overwintering females that use their sharp ovipositors (ovi = egg; positor = deposit) to insert eggs into tree stems, similar to the way periodical cicada (Magicicada spp.) females lay eggs into tree stems. However, the treehopper damage is much less severe.
The females remain with the eggs and then the nymphs to guard them against predation as the nymphs develop through 5 instars. Researchers observed females driving off predators, including formidable paper wasps (Polistes spp.). If that didn’t work, the females would sacrifice themselves to the jaws of doom in an effort to save their young. Oak treehopper nymphs should remember to celebrate Mother’s Day.
The colonies I observed included a protective “mother” and nymphs at various stages of development. Eventually, there will be nothing but new adults that pass through a brief aestivation, a type of dormancy practiced to escape the heat of summer. Then they mate, and the females will lay eggs that give rise to the “fall generation.” It’s the females that arise from the fall generation that will overwinter and give rise to the spring generation next year.
Oak treehoppers are native to a wide swath of the United States; however, the literature notes that their range does not extend north of the 40th Parallel. Of course, that may be changing with our changing climate. The hoppers may be found on deciduous and evergreen oaks.
Although the treehopper females produce stem damage when they lay their eggs, the damage is inconsequential, causing no harm to the overall health of their oak hosts. The same is true for the feeding damage by both the adults and nymphs. Both insert their piercing-sucking mouthparts into the stems to suck juices from the phloem and perhaps the xylem; however, they do not create enough damage to produce stem dieback. Besides, it’s rare to find more than a few treehopper aggregations on a single tree. Consequently, management strategies are not required.
Selected References
Lin, C.P., 2006. Social behaviour and life history of membracine treehoppers. Journal of Natural History, 40(32-34), pp.1887-1907.
Lin, C.P., Cast, M.S., Wood, T.K. and Chen, M.Y., 2007. Phylogenetics and phylogeography of the oak treehopper Platycotis vittata indicate three distinct North American lineages and a neotropical origin. Molecular Phylogenetics and Evolution, 45(2), pp.750-756.
Wood, T.K., 1975. Defense in two pre-social membracids (Homoptera: Membracidae). The Canadian Entomologist, 107(11), pp.1227-1231.
Wood, T.K., 1976. Biology and presocial behavior of Platycotis vittata (Homoptera: Membracidae). Annals of the Entomological Society of America, 69(5), pp.807-811. https://doi.org/10.1093/aesa/69.5.807
Wood, T.K., Guttman, S.I. and Taylor, M.C., 1984. Mating behavior of Platycotis vittata (Fabricius) (Homoptera: Membracidae). American Midland Naturalist, pp.305-313.
