Participants in last week’s OSU Extension/OGIA Diagnostic Walk-About held in Spring Grove Cemetery and Arboretum in Cincinnati came across an aggregation of Oak Treehopper (Platycotis vittata) nymphs on a mature white oak (Quercus alba). This treehopper is one of the more colorful members of the Membracidae family and behavioral studies have revealed 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.
Oak treehopper adults may or may not have a distinctive pronotum (= first thoracic segment) that covers the thorax and part of the abdomen to the rear and is formed into a horn-like structure at the front. Pronotum ornamentation is common among treehoppers.
The adults may also appear in two different color forms: striped or mottled. Both color forms sport a multi-colored motif with the stripped form having red longitudinal stripes on a gray background and the mottled form having yellow to reddish-yellow spots on a gray background. However, research has shown the color forms as well as 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 guarding 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. It would be fitting for oak treehopper nymphs to celebrate Mother’s Day.
We saw newly emerging nymphs last week that were passing from one instar stage to the next. We could tell they were immature because they still had “wing pads.”
However, I revisited the tree this week and found that new adults were beginning to emerge. The new adults will pass through a short aestivation which is 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 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.