Description and Biology
The oak vein pocket gall midge, Macrodiplosis quercusoroca, is a tiny, mosquito-like fly so small that it is likely overlooked. They are about 1/8 inch long. Female midges lay their egg in new spring leaves that are just unfolding. After the eggs hatch, extremely small maggots begin feeding on lateral and mid-veins. Secretions by females or newly hatched maggots cause infested leaves to form elongate, pocket-like swellings on the lateral veins and mid-rib of pin oak leaves that eventually surround each maggot. Full-grown larvae are white and approximately 3/32 inch long. By mid-spring to early summer mature maggots emerge from the gall and fall to the ground where they spend the fall, winter, and next very early spring. We have one generation per year in North Carolina.
Oak vein pocket gall midges infest the the undersides of the leaves of red oaks such as red oak, southern red oak, pin oak, and water oak. Numbers of these midges in some years can be severe enough to cause noticeable twisted and distorted leaves when just about every leaf on a tree becomes infested.
If there is a need to control oak vein pocket galls on a tree, spring time would be the best time to do it. Theoretically, sprays applied early in the spring should the midges before they can inject their gall-causing secretions. Little research has gone into the insecticidal control of pocket galls, and most entomologists discourage trying. Insect populations vary greatly from year to year and place to place. It is highly likely that these galls will be much less noticeable next year due to parasites, predators, and diseases. One entomologist recommends, "Just live with it and enjoy the pleasures of one of nature’s most fascinating insect-plant interactions."
- Biology, Ecology, and Evolution of Gall-Inducing Arthropods (2 Vols.). A Raman et al. 2005. CRC Press, 780 Pages. (I haven't seen this reference, but it ought to be good at $176.00!)
- Gall insects most active in the spring. Merchant, M. 2014 (update). Texas A&M, AgriLife Extension, Insects in the City.
- Galls. Conrad, J. No Date. Backyard Nature Home.
- Oak Vein Pocket Gall Midge. Cloyd, R. 2020 (update). Kansas State University Extension Entomology.
- Extension Plant Pathology Publications and Factsheets
- Horticultural Science Publications
- North Carolina Agricultural Chemicals Manual
For assistance with a specific problem, contact your local Cooperative Extension center.
This factsheet has not been peer reviewed.
Publication date: April 12, 2020
Revised: April 12, 2020
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