Issue 1, April 16, 2010

Pin Oak Gall Larvae

We have received reports of large numbers of larvae being found under pin oak trees in the Springfield area. Based on somewhat sketchy information, these appear to be the mature larvae of a gall midge in the genus Contarinia. The larvae are whitish to yellowish and are likely to be about one-eighth inch long. This insect attacks the male catkins of pin oak, and the mature larvae drop to the ground. They burrow into the soil. It is assumed that pupation occurs in the soil, and that the adult flies emerge the following spring to attack the developing male flowers.

The larvae become noticeable on sidewalks and other paved areas where the larvae are unable to burrow into the soil. No control is recommended, other than the client sweeping up the larvae. Sweeping them off of the sidewalk, driveway, or porch onto the soil will aid the larvae in completing their development, which is acceptable. This is probably a native insect that will be controlled eventually by a predator, parasite, disease, or other natural enemy, although it may take two to three years for control to be noticed.

We received a similar report occurring in the St. Louis area under a silk tree or mimosa, Albizia julibrissin, in early April. Based on the photo provided, it is likely that this is another gall midge, but no reports were found in the literature to assist in its identification.--Phil Nixon

Phil Nixon

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