Plant galls that are produced by insects and mites are now becoming very evident throughout Ohio. While some galls may damage their host plants, the vast majority cause no appreciable harm. Indeed, students of pest-host interactions view insect and mite galls with a certain sense of wonder. Following are a few gall-points that may help non-gall-enthusiasts to fully appreciate these fascinating plant growths:

• Most insect and mite galls consist entirely of plant tissue grown in a very specific way under the direction of a gall-maker. The gall-maker exudes chemicals that mimic plant hormones to turn plant genes on and off at just the right time to direct gall growth.

• The galls can only form on tissue that is in the process of differentiating. Thus, leaf galls grow as leaves expand. Galls cannot form from plant cells that have stopped dividing.

• Insect and mite galls are usually so specific that the gall-maker can be accurately identified to species based entirely upon the gall structure, without benefit of actually observing the gall-maker.

Some notable galls currently being found in Ohio include several oak galls that are produced by tiny, gnat-like wasps in the family Cynipidae. On white oak, these include: the bristly, descriptively named SPINY OAK GALLS formed on the upper leaf surface by Acraspis prinoides; the shaggy-looking HAIRY OAK GALLS produced by A. villosa; and the grape-like CLUSTERED MIDRIB GALLS formed on the lower leaf midrib by Cynips dimorphus.

Cynipid wasp galls found on red and pin oaks include: the aptly named OAK APPLE GALLS produced by Amphibolips confluenta that look like tiny apples growing off stem tissue; the knobby club-like HORNED OAK GALLS produced by Callirhytis cornigera that may be adorned with short, protruding horn-like structures. Of the over 700 galls found on oaks, very few cause appreciable harm to their hosts. Horned oak galls are an exception. Opening these woody galls will reveal the jumbled mass of disorganized stem tissue that is responsible for disrupting vascular flow beyond the gall, causing dieback of twigs and branches.

The handiwork of several gall-making mites in the family Eriophyidae may also be appreciated. These include: the light-green to reddish-green, finger like MAPLE SPINDLE GALLS on the upper leaf surface of sugar maple, caused by the eriophyid Vasates aceriscrumena, and on the upper leaf surface of black cherry, caused by the "cherry-ophyid mite" Phytoptus cerasicrumena.