Gallmaking and Insects

Katherine N. Schick and Donald L. Dahlsten

University of California, Berkeley

Plant galls, which are abnormal growths of plant tissue that often resemble plant organs, can be induced by a wide variety of different insect species. The gallmaking insect stimulates the host plant through a complex chemical interaction so that the resulting gall is much more than a simple response to wounding or feeding damage. The precise gall form and position of the gall on the host plant is consistent and characteristic for each species of gallmaking insect.

Although cecidology, the formal study of plant galls, was initiated in 1679 with Malpighi's study of gallmaking insects, humans have admired and utilized galls for thousands of years. For example, Gallic acid (3,4,5-trihydroxybenzoic acid) was first derived from an oak gall induced by the cynipid wasp Andricus gallaetinctoriae. These galls have been commercially traded from source trees in the Middle East and the gallic acid derived from them has been used historically as a dye as well as an antiseptic astringent skin medication. Derivatives are used as photographic developers and the ink base made from these galls has been used to make permanent inks for such purposes as printing the U.S. dollar bill.

In 16th century England, the cynipid gall, Biorhiza pallida, was used for personal ornamentation. On May 29, the English parliament's official "Oak Apple Day," sprigs of oak leaves and gilded galls were worn to commemorate restoration of the English monarchy.

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