7: Plant Galls: Protection and Food for the Young Check Access

When certain insects sting a plant part and proceed to lay an egg into it, a local plant tumor, called a ‘gall’, is formed. Plant galls exhibit a great diversity of shapes, sizes, and colors, with each species of gall-making insect causing a different type and shape of gall, and on a specific plant. A few gall-inducing insects cause great damage, like the grape phylloxera (Daktulosphaira vitifoliae) or the rice gall midge (Orseolia oryzae). Growth of plant galls can also be caused by mites, fungi, viruses, or bacteria. Some galls have been used as dyes, for making inks, and for medicinal purposes. Galls, especially oak galls, have a high content of tannins. Some galls are edible fruits as in the case of figs (Ficus sp.). Different species of Ficus have different pollination mechanisms, but all require a specific species of wasp for pollination. The exact mechanisms of the induction and growing of galls are still largely unknown. It has been suggested that secretions from the insect, when it stings a plant part and lays an egg into it, trigger the local production of plant hormones or plant growth factors, like auxins and cytokinins.