When we visited the South Oslo Riverfront Conservation Area (SORCA) on 6-18-2002 to check out the blooming Florida butterfly orchids, we also saw this collection of small, round galls growing on Chapman oak (Quercus chapmanii). These adorable galls are the handiwork of a tiny gall wasp (Trigonaspis polita). These galls are the asexual (agamic) stage. More about that later.
These detachable, hairless globular galls can be brown, orange, yellow, red, or some combination thereof in color. You will find them on the upper side of the leaf, the lower side of the leaf, and on the leaf midrib. ID was made possible by the gallmakers.org website.
Gallmakers can be fungi, nematodes, or from 6 different insect orders: Diptera (flies), coleoptera (beetles), lepidoptera (butterflies/mothes), thysanoptera (thrips), hemiptera (ttrue bugs), and hymenoptera (bees/wasps,/ants). Gallmakers have an allegiance not only to a particular plants species (or related species) but to a particular part of the plant: Leaves, stems, roots, flowers, …
The insect gallmaker induces the plant to produce a tumor-like growth that is nutrient rich and serves as a microhabitat in which larvae feed, develop, and pupate. The gall provides nutrition, protection from environmental conditions, and a refuge from predators (sometimes).
Trigonaspis poilita, our gallmaker, is a cynipid gall wasp, a species rich and phenotypically diverse group that is thought to be responsible for ~70% of oak galls. When a gall wasp oviposits an eggs (or eggs), the egg is accompanied by a maternal secretion from its venom gland, which initiates gall formation.
The annual life cycle of this wasp is complex, alternating between a sexual and asexual generations. Males and females mate in the sexual generation. The galls, the asexual generation, produce males and females parthenogenetically. Check out the exit hole on the right side of the picture below.