Galls – Intimate Interactions

Ansin Tract Conservation Area, Oslo Riverfront Conservation Area

Galls are a long-evolved interaction between a plant and a gall-maker. The gall-maker could be an insect, mite, bacteria, fungus, virus or nematode. Gall-makers generally are “tied” to one species of plants or a genus of plants and tend to be associated with a particular part of a plant — leaves, leaf buds, stems, flower buds, flowers, roots or branches. The plant reacts to the gall-maker with abnormal plant growth that can range from a simple indentation to a complex structure in which the gall-maker receives nourishment and protection.

The photo above of a stem gall on a sand live oak (Quercus geminata) was taken at the Ansin Tract Conservation Area on 8/5/2017. This gall also has been seen at the Oslo Riverfront Conservation Area (ORCA) on the south side of Oslo Road. Dr. Amanda Hodges, Associate Extension Scientist and Director, Doctor of Plant Medicine Program, University of Florida, identified this gall from the photo above as the handiwork of an oak bullet gall wasp, Disholcaspis sp. She is the co-author of Insect Galls of Florida, which can be purchased through the University of Florida Bookstore.

Gall wasps are quite tiny (.04 to .24″ bodies) and easily overlooked. They do not sting people.

Most gall wasps have a complicated life cycle that involves an alternation of an asexual (all female) generation and a sexual generation. These generations are structurally different and gall different parts of the host plant. This phenomenon is known as heterogeneity.

Disholcaspis quercusvirens likely is the culprit in the development of the multi-chambered (polythalamous) gall shown above. This stem gall is the handiwork of the asexual generation. The sexual generation is a bud gall. Disholcaspis quercusvirens also uses live oak (Quercus virginiana) and can become so prevalent in nurseries that the trees are “disfigured” by commercial standards.

Galls, to me, are like Christmas ornaments — decorations that remind us of the complexity and majesty of the natural world.