What galls you?

Cecidology is the study of plant galls, a new word for me but difficult to fit into a Scrabble game. It is not strictly a sub-discipline of botany nor zoology, as galls are created by viruses, bacteria, insects and mites but also fungi. Their appearance can reach the strange and bizarre, in the form of lumps, bumps and other growths. Usually galls form when the invader attacks living tissue of the host plant.

Generally the plants and their galls are considered to have a parasitic relationship, as the host receives no benefit and may be harmed. The invader may receive any combination of food, shelter and even protection. Any living tissue may be susceptible: roots, stems, leaves, flowers. Galls take on a recognisable form, which may even aid the identification of the all-former. They tend to be broadly or narrowly host-specific.

Galls may be open or closed. An open gall may result if the plant is attacked by invertebrates with piercing mouthpart. Aphids can cause the leaves they attack to curl in a gall around the insects. Closed galls develop when the attack is by the larval form of insects such as wasps or beetles, where the insect matures within before emerging.

Some of the commonly seen plants which are invaded by gall-formers in Nova Scotia are oak, willow, roses and goldenrods.

Willows see several small gall flies who produce the willow apple galls on the leaves. Sawflies (Order Hymenoptera) also inflict symmetrical galls on willow leaves. Tips of the twigs may host a variety of gall midges (dipterans).

Greatest diversity in insect galls is found in the oaks. For example gall-forming wasps, called cynipids (Family Cynipidae) attack many species, forming fancifully named gouty oak gall, oak apples and oak potato galls.

Gall-wasps also form the Mossy Rose gall and Spiny Rose Galls. Both are commonly seen in Nova Scotia.

Goldenrods are attacked by a variety of midges, on their leaves and stems.

What galls you? Have you seen any galls on plants in your yard? Why not snap a picture and send it. We will try to identify the plant and its attacker, with the help of a zoologist or two.

Gall on oak leaf, photo by Mary Macaulay