Nature Ramblers: July 2022

Ramble Report July 21, 2022

Leader for today's Ramble: Bill Sheehan

Author of today’s Ramble report: Bill Sheehan

Number of Ramblers today: 20

Today's emphasis: Galls

It was a rainy morning in Georgia, so the Ramblers gathered in the Garden Room on the lower level of the Visitor Center for an excellent presentation on galls by Bill Sheehan – what they are, how to find and photograph them, and how to participate in citizen science efforts to document them. Bill also brought in several gall specimens from Garden trees and shrubs and demonstrated how to examine and dissect them using a dissecting microscope. What follows are Bill's Powerpoint slides and his commentary.

One of the more interesting people who studied galls was Alfred Kinsey. His collection of over 5 million gall wasps is one of the largest insect collections in the American Museum of Natural History. He later applied the same “big data” approach to the study of human sexuality, resulting in groundbreaking (and blockbuster) books on male and female sex sexuality in the early 1950s. This is, of course, not to say that if you take up the study of galls you’ll wind up studying human sexuality!

My objectives today are to describe what galls are, convey the range of gall diversity, and describe some of the tools I’m using to learn about galls. I’m still at an early stage, having gotten serious about them only this year.

Some galls are large and hard to miss. You’ve probably seen examples made by the Wool Sower Gall Wasp and the various Oak Apple gall wasps. Also common are those of the Goldenrod Stem Gall Fly, the Cone Gall Aphids on witch hazel, or by some large fungi like Cedar-Apple Rust (after rain on junipers), or perhaps the galls found on Horse Sugar.

But most are much smaller, like these galls made by tiny flies called gall midges.

Plant galls are abnormal plant growths caused by a wide range of other organisms that hijack the host plant’s physiology. They typically concentrate nutrients for the benefit of the gall-making organism, and, especially with insects and mites, provide shelter for developing youngsters. Insect galls are induced by chemicals deposited by the insect or mite mother along with the egg, or by chemicals secreted by the larva after it hatches. In the Goldenrod Leaf Gall, spores of a fungal symbiont are deposited with the egg by a gall midge. It is the fungus that guides growth of the gall structure and provides food for the developing young.

Many different kinds of organisms can induce galls on plants, including bacteria, fungi, nematodes, mites, and insects. Insect-induced galls have the most complex and varied structures. There is speculation that some insects may incorporate DNA from bacteria or viruses to provide the instructions that result in the host plant growing a particular gall structure (specific for each species). The author of a 2019 paper provides such speculation. Perhaps analogously, Mike Strand at UGA has demonstrated how the two main lines of hymenopteran parasitoids (wasps that lay their eggs on or in the bodies of other insects) incorporate viral DNA to overcome the immune responses of their insect hosts.

Some of the most common insect gall-makers include gall wasps, gall midges, certain moth larvae, and aphid relatives. Wasps, flies, and moths have larvae specialized for feeding that look entirely different from the winged adults. Aphids and other true bugs, on the other hand, have young with legs and look like adults without wings.

This is an interesting gall that I have found many times at my house. While most insect gall-makers hijack plant physiology, this midge causes a crust fungus to make a gall for it – something quite unusual in the world of insect galls. The fungus is the toothy thing feeding on a dead Water Oak branch, and the little bumps are midge galls. Inside the midge gall chamber is white material which is probably a different fungus imported by the gall midge to provide food for the developing larva. Bottom line: an animal makes a gall on a fungus which is feeding on a plant (dead oak branch) and the insect brings along another fungus for food.

Leaf mines are similar to galls in that they are an enclosed space within a plant in which an insect develops. There was an outbreak of Solitary Oak Leaf Miners this spring around North Georgia, primarily on White Oaks but also on some other oaks. Many people were concerned (including ramblers, see this rambler report), but it’s unlikely that it has a lasting effect on the trees. For one thing, it’s most prevalent in edge areas, around houses and roads, much less abundant in the woods, and less prevalent higher up in trees.

I use three tools to learn about galls: a camera and two websites, gallformers.org and iNaturalist.org.

I created a project on iNaturalist called Galls of Clarke County, GA. It displays any observation of a gall-maker posted by anyone since January 2000. As of July 18 of this year, 48 observers had posted 360 observations of 125 species.

· Using the website www.gallformers.org/id, you can see all documented gall species in Georgia – or in all of North America. Since gall insects tend to be host specific, you need to start by specifying a host plant. Here are statistics for two of the most fascinating (to me) gall-making insects:

–There are 406 species of cynipid gall wasps documented on all oak species in Georgia.

–There are 62 species of gall midges documented on all hickories in Georgia.

Photo-document: You can use any camera but a smartphone streamlines things because every photo has geocoordinates and a timestamp encoded in it (you can add them manually on iNaturalist), and you can upload directly to iNaturalist from a smartphone. Some tips to make observations of maximum usefulness:

Learn how to take closeup shots of tiny galls (next slide)

Take a couple of photographs of the host tree to support your host plant ID. Accurate host tree identification is critical. You’ll need it to ID your gall, and you could have host range extension or an undescribed species of gall-maker.
On at least one photograph include part of your hand or a fingertip for scale.
Take multiple photographs, crop them, and only upload the best ones.
Cut the gall open and photograph if possible.
Buy a dissecting microscope to see the world from an insect’s eye view!

A key tool I have found for photographing insects and other small things is the auto-focus lock function. On a smartphone, aim at anything with similar lighting (your arm, a tree trunk) at a distance of several inches, and when it comes into focus press the screen until AF LOCK or a padlock symbol appears. Then point at your subject from the same distance, and shoot.

Gallformers.org: Before posting your photos to iNaturalist, go to www.gallformers.org/id to try to get a gall-maker ID – at least to family. First, add the host plant species, or at least host genus (e.g., oak or hickory). You will see all the gall species that have been recorded from those host plants. For White Oak, it is 118 gall species. You can narrow that down by providing the gall family (if known), the location of the gall, or other features (like hairy). Then scroll down the page and see which gall most closely resembles what you have.

iNaturalist: Finally, go to iNaturalist, either on your smartphone or your home computer or tablet. You’ll need to set up an account, which is free. Upload your photos, putting your best one first, since that will be the one displayed on the observations page. It helps greatly to provide the best gall-maker name you can because it makes it easier for other interested people to find it. If you leave the name blank, iNaturalist will display “Unknown” and no one will find it. iNaturalist uses machine learning to provide name suggestions but that doesn’t work very well for non-charismatic tiny things like most galls. This is why it is good to have at least a family name from gallformers.org. The power of iNaturalist is that it engages naturalists all over the world with similar interests. You can tag people by putting their iNaturalist screen name preceded by @ in the comment field of an observation. When I am uncertain, I often tag @megachile, one of the young hotshots behind the gallformers.org site. Use of iNaturalist is a topic for another rainy day!