Well, it’s a nice problem to have: too many assignments. First is expanding the short Opie post from yesterday, but also working on this one about stuff in autumn….
GOLDENROD GALL BALL. Knock, knock, yes someone is home, snug in this goldenrod ball gall. A gall is an abnormal outgrowths of plant tissue caused by parasites, insects or mites.
A fruit fly causes this particular gall. Each gall contains a single plump larva, which overwinters Inside the gall.
The quarter-inch-long larva slows its metabolism and utilizes glycerol as an antifreeze. If undisturbed by predators, the larva tunnels to just short of the surface, goes back to the chamber to form a pupa, and emerges in a few weeks as an adult fly able to pop through the thin-walled porthole, clearly visible in the photo.
After all this, the adult Goldenrod Gall flies do not eat and last only about 10 days, living only to mate and produce a new generation of gall-causing young.
And here’s a ton of background. I should point out that these are VERY common so if you’d walking through any grassy field that has goldenrods there if you just look you are bound to see a bunch of them.
Goldenrod Gall Fly Life-Cycle
The goldenrod gall fly (Eurosta solidaginis) is a common and widely distributed insect found coast to coast in the central part of North America. The adult flies emerge from their galls in late spring. In Manitoba they emerge mid to late May, or even early June. Remember, the goldenrod stems have to have emerged first. Adult gall flies are small (about 5 mm), clumsy and are poor fliers. (They have difficulty righting themselves if they fall on their backs!) They do most of their traveling by walking.
Adult flies only live about 2 weeks, during which time they mate and the females lay their eggs. They deposit them at the tip of the emerging goldenrod stems, and they are pretty choosy about which goldenrod species they use. Of the many different kinds of goldenrods found in Manitoba, the flies are known to use only two, graceful goldenrod (Solidago canadensis) and late goldenrod (Solidago gigantea). The former of these two, graceful goldenrod, is by far the most common host for the gall flies in Manitoba.
The female may lay several eggs per stem, but each stem tends to end up with only one larva in one gall. In about 10 days the eggs hatch and the larva burrows down into the plant stem. The larva’s chewing and the action of its saliva, which is thought to mimic plant hormones, results in the production of the galls which provide the larva with both food and protection. There they feed and grow, passing through 2 larval stages. The 3rd stage larva reaches its full size by late summer; this is the stage that will over-winter and is freeze tolerant. One of the last things the larva does is to excavate the exit tunnel that it will use to escape from the gall as an adult the following spring. The larva scrapes out a tunnel from its central chamber right to the edge of the outer wall of the gall, leaving only the plant epidermis (skin-like layer) remaining. It doesn’t eat the material it scrapes out, which accounts for the debris usually found within the central chamber of the gall.