Stumbling Along the Path to Understanding
Charles Allen Haynes
July 11, 2022
This past week, getting over the virus, I needed to try normal for a while without overtaxing my reserves. (Didn’t have any). It’s always easy to turn to the natural world that goes on regardless. As I was walking slowly from the garage to the house I noticed single pecan leaves on the ground that had brown spots. On close examination the spots were raised, rough and seemed to have an “entry” point. I knew they were galls.
I took a leaf sample to the lab and photographed it top and bottom. I had been under the impression that galls are caused by a single order of insects… Hymenoptera, the tiny solitary wasps like the Ichneumonidae. In actuality there are several culprits that can cause galls including, the wasps, Midges, Gnats (Dipterans), Psyllids (Hemiptera: Plant Lice) and Phylloxerans (Hemiptera: similar to Plant Lice) and others.
I cut one open, halved in cross section. Using the stereoscope I picked out the fuzzy, non-descript interior, seemed like an unlikely resource for living material. Not so much. I have to constantly reassess scale as a factor in these kinds of investigations. I inadvertently cut the head off a thrip adult, (Thysanoptera) when I bisected the gall. I found it more or less by accident looking through the debris from the cutting. There appeared a bushy line of setae along the distal edges of clear wings atop a dark to black segmented abdomen. The wings are clear, veined and the overall insect is tiny, 1.2mm in length. I identified it as a thrip.* I was not sure I should find an adult thrip in a gall… coincidence, accident, maybe? Stay tuned…
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And there you are. Mature thrips can be expected inside galls in late July and August. Little early but… Now, to photograph the little rascals.
* Thrips belong to the family Thripidae. There are many species. Some are destructive to plants and others are beneficial as they eat aphids and other parasites.