04 February, 2023

Discovering an Unknown Andricus sp. On Crimson Spire Oak

Some of the most enjoyable days at work start with, "Hey Andrew, I took a photo of this weird bug, do you know what it is? Do you have time to go take a look at it?" The deal even sweetens when I find collecting jars full of insects to ID on my desk!

As many people know, I work at a Landscaping company in Colorado where my expertise in Entomology is regularly put to the test. It was a typical Colorado April morning when my boss showed me some images of an Oak tree in distress. Large stem swellings and abnormal growth. For those of us in the industry this was obvious signs that a gall forming insect was the culprit. The abnormal growths gall forming organisms create can be beautifully bizarre and intrigue the interest of any onlooker but rarely require removal or intervention of any kind. As the creeping yellow green finger galls produced by Eriophyid mites on Linden leaves or the bulges of the Poplar Twig Gall Fly on Aspen may make for fun conversation topics, they are not familiar with the spray of pesticides. A vast majority of galls are considered non-damaging and aesthetically disturbing at most. It can also be difficult to properly target organisms protected by the galls they form. So what's the big deal? Why would anyone care about a gall forming on an Oak?

There are over 1500 species of gall forming organisms with insects and mites making up the majority. Oaks have been well documented to play host to numerous gall forming insects, so hearing news of an Oak with galls was not a surprise. What was a surprise; three hybrid Oaks (Q. robur x Q. alba) lit up brighter than Clark Griswolds house with galls. The Q. robur x Q. alba hybrid Oak, 'Crimson Spire', is marketed as resistant. Hybrid trees odd chemical signature is typically considered non-ideal compared to their native relatives. Upon further inspection, gall formation was so intense and dense that it had caused branch dieback and bud abortion to any portion of the branch above the galls. It can be hard to estimate the percentage of branches affected, but the average was certainly north of 60% for each tree. The homeowner mentioned that two other tree care companies came to have a look and left with the same diagnosis: 'It's a gall. It's aesthetic. Let it go.' Being the Entomologist that I am, I was a bit more curious than that.

Exit holes were not yet present and the homeowner allowed me to take a few cuttings home with me. Although my absolutely amazing and supportive wife encourages my insect adventures, she wasn't overly thrilled when a few weeks later we had dozens of minute wasps flying around my office. I was able to capture images of the adult female under the scope and begin the identification process. Whilst I searched for possible culprits I ran across just how many gifted, intelligent and dedicated gall experts there are out there. Adam (@megachile) has been an inexhaustible resource and his work producing (https://gallformers.com/) is exceptional. Adult specimens were sent to Miles (@mileszhang) for ID and his assistance and expertise has been greatly appreciated. I am hoping I can find additional adults this spring and continue to track the distribution of this seemingly new gall along the Colorado Front Range.


Posted on 04 February, 2023 05:06 by entoandrew entoandrew | 0 comments | Leave a comment