The Case of the Mysterious Mesosa Longicorn Beetle
By Bekka Brodie
It was a beautiful, sleek, black beetle with long antennae. Immediately, I knew it was different than any other longicorn beetle I had seen, but its identity eluded me.
Solving mysteries may be “elementary” for Sherlock Holmes, but for entomologists, trying to identify an unknown insect requires more than careful examination of trace evidence to reveal information about a mystery insect — especially when there are more than 400,000 different species of beetle worldwide! Identification requires a systematics key, careful examination of the beetle’s habitat, and a review of the scientific literature. And in this case, a team of entomologists from all over the world.
I discovered the mystery beetle while trapping deep in a sub-Mediterranean forest of the Iron Gates Natural Park in Southwest Romania. I had been checking traps for a month and a half as part of the Romanian beetle project, an effort to survey endangered, threatened, and poorly understood longicorn beetles (Family: Cerambycidae). In total, I managed to trap five of the mystery beetles, and each of them was discovered in mixed forests tree stands made up of Oak, Beech, Maple, and Linden.
The mystery beetle was 15 mm long, all black, and the first pair of wings (the elytra) appeared naked, lacking little hairs (also known as pubescence). It had an unarmed neck with no prothoracic spikes, and the first and bottom antennal segment was thick with a sharp edge. Using a Romanian key (with Google translate), an outdated English key, and the Internet, the latter two characteristics should have placed it in the genus Mesosa, but there are only two species known in Romania, the eye stain longicorn (Mesosa curculionoides) and the white-clouded longicorn (Mesosa nebulosa). This “Mystery Mesosa” looked much different than those two species!
To assist with identification, I got in touch with the Romanian Longicorn expert, Rodica Serafim. Rodica (although retired) works at the National Natural History Museum Grigore Antipa and was happy to assist with the Mystery Mesosa (in addition to confirming the identity of 40+ beetle species I surveyed that summer). Rodica deduced that it did indeed belong to the genus Mesosa. In fact, she said it “looked like a white-clouded longicorn (Mesosa nebulosa) but that it had lost its pubescence.” Since neither of us could understand how a beetle could loose its pubescence, we were convinced that it was NOT from Romania. The Mystery Mesosa was either a new species or an introduced species. I was intrigued!
I needed to pool all of the resources available in order to identify the Mystery Mesosa. Usually, because I’m from upstate New York, my favorite resource is BugGuide.net, but it is mainly for the United States and Canada. I had to locate European and international resources (like Cerambycidae and Cerambycidae.eu) and use online social networks (Twitter and Facebook). First, I tweeted about the beetle, but got nothing. Then I posted to the Entomology and Cerambycidae (Longicorn beetle) groups on Facebook. Although many members of the Entomology groups “liked” my photographs and my plea for information, I still wasn’t able to collect any leads on its identity.
Then I turned to the international community of entomologists on the Entomo-L listserv and, finally, received a response from Doug Yanega, a taxonomist at the Entomology Research Museum at the University of California, Riverside. Doug gave me some good advice about the beetle’s characteristics and suggested that maybe it was not really a Mesosa because there are other beetles with similar characteristics (e.g, the tribe Monochamini). Still, he was stumped because he was unaware of anything similar that lacked pubescence, and every species he knew of had some sort of patterning. In fact, the mystery beetle was like none of the beetles he was familiar with! Unfortunately, Doug did not have any keys to identify Old World longicorns, but he referred me to a colleague, Francesco Vitali, an entomologist at the Musée national d’histoire naturelle de Luxembourg.
After hearing from Doug, I felt certain that I had a mystery beetle but was uncertain of whether it was a mystery Mesosa. So, I contacted Francesco Vitali, and he was happy to help! He noted that my specimen had characteristics specific to the subgenus Aplocnemia and that Mesosa nebulosa was the most probable candidate. He compared my macrophotos with specimens in his collection and observed no structural differences, with the exception of the missing pubescence. Nonetheless, he confirmed that the Mystery Mesosa was indeed the white-clouded longhorn beetle (Mesosa nebulosa) and that Rodica’s suggestion “that it was an old specimen which had lost its pubescence” was in fact true!
Still, how does a beetle lose its pubescence? I asked Francesco what was going on, and if the adult beetles were able to survive through the winter? He explained that this beetle can indeed overwinter, and that he has collected specimens as late as December. The overwintering adult beetle can survive for several months, generally until July. Hence, the pubescence can be damaged with age! This is contrary to the majority of longicorn beetles that I am familiar with in North America, where the pupae and larvae overwinter in trees and the adults persist only into the fall or until the weather becomes cold.
Overall, I captured 108 white-clouded longicorn beetles (approximately 50/50 males and females) with pubescence, and only five Mystery Mesosa — the ones without pubescence, which were all female. So, the female survival rate over winter was 10%. The successful overwintering increases its chances of finding a mate and producing offspring.
Thanks to a group of beetle experts from all over the world (Canada, United States, Romania, and France) I was finally able to correctly identify the Mystery Mesosa. It was in fact a white-clouded longicorn beetle (Mesosa nebulosa) that had emerged as an adult the previous summer, overwintered, and was out and about again this summer, exploring my traps in hopes of finding a mate. Just like in all of the great Sherlock Holmes mysteries, “once all the facts were in place, the theory made perfect sense.”
Bekka Brodie has research interests in insect communication, behavior, and conservation. The material presented here is part of her upcoming post doc at SUNY ESF as part of the Romanian Beetle Project supported by the Mohamed bin Zayed Species conservation Fund through the Association for Biodiversity Conservation (RO). Follow her on Twitter at @BbrodieS.