Glow in the Dark Tortoise Beetles
Southwest Yard & Garden by Dr. Marisa Thompson
with contributions from NMSU Extension Specialists Dr. Amanda Skidmore and Dr. Carol Sutherland (Entomology)
Curious and Curiouser: Tortoise Beetles Are Weird and Cool
 Adult tortoise beetle makes little holes on a tomato leaf in Albuquerque. Photo credit Gloria Lucero. |
Question: What kind of bug is this? It moves around the leaf like a Roomba vacuum cleaner.
- Gloria L., Albuquerque (question originally posted to the Facebook group “Growing Food in and around Albuquerque & Foraging Too”)
Answer: I saw these critters for the first time on my tomatillo and tomato plants at home this week. I had noticed irregular-shaped holes in the tomatillo leaves but hadn’t taken the time to investigate. I knew I’d had grasshoppers nibbling at leaf edges throughout the garden, but these were holes in the middle of leaves, not at the margins. The critters seemed to have a shiny, almost iridescent shell. When I looked closer I saw lots of smaller, creepier creatures on nearby leaves that looked more like mites or an immature form of a scale insect with a black helmet that it waved at me while I was taking photos. I was intrigued, and this was just the beginning.
Not a half-hour later, I mentioned them and their irregular Swiss cheesy holes to a co-worker at the NMSU Agricultural Science Center at Los Lunas, and he said he had similar holes on his chile plants, so I took a look. Sure enough, we found the same shiny, shelled insects and the helmet-wavers too. I assumed they might be a type of scale in both the larval and adult form until one startled me by spreading its shell into wings and flying away.
That evening Gloria Lucero posted a great pic of the same insect with a request for information in an Albuquerque gardening group on Facebook. Another person offered “tortoise beetle” as an identification. I shared my photos and immediately started a Google image search for “tortoise beetles.” The results were more entertaining than any Netflix show. Try it.
It turns out that tortoise beetles are known for getting crafty when making their shells and shields. Some make ornate armor out of plant tissues—search images for “palmetto tortoise beetle larva.” Many species, though, use their own feces to form bizarre protective structures. Yes, that’s right, those larval tortoise beetles I’d found were waving their poop umbrellas at me. Regular readers know I really love my job, and it’s precisely these kinds of experiences that invigorate me. And still, these tortoise beetles had more surprises up their…umbrellas.
I reached out to colleagues for more info on tortoise beetles in New Mexico and what I should do about them, if anything. NMSU Extension Integrated Pest Management (IPM) Specialist Dr. Amanda Skidmore offered, “In the Midwest, they are mostly found on wild Solanaceae plants [including potatoes, tomatoes, tomatillos, eggplant, and chiles] and not in the garden. The larvae are pretty crazy looking, and their ‘shell’ is actually their frass they are using as protection. The adults of this species even look like they have a tortoise on their backs. As for management in the home garden, hand-picking them off and dropping them in a bowl of soapy water is probably the best option. From what I have read, they will be focused on the leaves, not the fruit, so mature, healthy plants should be able to tolerate the feeding damage.”
Dr. Carol Sutherland, NMSU Extension Entomology Specialist and NMDA Entomologist, agreed that while both the adults and larvae may be making those holes, it won’t cause serious crop (or garden) damage. Dr. Sutherland added, “As far as I know, the tortoise beetles are long-time (but possibly part-time) residents of New Mexico. In the scientific literature, they were documented in the U.S. in the 1860s; otherwise, they’re supposed to be rather widely distributed in Central America and with ‘northward movement in spring.’ I’m asked about them every blue moon.”
That night, donning a headlamp and armed with a plastic cup of soapy water, I scanned my tomatillo and adjacent tomatoes for tortoise beetles, mostly nymphs.
Important side story: Last year, I saw a post about tomato hornworms being easier to find at night with a blacklight. Some arthropods fluoresce, or glow, under ultraviolet light (like from an electric blacklight). So I bought a $7 UV flashlight from a discount hardware store. It turns out not to be true for tomato hornworms—or not completely true. They are easier to find at night with a blacklight, but it’s not that they actually glow as much as their stripes reflect light, and it catches the eye.
Searching for tortoise beetle larvae that night, I wondered if they might be fluorescent too, so I got out my handy blacklight flashlight, and “OH, WOW! How cool!” SCROLL DOWN to see the video of these glowing "pests," more interesting details from Drs. Skidmore and Sutherland, and photos of other wild tortoise beetles from around the world.
Warning! UV light can damage exposed skin and eyes. As an undergrad lab assistant at UNM, I forgot to wear the protective welding mask one time when using a tabletop UV lamp. Seven hours later, I was in the emergency room with my eyes swollen shut and punctate erosion of my corneas. I was told that if the exposure had been longer, I could have permanently impaired my eyesight. After three days of meds and keeping my eyes closed all the time, my corneas healed, but the skin around my eyes peeled, like after a bad sunburn.
Extra Info!
1-minute video I took with a blacklight flashlight:
Dr. Amanda Skidmore suggested that we might be seeing them migrate to our gardens this year because of the high heat and drought.
We also think that we can probably expect to have more reported cases of tortoise beetles this summer because more people are growing vegetables this year (myself included) AND we're also spending more time in our gardens than previous years.
More notes from Dr. Carol Sutherland:
"If you want to be confused, this tortoise beetle is the one to confuse you. It’s taken more than a few years and several sources to find out what is going on with these critters.
Charidotella bicolor (Coleoptera, Chrysomelidae) is called the ‘golden tortoise beetle.’ When you see a live one of those in sunlight---it’s unforgettable. It looks like the metal gold, shining in the bright light…wow!So you collect it, it dies, and when you go to pin it for your collection, you find that your beetle has the shape of an old WWI Army helmet (very narrow, flattened ‘flange’ that goes all the way around the edges of the body). It's not metallic gold any more, instead it’s a somewhat shiny olive/tan color with a broad black X marking. How did that happen? Where’s my gold beetle?You’re not ‘losing it’ but have discovered something that took lots of extra research with high-powered equipment to explain it. These beetles can change their appearance---back and forth in real life apparently---depending on ‘mood’ and what they sense in their environment. But that kind of detailed observation requires a persistent curiosity and some luck. Far easier to be disappointed that your original golden ‘catch’ died and it faded to dull brown and black… and then forget about it.So what did some persistent scientists find? The hemolymph (blood) of these beetles apparently is reddish. As their heart works (not like ours), the reddish fluid washes throughout the body and even circulates through the thin layers of the forewings (elytra). The forewings are composed of 3s Collection. And of course, there are olive drab beetles with black Xs in that collection, behind that label.How about that? Pretty neat. So, yes, these beetles do occur in New Mexico, at least sometimes. They might move northward as spring conditions permit, but not to the same extent each year.The larva is another ‘trip.’ Millions of years ago, there were lizard-like dinosaurs---some the size of modern cars---that had heavy spines around the sides of their bodies; the spines probably were for defense from biting predators. Similarly, the larvae of tortoise beetles have similar peripheral spines, only they are fleshy. They may also be protective, but perhaps also help in obscuring the edges of the larva’s body if it’s threatened. These larvae can clench the substrate with their claws and pull down on their legs and body. Maybe that makes them harder for a predator to see them or pry them off for a meal? As it is, they each have that ‘anal peduncle’---a ‘tail’ that can be flexed up and down over the body. The end of it is covered with some of their feces as well as cast skins from earlier molts; it’s like an umbrella that might be waved at an attacker---or nosy entomologist. It may also help obscure the larva when it’s feeding on a leaf---even the underside of a leaf.So, marvel at these creatures---adults as well as larvae.Another thing that’s confusing about these creatures is their reported host range. Convolvulaceae is often cited. That would include field bindweed, morning glories---and sweet potatoes. Yet, in NM, tortoise beetles can be found on plants in other, very different families---like some garden vegetables as well as field-side or road-side broadleaf weeds. Series of little holes in foliage may draw your attention to affected plants---and it sure looks like adults and larvae are making those holes. I’ll believe they are doing that, but not to the extent of causing serious crop (or garden) damage."
"Eggplant Tortoise Beetle larva -
Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page (@NMDesertBlooms)
Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center.
