Mysterious mangrove moth
STRI/DICYT Earlier this month, bloggers in Bocas Del Toro drew attention to an island in Dolphin Bay near Bocatorito where red mangrove trees are drying out. “I watched this particular mangrove go from green to brown in a matter of two weeks,” wrote sailboat captain Steven Guling in a note to STRI staff scientist Andrew Altieri. “One local kid who often comes to my boat while in Dolphin Bay was describing a worm with teeth but at the time it wasn't quite that clear and I thought he was referring to something in the water.”
Altieri has studied crabs that defoliate coastal habitats. “The first question is what is causing the outbreak, and the next question is how the area will recover, which will depend on what is eating the trees and other local environmental factors,” he said.
The trees were festooned with spikey, neon-green caterpillars. Based on a couple of photographs, Ilka Feller, a mangrove expert and senior scientist at the Smithsonian Environmental Research Center in Maryland, identified the suspect as a member of the moth genus Automeris, in the same insect family as the Saturniidae.
“I believe that the caterpillar is Automeris io. I’ve found it on the mangroves at a number of locations at Bocas, but never in such large numbers,” Feller wrote. “Outbreaks like this are difficult to explain because they happen so infrequently. I'm pretty sure this guy only eats leaves. I haven't seen it eating the apical buds. So, if the apical bud is not damaged, after the caterpillars are gone, the trees will leaf out again.”
There are more than 125 species in the genus Automeris. And it is a challenge to identify plants and animals based on photos. Distinguishing different species may require counting the number of hairs on a body part or some other detail that is not visible in images.
We asked Annette Aiello, a STRI staff scientist whose specialty is the lepidopterans –the butterflies and moths–to look at the photographs to see if she could identify the species. Based on the first set, Annette said: “A. io is a good match, though a few more photographs, especially one of the head would be helpful. One has several black marks that lead me to suspect that this individual has been parasitized by wasps.”
Wasps parasitize the caterpillars, injecting their eggs into their soft bodies, where they feed and eventually kill their hosts.
We sent Annette another set of photos with close-ups of the head and better photographs of the body. “Based on photograph 3047, which shows the dotted pattern between body segments, I will change my diagnosis to either Automeris jucunda or A. tridens,” said Aiello.
“Whatever these guys are, the females [moths] lay lots of eggs and all you need is a few of them to produce an outbreak such as the one you describe, especially if, at the outset, their parasitoids are temporarily in short supply. An outbreak would not be surprising given that mangroves tend to be relatively isolated from other habitats. Mommy Nature will bring them back under control,” she said.
In the meantime, while we were trying to find out if someone had a research permit that would allow us to bring the caterpillars from Bocas Del Toro to Panama so that Annette could take a closer look, they metamorphosed. Now they are pupae covered by some cobwebby silk and attached to the bottoms of some dried-up leaves. Eventually, they will become moths with the distinctive eyespots on their wings.