As far as insects go, the Edwards wasp moth is a colorful sort with purplish-gray wings, a shimmery blue body and orange head.
The moth, a member of the Lepidoptera order, which also includes butterflies, is a well-known pollinator of orchids.
But people on Sanibel who grow or have a strangler figs and other Ficus-related plants don't care that the moth is an eye-catching member of the Arctiidae family. The residents' main issue, and it's a big one, is that during one part of the life cycle of the insect — its caterpillar stage — it has a particularly voracious appetite for all things Ficus.
Recently, Sanibel residents have been reporting a rapid defoliation of their strangler fig trees — Ficus aurea, if you will — which have otherwise shown great resilience after Hurricane Ian.
Dr. Joyce Fassbender, an anthropologist and expert in insect and spider biodiversity in the biology department at FGCU, said the Edwards wasp moth caterpillar is the culprit here.
"Well, it's not uncommon to have the Edwards wasp moth on Ficus trees, that is their primary food source," Fassbender said. "It's not uncommon to have a lot of them on Ficus trees this time of year because this is when you have mating and babies coming out. And that's when you get the caterpillars."
Fassbender said Hurricane Ian is in large part what is probably causing this massive explosion of the Edwards wasp moth caterpillar.
"With Ian there was a lot of damage to a lot of the non-native Ficus. So you get this spread to other other Ficus trees." she said. "The biggest issue is that in normal years, we don't see this number of Edwards wasp moths because they are very well controlled by their native predators: flies, stinkbugs and wasps. To the point where over two-thirds to three quarters of the caterpillars get parasitized or eaten by other insects. The problem is that when you have a giant storm come through and wipes out a large number of the insects, the ones that feed on plants are the ones that are gonna rebound first."
After that, she said, you start to get the predators and the ones that parasitized the ones that feed on plants.
"We're waiting for those predator numbers to increase in order to decrease the number of caterpillars," she said, adding that the numbers of the predators and parasitoids, "will slowly increase over time and you should start to see a decrease (in caterpillars) within the next couple of months."
The insect species is native to Florida and commonly found in the southern region of the state. Due to their annual breeding cycle, the pale yellow to cream colored caterpillars may be found at any time of the year.
Fassbender also said that this Edwards wasp moth caterpillar infestation is not a first in Florida after a hurricane.
"After Irma, they saw a very similar phenomenon take place in the Keys," she said. "They had a large explosion of the Edwards Wasp moth caterpillar feeding on the Ficus. And their Ficus recovered just fine."
Fassbender also had one caveat for those thinking of blasting the caterpillar with pesticides in retaliation.
"It is strongly not recommended that you use pesticides to kill them because these trees are very large. And if you spray pesticides over the tree, that pesticide will go to the entire area," she said. "The moth itself is actually a pollinator. It's actually one of the most important pollinators of orchids. So, if you kill off all of those moths, you lose a pollinator. By having all of that pesticide in the environment, you also kill off all the other pollinators, the bees, the butterflies. So, you don't really want to use pesticides to control them. Nature will take care of themselves. Nature will take care of it on its own."
There is a bacteria control for the caterpillar called Bacillus thuringiensis or BT. But Fassbender had a similar caution to make about its use.
"It's actually a spore of bacteria that can be used potentially to control small infestations on small plants. But you don't want to use that for the big plants because that can still be damaging to the rest of the insects in the population," she said.
The moth's life cycle and other facts
Information below, from the University of Florida Entomology and Nematology Department, shows that the caterpillars of Edwards wasp moth frequently usually cause extensive injury to trees in the Ficus family, and other aspects of the insect.
- Edwards wasp moth is common throughout southern Florida. It has been reared from as far north as Monticello (Jefferson County), but most records are from south of a line from St. Petersburg to Vero Beach (Kimball 1965). There are continuous generations in southern Florida, and caterpillars may be found any month of the year. Distribution records may not be entirely indicative of the true range. Once larvae mature, they crawl about and pupate on walls of buildings as well as on many non-hosts. Therefore, movement of nursery plants with attached pupae may result in its presence in areas well outside its normal range.
- The adult's size varies, but the wingspan usually ranges from 35 to 40 mm. The wings and thorax are bluish gray. The abdomen is blue dorsally and white ventrally. The prothorax and head are orange-yellow ventrally. Dorsally and laterally the posterior portion of the head and anterior margin of the prothorax are orange-yellow. The antennae are pectinate, meaning it has narrow projections or divisions set closely in a row.
- As far as known, the caterpillars feed only on Ficus spp., and the following host species have been recorded: Ficus altissima Blume, Ficus aurea Nutt., Ficus auriculata Lour., Ficus benghalensis L., Ficus benjamina L., Ficus continifolia HBK, Ficus elastica Roxb. ex Hornem, Ficus lyrata Warb., Ficus retusa L. and Ficus rubiginosa Desf. ex Venten.
- More than a dozen other plant species have been recorded as larval hosts, but these reports apparently represent mature larvae looking for pupation sites as well as those which have become dislodged from their host plant and are searching for food.
- The caterpillars can be quite destructive to Ficus trees. They may feed on leaf margins or chew irregularly shaped holes in the leaves. Their habit of spinning cocoons on the walls of houses can be a nuisance to homeowners. There have been reports of up to 35 pupae, prepupae, and abandoned cocoons and pupal cases per square foot on some buildings.
- Check damaged Ficus leaves for fuzzy, whitish yellow caterpillars with a conspicuous white triangle on the front of the head. The brown pupae are in a flimsy cocoon attached to leaves, trunks, or walls of buildings near Ficus trees.
- Parasitization of caterpillars and/or pupae is very heavy especially in late summer and fall. Bratley (1929) reported 96 % parasitization by the tachinid fly, Phorocera claripennis Macquart (now in Euphorocera), and the chalcid wasp, Brachymeria robusta (Cresson). Genung (1959) reared two chalcid wasps, Brachymeria robusta (Cresson) and Brachymeria ovata (Say) and a tachinid fly, Lespesia aletiae (Riley) from pupae and a scelionid, Telenomus sp., from the eggs. Up to 89.5% of larvae and pupae and 40% of eggs were parasitized in July. Genung also found three species of pentatomids (stink bugs), Podisus maculiventris (Say), Podisus mucronatus Uhler, and Euthyrhynchus floridanus (L.), preying on the caterpillars.
- Edwards wasp moth caterpillars may be controlled with Bacillus thuringiensis which is available in several formulations from several companies. Instructions on the package should be followed. This insecticide will provide control without leaving chemical residues or harmful effects on parasites and predators.
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