A little caterpillar can defoliate “black olive” and its finer textured variety “ ‘Shady Lady’ black olive” (Bucida buceras). Nuisance calls — complaints about the caterpillars, not the calls — usually start in mid to late April.
People start fussing about the caterpillars rappelling around and dropping out of the canopy and getting in their faces. Because of this behavior, some landscapers have nicknamed them the “bungee caterpillars,” but their scientific name is Characoma nilotica.
After flowers of infested trees have been consumed, the caterpillars move to the upper canopies causing them to turn brown and defoliate. (Because these “black olive” trees are not in the olive family, I will refer to them as bucida or bucida trees.) Back in 2002, the bucida canopies were 50 percent to 100 percent browned and defoliated. This much leaf loss early in the growing season, in early May, is major stress, if not sure death, for some tree species.
Certain streets of Naples reminded me of October leaf drop in Ohio, with all of the leaf litter. But the bucida trees quickly refoliated within four to six weeks without any negative long-term effects. The caterpillars are reported to also feed on buttonwood (Conocarpus erectus), but I’ve never observed it.
Oddly, these caterpillars are more into vandalizing the trees rather than consuming them for food. Young larvae initially feed on the delicate flower clusters. They float around on silken threads even when there is no wind, perhaps looking for more flowers to feed on in the lower canopy. Later, larger larvae will chew some foliage, lightly skeletonizing the lower leaf surface.
The brown and defoliating leaves are not actually consumed, but rather the petioles are clipped and the leaves are used to create a feeding niche or a place to hide and spin up their little white cocoons. Cocoons are also found in the fruit clusters. The dull gray moths emerge from the cocoons in about three weeks.
Not much information is available on the behavior of this moth. Some years, eggs of a second generation are deposited on 4- to 12-inch-long, string bean-like galls, which develop from the bucida flowers. The larvae then tunnel into the galls and feed inside. These galls are caused by a tiny mite, Eriophyes buceras, which feeds on the developing flower bud. The mites flourish and millions can be found inside the gall when it is cut open. This gall can be straight or curled and was the reason for one of the earlier common names, ox-horn bucida.
The severe, rusty staining is due primarily to the frass of the caterpillar. The bucida leaves have tannins, much like oak and tea leaves, which may cause a lighter stain. But apparently the tannins are concentrated in the caterpillar frass droppings (waste) and the staining is much more severe.
It isn’t the fruit or the leaves that cause the objectionable staining, it is the caterpillar frass. So some years, when the populations dwindle, you will not have much staining. But when the caterpillar population is in the upswing you will have staining, which will eventually bleach out in the sunlight or weather away after a few months.
Unless the tree has been struggling from poor soil or lack of water, caterpillar management attempts seem to be unwarranted. However, keep a close eye on these defoliated trees as borers reportedly may attack when trees are in a weakened condition, but I haven’t seen this happen in the last 10 years.
If you wish to alleviate the dangling caterpillar annoyance and the staining beneath the tree, applications of pesticides would have to be applied while the caterpillars are small, probably when the trees first start to flower, say, sometime in the first two weeks of April. If they are caught early, the staining damage could be minimized.
However these little caterpillars are usually not noticed until the damage has been done and it is too late to spray. A product with B.t. or spinosad as the active ingredients would be the “soft” pesticide product of choice. If the larvae are larger, Talstar (bifinthrin) will provide quick knock-down. I have not observed bees attracted to the flowers, so there would be no impact to the bee populations.
See more on the bucida trees (three fact sheets) at our web site: collier.ifas.ufl.edu
Doug Caldwell, Ph.D., is a commercial landscape horticulture extension educator with the University of Florida Collier County Extension. Email: firstname.lastname@example.org ; call (239) 353-4244 ext. 203.