These insects can be so abundant that they make a smooth twig look like it is covered with thorns. The adult thorn bug is about four-tenths of an inch long. The females have the pointy spikes on their thorax, whereas the males have a hatchet-shaped or blunt projection. These insects suck sap from the twigs, but it takes large numbers to cause any damage.
Damage also occurs when the females cut and saw into the bark with their special ovipositor kind of like a modified stinger that wasps have to deposit their egg clutches. These slits are also used by the immatures (nymphs) as easy feeding spots. This insect feeds on plants year-round because there are four generations per year.
The first indication of an active population is the accumulation of sooty mold that thrives on the "honeydew" waste excreted by the thorn bug.
Common hosts include: avocado fruit, cassias, citrus, bottle brush, jacaranda, lychee, powderpuff, sweet acacia, tamarind, wild tamarind, woman's-tongue tree (Siris tree) and small, royal poinciana trees. These have been killed by the thorn bug. It would not be a good idea to plant these tree species near a playground or an outdoor activity area where there are picnic tables, as the "thorn" on these bugs is quite stout and may pierce the skin.
What to do: Frequent applications of insecticidal soaps may work on the immature stages. If serious populations have developed a spray that contains bifenthrin or cyfluthrin or a root drench with a systemic product that contain imidacloprid may reduce thorn bug populations. (Editor's note: For gardeners who want to know more about chemicals before they use them, the following Web site may be helpful: extonet.orst.edu).
Doug Caldwell is the commercial landscape horticulture educator with the University of Florida Collier County Extension Service. For more information on home gardening, contact the Master Gardener Plant Clinic, at 353-2872. For specimen identification, the Extension Plant Clinic at 14700 Immokalee Road is open 9 a.m. to noon and 1 p.m. to 4 p.m. Monday, Wednesday and Friday; call 261-8208 to for downtown hours. Web site: collier.ifas.ufl.edu