A recent find from a homeowner in New Smyrna Beach (Volusia County) has us scratching our heads. A resident was pruning his pink Powderpuff tree (Calliandra haematocephala), when it led him to the discovery of Thorn bugs, Umbonia crassicornis (Amyot and Serville). Thorn bugs are found in south Florida but it is rare they have traveled this far north to Volusia county. Nonetheless, in heavy infestations, they are a remarkable sight.
Thorn bugs are found in tropical South America to Mexico and Southern Florida and gets its name from its tall, essentially perpendicular thorn-like dorsal horn. This structure discourages birds and other predators from eating it, if only by mistakenly confusing it with a thorn.
Damage & Hosts
Unfortunately, heavy infestations will cause damage to your powderpuff tree by piercing the plant tissue and sucking the sap and making cuts in the plant in order to lay their eggs. Some plants experience considerable loss of foliage, and general and extensive terminal twig death. Some additional hosts other than powderpuff (Calliandra spp.), that have experienced damage to these pests includes Hibiscus sp., Acacia spp., Jacaranda (Jacaranda acutifolia) and Royal Poinciana (Delonix regia). Honeydew secretions from the insect and accompanying sooty mold development is a nuisance to homeowners.
Four species of Umbonia are present in the U.S., but they chiefly found in the subtropical regions. The most common is Umbonia crassicornis. The thorn bug varies in size, color and structure, particularly the pronotal (dorsal) horn of males. Typically, the adult is about 0.5 inch in length and is green or yellow with reddish lines and brownish markings (Mead 2000).
Biology and Communication
Females lay their eggs in the tender bark of twigs and the eggs hatch about 20 days later. The female actively tends her clutch, which can number from 15 to 100 nymphs. Developing nymphs have three horns instead of the one seen on the adults. While four generations occur per year, females lay only a single clutch of eggs. (Johnson and Lyon 1994). The species has a chemically triggered vibration in communication that aids in the defense of the young. This chemical passes between the parent and nymphs, making them distasteful to potential predators (Johnson and Lyon 1994).
All stages of the insect can be found throughout the year. The shocking heavy infestations have occurred in all seasons but primarily in cooler months (Mead 2014).
There are neither biological treatments nor specific chemical products recommended for this pest. I’d recommend using horticultural soaps and oils or for heavy infestations, the use of Sevin SL-Carbaryl insecticide. Always read the label for directions on product use rates. For more information, contact your local UF IFAS Extension office.
Johnson WT, Lyon HH. 1994. Insects that feed on trees and shrubs. Cornell University Press. pp. 1–560.
Mead, F. W. 2000. Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville, FL. UF EDIS publication. This document is EENY175, one of a series of the Entomology and Nematology Department, UF/IFAS Extension. Original publication date November 2000. Revised August 2014. Reviewed December 2017. open Link below