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Umbonia crassicornis Amyot & Serville, a continental tropical American treehopper or membracid, probably was introduced accidentally into Puerto Rico from the mainland. The manner of introduction is not known, but possibly either with infested plant material hidden in passenger baggage or as a fertile female hitchhiker in an airplane arriving at San Juan from the U.S. where it apparently found suitable breeding conditions in the vicinity of the Isla Verde International Airport. This treehopper mainly attacks leguminous trees. It was seen first in the Santurce area of San Juan, in May 1972, attacking its favorite host, Pithecellobium dulce trees. It since has spread throughout several towns in the interior of the Island, and along the north and west coast as far as Mayagüez. It has been recorded locally thus far on 11 different host trees. Umbonia is considered to be a pest of ornamental trees and thus is of economic importance. Although it has not killed trees thus far in Puerto Rico, it has affected their appearance by destroying many of their twigs and branches. When massive infestations occur, adults of both sexes and their nymphal stages are present by the thousands on the branches of the trees. The insect secretes honeydew, a sugary substance favorable to the growth of sooty-molds. These fungal growths cause blackening of foliage of plants upon which the honeydew falls. The female has a long pointed spinal process on the pronotum. This horny, splinter-like protuberance is a nuisance for barefooted people, as well as for those who catch the insect inadvertently. These treehoppers can be controlled by periodic spray applications of any one of the following insecticides: Diazinon AG-500, Spectracide, Sevin 80, Malathion 57%, Isotox Garden Spray, and Endosulfan.