Ornamental trees suffer from insect pests as other trees do. Trees grown for their good looks and shade, such as the northern catalpa, must deal with pests like the Comstock mealybug. Others, like the flowering dogwood, are often at the mercy of the dogwood borer, a type of moth that lays its eggs on the tree, with serious consequences for the dogwood. The Japanese beetle is an equal opportunity diner, selecting many trees as its food source, but the American basswood is among its favorites.
The northern catalpa has large leaves, showy flowers and produces a hanging pod of seeds that make it an unusual but very desirable ornamental species. One of the biggest insect threats faced by a catalpa is the Comstock mealybug, which has a long oval body that has a flat appearance. Very short spines stick out along the edges of this mealybug, with two longer ones in the rear that make it look as if the insect possesses a tail. The males have wings, while the females do not. This type of mealybug will lay its eggs in the crevices that exist in a catalpa's bark, where they survive the winter before hatching in the spring, conveniently right after the leaves of the tree emerge. The young mealybugs go to town eating the leaves, and a serious infestation is capable of damaging the health of the tree. These bugs will also feed on mulberry trees as well as poplars, holly, fruit trees and boxwood, according to the Ontario Ministry of Natural Resources website.
The dogwood borer is a moth that lives for about a week once it completes its transformation from larval stage to adult. As an adult moth, it resembles a wasp in appearance, but this phase of the pest is not the one that damages a tree. The adult female dogwood borer seeks a tree such as an apple tree or a flowering dogwood on which to lay its eggs, looking for a knot on the tree to deposit them. These eggs hatch in about eight days, and the larvae seek to get into the knot and bark by any opening, such as a wound from a broken branch. Once inside they feast on the inner bark and wood. The larvae then spend the winter in a hibernation chamber they chew into the bark, finally emerging as adults in June or July after a pupal stage of around 25 days. Over several years, continued infestations of the dogwood borer can kill the tree. Ornamental trees like the flowering dogwood and many kinds of oaks are the frequent victims of this insect pest.
Ornamental trees are not the sole target of the Japanese beetle, an insect pest first detected within the borders of the United States in 1916. The grubs feed on plant roots and then emerge after as long as 10 months under the ground as an adult with a metallic green body and bronze-colored wings. These adults will then move onto the foliage of hundreds of different kinds of plants. American basswood is a popular ornamental tree that Japanese beetles will gladly eat the leaves from. They not only chew up the leaves, defoliating entire portions of the upper tree, but they exude a chemical "welcome mat" that leads other Japanese beetles to the scene, increasing the amount of damage.