Common Insects Found in Central Illinois


Bagworms (see left) are a common problem among the evergreen trees, particularly arborvitae and spruce trees. The larvae emerge in the spring after overwintering in bags that can contain between 300-1000 eggs. The larvae feed on the foliage of the host plant and can cause serious damage if left unchecked. Repeated infestations can cause total defoliation and result in death of the host plant.


Borers are a major problem to most tree species. Borers tend to be an opportunistic pest and attack stressed trees that are in decline. During the larvae stage, borers tunnel around under the bark in the phloem and cambium tissues. Damage to these tissues impedes or restricts the flow of water and nutrients throughout the tree, causing wilting, dieback and sometimes death to branches and twigs.

Emerald Ash Borer

Emerald Ash Borer is small metallic green beetle that has killed millions of Ash trees since its discovery in the United States in 2002. It was discovered in northern Illinois in 2006. In the summer of 2014 Emerald Ash Borer was found in Peoria and Tazewell County. After the Emerald Ash Borer lays eggs in an Ash tree during the summer months, the eggs hatch in the fall and turn into larvae which tunnel around the cambium layer during the winter months. As a result of the destruction of the cambium layer, the tree can no longer transport the necessary water and nutrients throughout the tree, thus causing tree decline and eventual death.

Japanese Beetles

  Japanese Beetles are oval bronze and metallic green beetles that feed on hundreds of different types of species of plants with certain trees being more preferred over others. Lindens, Ornamental Plums, Crabapples, Elms, Birch, Norway Maples and Swamp White Oaks are some of the trees more commonly attacked during the summer months by the Japanese Beetle.

Magnolia Scale

  Magnolia Scale can affect all types of magnolias but the star and saucer magnolia are the most commonly affected. Scale have sucking mouthparts that extract fluid from the stems and branches. A high population can cause dieback of branches and stems, while a severe outbreak of scale can cause tree death.

Pine Engraver

  Pine Engraver is a type of bark beetle that attacks white pines among other pines in Illinois. The beetles attack stressed and nearby healthy pines. After boring into the tree, the beetle infects the pine with the blue stain fungus, which in turn can kill the healthy trees.


Mites are a problem to a variety of trees, both deciduous and conifers. Some mite infestations, such as the eriophyd mite, will cause the creation of galls to form on the leaves while other mites will cause needle or leaf damage such and leaf blistering or stippling

Pine Needle Scale

  Pine Needle Scale is an insect that attacks not only pines but other conifers as well. The insects suck the juices from the needle. Heavy infestations can kill branches or entire trees.

Pitch Borer

Pitch Borer is a common issue in older pines. During the larvae stage, the borer tunnels under the bark and damages tissues, weakening the trunk and branches. Branches may die and the trunk can snap off where repeat tunneling has occurred. Whitish, crusty, popcorn like “pitch” can be seen where larvae have entered the tree. Tree death can occur from repeat infestations.