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Joseph F. Boggs, Ohio State University Extension, Hamilton County/Southwest District; Curtis E. Young, David J. Shetlar, James A. Chatfield, Erik A. Draper, Pamela J. Bennett, Gary Y. Gao, |
Other Caterpillars
Localized outbreaks of fall cankerworms (Alsophilia pometaria) and spring cankerworms (Paleacrita vernata) were observed in southern Ohio. Despite their common names, which indicate the seasons when the flightless female moths lay their eggs, both of these species of loopers, or inchworms, appear as larvae in the spring. They consume all of the leaf except the midvein and will feed on a number of deciduous trees including oak, linden, elm, apple, and beech. Both species have a single generation per year.
Aside from being general defoliators, the caterpillars are also capable of becoming a significant nuisance pest. Caterpillars are able to spin down from trees on silk threads. This behavior is usually only expressed when the caterpillars are about to pupate. However, during high population outbreaks, the caterpillars may vacate trees throughout their larval development in search of food. Large numbers of caterpillars descending on silk threads onto cars, pets, people, etc., is a disconcerting experience for affected homeowners. Such an event was observed in the Cincinnati area this past season.
In the spring, common armyworm (Pseudaletia unipuncta) caterpillars grabbed the attention of farmers in western Ohio with large populations devouring wheat fields and marching into corn fields to feed on those plants as well. The armyworm caterpillar is primarily a grass-feeding insect. While there were isolated reports of damage to turfgrass, the primary problem created by the large number of caterpillars was the correspondingly large moth (adult) populations that occurred in late June.
BYGLers throughout western Ohio reported numerous phone calls regarding large numbers of armyworm moths clustering in and around linden trees. The linden trees were in full bloom and producing large quantities of nectar which attracted the moths. Callers reported that the trees almost seemed to pulse with the moths flying in and out of the trees. Fearing their linden trees were under attack, many asked for control recommendations. Fortunately, the armyworm moths were causing no harm to the trees because they are nectar feeders. Insecticide applications were not only not justified, they would have done more harm than good. Several other species of insects are also highly attracted to the blooming linden trees, including other moths, butterflies, and honeybees. These insects would also have been killed by an insecticide treatment.
Two general defoliators in the genus Datana were observed in central and southern Ohio in early August. Walnut caterpillars (D. integerrima) feed on their namesake as well as hickory and oak. Yellownecked caterpillars (D. ministra) possess a more cosmopolitan palate, feasting upon walnut, hickory, and oak, as well as crabapple, cherry, maple, elm, beech, linden, birch, black locust, azalea, sumac, and boxwood. Pockets of heavy defoliation from both species were observed, but yellownecked caterpillars were more commonly found and seemed to be more widespread. Populations of this caterpillar have been on the rise over the past seasons (6, 7, 8).
Heavy infestations of late instar ailanthus webworms (Atteva punctella) on tree of heaven (Ailanthus altissima) were observed at two locations in southwestern Ohio in late September. The webworms are capable of defoliating their odoriferous namesake and may feed on stem tissue once all leaves are devoured. For example, tree of heaven seedlings/suckers and saplings were found to be seriously damaged, if not killed, by caterpillars gnawing away the tender bark. Such an observation would normally cause concern if damage occurred on a preferred tree species, but since the damage occurred on a nonnative, invasive tree, the webworms were applauded for their biocontrol efforts! Small populations of this insect were also observed in southwestern Ohio during the 1998 season (6).
Larvae of this ermine moth produce nests by pulling several leaflets into a network of loose webbing. They then live within the nests, consuming the leaflets bound by the webbing. The webworm caterpillars can grow up to 1" to 1-1/2" long, and they have a wide, light greenish-brown stripe down their backs and several thin, alternating white and olive green stripes along their sides. They are sparsely covered with short, erect hairs, which help to suspend the caterpillars within the webbing. When disturbed, the caterpillars move backwards out of the nest and drop towards the ground on strands of silk.