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 Variable Oakleaf Caterpillar

Variable Oakleaf Caterpillar

We have had many calls recently about the worms eating the oak tree leaves and leaving their nasty “debris” behind.  Many residents are battling the shredded leaves and brown droppings on a daily basis.  This nuisance is causing problems in swimming pools, pet water and feed bowls and on many decks and patios.  So what is this worm and how do you fix the problem??

The Variable Oakleaf Caterpillar (Lochmaeus (Heterocampa) manteo) is a native species that occurs in deciduous forests throughout much of eastern North America. Although outbreaks have not been uncommon throughout much of its range, it has been several years since I can remember an outbreak of this magnitude in Arkansas.

Hosts

Larvae of this insect feed on the foliage of a large number of deciduous trees. All species of oaks are attacked; however, white oak is generally preferred. Infestations are commonly recorded on southern red, northern red, pin, willow, black, laurel, bur, and post oaks. Exotic oaks, beech, basswood, paper birch, and American elm also are attacked. Occasional hosts are walnut, black birch, hawthorn, eastern hop hornbeam, apple, box elder, and persimmon

Injury

Trees of all sizes are attacked by this insect. The greatest amount of feeding usually occurs in August or later; consequently, saplings or larger trees can withstand 2 or 3 consecutive years of extreme defoliation before mortality occurs. Infestations seldom last longer than 2 years, during which time tree vigor and growth are impaired. In severe outbreaks an occasional tree may be killed, but the major effect is unsightly defoliation that degrades forest recreation sites.

Description and Life Cycle

The tiny spotted larvae of the variable oakleaf caterpillar at first feed gregariously on the lower leaf surface near the expended egg shells. They usually skeletonize portions of one to three leaves in a cluster. They also separate after the first molt and begin to feed singly. From this point on they cease to skeletonize and consume entire portions of the leaf. They pass through five instars prior to dropping to the soil to pupate. At maturity the color is generally green but a fairly high percentage of individuals may be deep pink or reddish. Mature larvae are roughly 1.5" long with a distinctive dorsal band which is often dark red in color. The head is most often green with two darker vertical lines which are usually black, edged with creamy white. There is also a definite yellowish lateral line along each side of the larva at or below the spiracles (breathing pores) which separates this species from other prominents (Heterocampa).

Mature larvae drop to the soil when done feeding, usually in late August or September. They burrow into the soil beneath the leaf litter and form a loose silk lined cell. Here they become inactive larvae (pre-pupae) and remain in this state throughout the winter.

Pupation of this species usually takes place in the soil cell in late May or June of the next year. Some individuals, however, remain prepupae throughout the entire following season and pupate in May or June of the second spring following defoliation. Pupae of the variable oakleaf caterpillar are about .75" long, light chestnut brown, smooth and shiny.

One generation per year is normal in the northern areas of the variable oakleaf caterpillar's range. In areas south of a line extending from Virginia to Missouri, two generations have been reported. However, only one generation usually reaches outbreak population levels in any one place each year.

The insects over winter as pre-pupae in cocoons under the leaf litter. Pupation usually occurs the following spring; in heavy outbreaks, however, over 50 percent of the insects may remain as pre-pupae for a second year or longer.

In the North, the moths begin to emerge near the end of June and continue to emerge through late July. Females lay their eggs in clusters of 30 to 300 on the lower surface of host leaves. Each female may lay as many as 500 eggs, which hatch in 5 to 7 days.

At first the young larvae feed gregariously, skeletonizing the lower surface of the leaves. As they become older, they consume all the foliage between the major veins. Larvae in the last stage account for about 85 percent of the defoliation.

When disturbed, larvae defend themselves by secreting formic acid from a gland on their ventral thorax. Prolonged or repeated handling of the larvae may cause blisters. Larvae cease feeding early in September, drop to the ground, crawl into the duff, and spin their cocoons.

In the South, some moths may begin to emerge about mid-April or early May. Eggs are usually present by the end of April. Larvae hatch from these eggs in May, feed until late June or early July, and then pupate in cocoons in the leaf litter. Adult moths appear and lay eggs by late July. Second-generation larvae begin feeding by mid-August, paralleling the development of northern populations. Upon completion of feeding in September, they move to the ground and spin their cocoons. This generation over winters as pre-pupae and pupates in April of the following year.

Development varies from year to year, depending on local weather conditions or latitude. In one instance in Arkansas, larvae were observed feeding in January.

Associated Insects

Variable oakleaf caterpillars are frequently found feeding with one or more other species of related Lepidoptera. Such combined feeding activity defoliates a stand of trees more severely than feeding by the oakleaf caterpillars alone. The most commonly associated species are the redhumped oakworm (Symmerista canicosta Fran.), the yellownecked caterpillar (Datana ministra (Drury)), the walnut caterpillar (Datana integerrima G. & R.), the saddled prominent (Heterocampa guttivitta (Wlkr.)), and the orangestriped oakworm (Anisota senatoria (J. E. Smith)). All these caterpillars belong to the variable oakleaf caterpillar family or are close relatives and have similar life histories and habits.

Natural Control

In years following large infestations, the egg parasites Trichogramma sp. and Telenomus sp. may kill 90 percent of the eggs. Nearly all egg masses have some parasitized eggs; only the eggs concealed within a cluster escape. This high level of parasitization, plus the failure of many prepupae to pupate in the spring, appears to be the major reasons for lack of consecutive heavy defoliations.

At least seven species of larval parasites attack variable oakleaf caterpillar larvae. The most important species are Diradops bethunei Cress (Ichneumonidae), Protomicroplitus schizurae (Braconidae), and Lespesia schizurae (Tachinidae). Combined larval parasitization may kill 90 percent of the larvae.

The large predatory ground beetles Calosoma scrutator (F.) and C. calidum (F.) feed on the variable oakleaf caterpillar. Adult checkered beetles and stink bugs often prey on small larvae. Most birds do not prey upon active larvae although prepupae have been found in the crops of ruffed grouse and wild turkeys.

Direct Control

Most outbreaks, although spectacular, subside before tree mortality occurs. Chemical control is generally neither necessary nor recommended over large areas. However, localized treatments using pesticides may be necessary in residential or recreation areas. Since most of the calls I have received are large and this outbreak is widespread, control is most likely impractical.  It looks like we will have to tolerate this nuisance and keep the broom and pressure washer handy to clean up their manure and the shredded leaves. 

 

Control*

Normally populations of these late season defoliators drop out after two or three years in any one area without serious impact. Chemical control is neither necessary nor recommended in forest stands and the most significant damage occurs where a stand is opened up due to heavy defoliation. In this case heat and/or drought can cause serious root damage resulting in dieback or mortality of severely stressed trees.

*NOTE:These recommendations are not a substitute for pesticide labeling. Read the label before applying any pesticide. Pesticide recommendations are contingent on continued EPA and Maine Board of Pesticides Control registration and are subject to change.

Caution: For your own protection and that of the environment, apply the pesticide only in strict accordance with label directions and precautions.

By Sherri Sanders
County Extension Agent - Agriculture
The Cooperative Extension Service
U of A System Division of Agriculture

Media Contact: Sherri Sanders
County Extension Agent - Agriculture
U of A Division of Agriculture
Cooperative Extension Service
411 No Spruce Searcy AR 72143
(501) 268-5394
ssanders@uaex.edu

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