common name: fall webworm
scientific name: Hyphantria cunea (Drury) (Insecta: Lepidoptera: Arctiidae: Arctiinae)

Introduction - Synonymy - Distribution - Description and Life Cycle - Hosts - Economic Importance - Management - Selected References

Introduction

The fall webworm, Hyphantria cunea (Drury), is a pest of a number of ornamental trees and shrubs as well as of several agricultural crops. The larvae feed in huge nests and are able to completely defoliate trees and shrubs. Native to North America, this species has beocme an invasive pest throughout Europe and Asia, and therefore is well studied.

adult male

Synonymy

Hyphantria
liturata (Goeze, 1781)
punctatissima (Smith, 1797)
budea (Hübner, 1823)
textor (Harris, 1828)
mutans (Walker, 1856)
punctata (Fitch, 1857)
pallida (Packard, 1864)
candida (Walker, 1865)
suffusa (Strecker, 1900)

Distribution

The fall webworm originally occurred throughout North America to its northernmost limit in southern Canada. The nothern range limit for Hyphantria cunea occurs at the latitude of 50–55° (Morris 1963).

The fall webworm was introduced into Yugoslavia in the 1940s, and since then has invaded most of Europe. It now also inhabits parts of China and North Korea, again due to accidental introduction, and it is found in Japan.


Worldwide distribution as of 2010.

Description and Life Cycle

The adult fall webworm moth is bright white, with a hairy body. In the southern part of its range, the moth is white with dark wing spots while in the northern part of its range it is nearly always pure white (MPG 2010) and was once thought to be a separate species from the southern populations. The gregarious larvae form large tents around the host plant. Currently, the taxonomic status of Hyphantria cunea as a single species remains intact. The variations in phenotypes of both adults and larvae (presence of dark markings on the wings in some populations and presence of populations with red-headed vs. dark-headed larvae) has caused speculation that more than one species might be involved. For example, in Japan, DNA barcoding studies have shown that two species might be occurring there sympatrically (Takeda 2005).

adult male - northern range

adult male - southern range - dorsal view

adult male - southern range - lateral view

Like most moths, the fall webworm moths are nocturnal and are attracted to light. Adult moths have a wingspan of between 1.4–1.7 inches (35–42 mm). The bases of the front legs are orange or bright yellow.

The number of generations per year depends greatly on latitude. Southern populations may complete four generations in one year, while in the north the fall webworm completes only one life cycle. The univoltine chiefly black-headed and dark-bodied larvae tend to occurs above 40° latitude, while the multivoltine cycles with green-bodied, red or black-headed larvae tend to be found in the southern part of the distribution area.

Adults emerge as early as March in the south, but do not fly until late spring or early summer in northern areas. Mostly, the adults appear from May to August and deposit their eggs.

mating pair

Eggs: The egg mass of Hyphantria cunea is almost iridescent green in color. The egg batch contains 400-1000 eggs. The eggs are usually deposited on the undersides of leaves in the spring, in a single (black-headed larva race) or double (red-headed larvae race) layer of several hundred eggs. The egg mass is lightly covered with scales from the female's abdomen.

adult female with eggs

eggs and neonate larvae

Larvae: In one to two weeks, the larvae hatch and immediately begin spinning their silk tent. The neonate caterpillars place the web over single leaves and feed by skeletonizing.

second instar larvae

second instar larva - close-up

second instar larvae feeding

second instar larvae before molting

Mature larvae are hairy and either have a lime green body with black spots or can have darker color, especially in the later instars. The head capsules in some populations can be either red or black. In other populations, they are entirely black. The black-headed larvae are thought to be more prevalent in the northern climes, while the red-headed larvae are thought to be dominant in the southern climes. Some behavioral differences have been noted between different larval morphs. For instance, larvae of the red-headed morph stay inside the tent throughout the larval stage, while the black-headed morph leaves the tent in its fifth instar.

red-headed morph - late instar larvae

black-headed morph - late instar larvae

third instar larvae

third instar larvae feeding

fourth and fifth instar larvae

fifth instar larvae

fifth instar larvae

newly molted fifth instar larvae

fifth instar larva - dorsal view

fifth instar larva - lateral view

Pupae: Full-grown larvae leave the web to pupate in leaf litter or bark crevices. Fall webworms overwinter in the pupal stage. Pupation occurs in thin cocoons. The pupae are brown.

fifth instar larva in cocoon

cocoon

cocoon

Hosts

Part of Hyphanea cunea's success as a species can be attributed to the fact that its larvae are consummate generalists, capable of developing on a wide range of host plants. Preferred host plants include hickory, pecan, walnut, elm, alder, willow, mulberry, oak, sweetgum, and poplar.

Host plants recorded in Florida (Heppner 2007, and personal observation)

Economic Importance

In the wild, within its native range, fall webworm does not usually damage the trees, since the defoliation occurs just before leaf drop. However, Hyphanea cunea is known to cause damage to ornamental trees, and is also known as a pest of sericulture because of its preference for mulberry leaves (Franz 1961, Yang & Zhang 2007).

damage to trees

leaf damage

A fall webworm tent normally encloses the foliage at the end of a branch. The caterpillars can build large silk tents that sometimes spread over several branches. At maturity, the larvae may reach one inch in length. Throughout their development, the caterpillars are able to make distinct jerking movements in unison if the nest is disturbed.

tent over foliage

numerous tents

Management

Biological control. Parasitoids attacking Hyphantria cunea include:

parasitoid

parasitoid

parasitoid

Chemical control.

Florida Insect Management Guide for commercial foliage and woody ornamentals
Florida Insect Management Guide for pecans

Selected References

Authors: Andrei Sourakov and Thomson Paris, University of Florida
Photographs: Andrei Sourakov, Lyle J. Buss, Thomson Paris and James Castner, University of Florida
Project Coordinator: Thomas R. Fasulo, University of Florida
Publication Number: EENY-486
Publication Date: December 2010. Latest revision: April 2011.
Copyright 2011 University of Florida

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