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Mimosa Webworm

Homadaula anisocentra Meyrick

The mimosa webworm feeds primarily on the leaves of mimosa and honeylocust trees. It was unintentionally introduced from China into the United States during early 1940s. This pest was first reported in Washington, D.C. During this same period improved (thornless) varieties of honeylocust, Gleditsia triacanthos, were planted as replacements for American elms killed by Dutch elm disease in these landscapes. This decision may have led to the spread of mimosa webworm and possibly other key pests of honeylocust.

DESCRIPTION


At maturity larvae are about 16 mm long, grayish to dark brown and have five white stripes running the length of the body. The head is brown and the body is slender. They are very active and, if disturbed, will wriggle and lower themselves on silk strands. The 6 mm long yellowish brown pupae are found within whitish silken cocoons.

It is rare to see an adult. They are steel-gray moths with small black dots on their forewings. Adults have a 13 mm wingspan. The eggs are very small, oval, and white that turn a rose color just before hatching.

LIFE HISTORY

There are two generations of this pest each year in Pennsylvania. First generation adults appear in early to mid-June, and they may live for several weeks. Females lay eggs on the terminal leaves and small twigs as well as on webs from the previous year. Larvae hatch in mid- to late June and immediately begin to feed on the lower surface of leaflets. Mature larvae from the first generation pupate in mid-July and the second generation of adults appear from late July through mid-August. Second generation larvae are active during August and early September. Larvae from this generation may be so abundant that they web leaves throughout the entire crown of the tree causing it to look completely brown. Pupae from this second generation overwinter inside cocoons within the web or in to bark crevices, house siding, mortar joints, or other protected areas.

DAMAGE

The larval stage of this pest is the most damaging life stage. As larvae feed, they spin a web around leaflets and continue to feed within this protected area. The foliage appears skeletonized, turns brown, and then may die. If left alone, an infestation may progress and completely defoliate a tree by early September. Often an entire plant may be webbed by September. Mature larvae are sometimes a nuisance as they silk down and get into homes and other dwellings.

MANAGEMENT

The most effective management is prevention. Thornless cultivars of honeylocust are very susceptible to attack by this pest. G. triacanthos 'Sunburst' is especially vulnerable, while, 'Moraine', 'Shademaster', and 'Imperial' are less susceptible. Extensive plantings of susceptible honeylocust may result in the need for chemical management of this pest. Keeping leaf debris and webbed foliage cleaned up from beneath and around host trees may reduce the chances of an infestation.

Registered formulations of insecticides are effective when applied just after the egg hatch when larvae are small and have just started to feed. First generation larvae should be managed during mid- to late June and the second generation require treatment in August.

Authored by: Barbara Knupp, Graduate Student - Horticulture

Gregory A. Hoover, Sr. Extension Associate

Revised July 2012

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