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.
HOST:
Honeylocast:
Sunburst seems to be the most susceptible to webworm attack. Other varieties including
Shademaster, Skyline, Moraine and Imperial are less susceptible but still subject to severe injury.
Mass plantings of any of the thornless varieties should be avoided
LIFE CYCLE:
Mimosa webworm has two generations per year.
The first generation is usually small in number and easily overlooked. The greenish, brownish, or grayish slender larvae feed on the leaflets of honeylocust and mimosa (silk tree). When disturbed, mimosa webworm larvae move quickly and violently, which helps them escape. The first-generation larvae web together two or three leaflets and feed on the leaflet undersides. This feeding causes the leaves to appear silvery at first, particularly from a distance. As damaged areas dry, they turn brown. Large numbers of first-generation infestations scattered throughout a tree call for an insecticide application to reduce the more seriously damaging second generation.
First-generation caterpillars pupate in the webbed leaves and emerge as small grayish moths. These moths mate and tend to lay eggs back into first-generation webbing. The second generation is usually much larger in number than the first. These caterpillars typically web together two to six compound leaves, causing damage that is much more obvious. Although treatment of the second generation is usually successful, considerable damage may have occurred before treatment is initiated.
Fully grown second-generation caterpillars migrate out of the webbing to pupate in protected areas such as under loose bark on tree and shrub trunks and under building siding. Many webworms pupate under siding and around windows of heated buildings where temperatures are a few degrees warmer–which explains why higher populations of mimosa webworms are found in trees near heated buildings and in years following mild temperatures.
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.