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Extension Entomology

Mimosa Webworm

–by Dr. Raymond Cloyd

Mimosa webworm (Homadaula anisocentra) larvae (=caterpillars) are now feeding and creating protective habitats on honeylocust (Gleditsia triacanthos) and mimosa (Albizia julibrissin) trees, which are quite noticeable in the Manhattan (KS) area. The larvae (=caterpillars) are 1/2 inch long when fully-grown (Figure 1),

Fig 1. Mimosa Webworm Caterpillars Feeding On Leaves (Auth–Raymond Cloyd, KSU)

Fig 2. Mimosa Webworm Webbing On Branch End (Auth–Raymond Cloyd, KSU)

Webbing commonly starts at the tops of trees and serves to protect caterpillars from natural enemies (parasitoids and predators) and insecticide spray applications. Heavily-infested trees are brown or scorched in appearance (Figure 3) as the caterpillars skeletonize the leaf tissue. Caterpillars eventually fall from trees on a silken strand before pupating. Mimosa webworm pupates in bark crevices or pupae are glued to structures (e.g. buildings).

Fig 3. Mimosa Webworm Feeding Damage (Auth–Raymond Cloyd, KSU)

In regards to controlling mimosa webworm infestations, it is probably too late although initial damage may be minimal. Insecticides that can be used to suppress mimosa webworm populations, in which the caterpillars are exposed, include: acephate (Orthene), Bacillus thuringiensis subsp. kurstaki (Dipel), spinosad (Conserve), and several pyrethroid-based insecticides (e.g. bifenthrin, cyfluthrin, and permethrin). Read the label of each product to ensure that “webworms” are listed. High-volume spray applications are required to contact the caterpillars inside the protective webbing. If trees are already heavily-infested with webbing then it is too late to apply an insecticide. If possible, selective pruning can quickly remove isolated or localized infestations of mimosa webworm.

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