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Recent Mahogany Webworm Attacks

mahogany_webworm06 Mahogany webworms have been busy defoliating West Indies mahogany trees in the Upper Keys this spring. The colorful yellow, black and white striped caterpillars of this moth species also produce extensive webs. The adult moth is dull and brown.
The larvae of Macalla thyrsisalis Walker are active for about 10 days during the period of spring flush and leaf expansion. They feed primarily on immature leaves. These insects are not seen the rest of the year.
Although these pests are messy and do extensive damage, these conditions are temporary and do not have a lasting effect on the health of the host trees. The insects are kept under control naturally by parasitic wasps and and a parasitic fly.
Various insecticides were found to be lethal to mahogany webworms under laboratory conditions, but spraying large trees with insecticides, whether in urban or rural areas, may involve unacceptable health and environmental hazards. Spraying mahogany foliage with a neem product, which is a safer option, was found to be effective in preventing mahogany webworms from consuming foliage when applied just before the appearance of larvae in the spring, or when they were in early instars.

2 Comments on “Recent Mahogany Webworm Attacks

  1. Hi Paul,
    Thank you for the question. I am the new horticulture agent since Kim Gabel retired. Imidacloprid, which is a neonicotinoid, is not effective against lepidopterans (caterpillars). You could try Spinosad or a microbial insecticide with the active ingredient Bacillus thuringiensis, the strain specific to caterpillars. These will need to be sprayed early, at the first sight of an infestation. Bt is only effective against caterpillars and will not harm beneficial insects. Always follow label directions when using any pesticides. Please contact our office if you have any additional questions.

  2. Will injecting Mahogany Trees with Imidacloprid prevent the the annual infestation of webworms? If it is applied as an injection, is it harmful to bees and/or are there other environmental issues?
    I know webworm presence on the Mahogany trees will pass with little harm to the trees, but they do create a mess and my neighbor gets quite upset.