Most susceptible tree species are mulberry trees (Molus sp.) and ash-leaved maple (Acer negundo). In Europe, the fall webworm always has 2 generations per year which prevents it going to the north. In North America it has both monovoltine populations in Canada and Maine, and bivoltine populations to the south.
I studied population dynamics of the fall webworm, its predators and parasitoids in Moldova, Ukraine, and in Russia (North Caucases) (see my list of publications). Please contact me if you need reprints of my papers. Most of them are in Russian, but several papers were translated in English.
Below find some photographs (click to see the full-size picture!) of the fall webworm:
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Adult moths are white. Females lay up to 1500 eggs on the lower surface of the leaf. |
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Small larvae skeletonize leaves. Mostly they sit on the lower surface of the leaf. |
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Some times larvae can be found on the upper surface of the leaf. |
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More small larvae. |
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Large larvae eat the entire leaf. |
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Large spin cocoons mostly under bark flaps and pupate there. The picture shows pupae under the bark flap. |
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Gregarious parasitoid Psychophagus omnivorus (Pteromalidae) is a very effective natural enemy which attacks pupae. This is a native polyphagous parasitoid which prefers to parasitize Fall webworm pupae. I developed methods for rearing these parasites on alternative hosts, and released them for biological control of the fall webworm. |
| Typical damage of a young maple tree caused by the fall webworm. |