Lesser maple spanworm
Damage, symptoms and biologyThe lesser maple spanworm is widely distributed in the Maritime Provinces, southern Quebec, and southern Ontario, wherever red maple, its principal host, grows. Populations of this native insect remained low until a serious eruption occurred in the mid-1970s in central and southern New Brunswick. In those regions patches of damage appeared in areas where the spanworm, often in association with other defoliators such as the fall cankerworm and a common leaf roller, caused moderate to severe defoliation of red maple. That unprecedented outbreak was especially severe in forest stands but ornamentals were also damaged. Although sugar maple is also attacked, it appears less prone to injury.
The adults are white moths with a wingspan of about 25 mm. The front edges of the forewings are marked with 3 or 4 golden brown spots and 2 or 3 very thin, often indistinct, transverse stripes of the same colour. They first appear about July 9 and reach peak emergence in mid-July. The moths mainly rest during the day and fly in the evening. The eggs are grey to pink and are laid singly on the branches and trunk of host maple trees. They overwinter and hatch in late May and early June. The larvae are green-headed loopers with a green body and contrasting narrow white, cream, or yellowish lines. Fully grown they average 20 mm in length. The developing larvae feed mostly during June. They are voracious feeders and can consume all the green portions of leaves, leaving only the main veins intact. Feeding in shade trees is usually characterized by the presence of numerous holes in the leaves and by large indentations on their edges. Pupation begins in late June or early July and usually lasts about 10 days.
Other informationOwners of red and sugar maple trees should inspect them during the first 10 days of June for small green larvae feeding on leaves.
Canadian Forest Service Publications
Diet and feeding behaviour
: Feeds on the leaves of plants.
- Free-living defoliator: Feeds on and moves about freely on foliage.
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