Integrated Pest Management Guide

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CRANBERRY FRUITWORM, Acrobasis vaccinii (Riley)

Pest Status: Cranberry fruitworm is present in Washington and may be present in British Columbia.

Life cycle and feeding habits: The fruitworm spends the winter in the larval stage, wrapped in a hibernaculum made of old leaves, sand, soil and other material under vines on the bed floor. Pupation occurs in spring and the moths begin to appear in the middle of June. Generally, peak flight occurs about the same time cranberries are in full bloom and may continue through much of July.

The moths are dark brown with very noticeable white bands on the forewings and have a wingspan of about 1.5 cm (2/3 inch). They rest under the vines during the day, particularly during bright sunshine. When disturbed, they fly 15 - 17 metres (40 - 50 feet) before coming to rest on the vines. Moths are strong fliers, moving readily between cranberry beds and alternate hosts such as highbush blueberries.

The eggs are generally laid on the calyx end of the cranberry. When the larva hatches, it usually crawls to the stem end, chews into the berry, and seals its entrance hole with a white silken web. Only very close inspection will reveal that the berry has been attacked. The larva is pale green with a yellowish head. Larvae have three pairs of front legs and five pairs of hind legs. When fully grown, a larva is 1.3 cm (1/2 inch) long. It rarely leaves a berry until it has eaten all the pulp and seeds, and filled the berry with frass (excrement). Usually it leaves the berry by boring through the side and into an adjoining berry. One larva may eat three to six berries before going into diapause (a dormant, hibernation-like state) in the trash for the winter. Infested green fruits redden, then shrivel up like raisins.

Monitoring: Male moths are attracted to traps baited with cranberry fruitworm pheromone. In Massachusetts, egg-laying begins when berries have just begun to grow, and may continue to late August. Females prefer to lay eggs on berries larger than pinhead stage. Studies in Massachusetts demonstrated that female moths wait for the fruit to expand before they began laying eggs. The phenology of the cranberry plant gives a good estimate of the time of egg-laying. Work in Massachusetts showed that most eggs are found at the calyx end of berries from edges of beds and ditches, in weedy areas, and on berries that stick up above the vine canopy. If possible, 25 - 50 berrries from these areas should be examined under a magnifier or microscope to look for eggs.

Control: If eggs are found during monitoring, a registered insecticide should be applied. Insecticides should not be applied during bloom or against fruitworm larvae, which are protected in the berries.

In the eastern U.S.A., the holding of late water (equivalent to a spring reflood) has been used for over a century to control cranberry fruitworm. Research on biological control of cranberry fruitworm is underway in Quebec.


Cranberry fruitworm moth (photo courtesy of J.-F. Landry)	Cranberry fruitworm larva (photo courtesy of J.-F. Landry)