The cranberry fruitworm (Acrobasis vaccinii Riley) is common throughout the eastern United States and Canada. It may be found on a variety of small fruits including cranberry, blueberry, and huckleberry. The adults are small, brownish gray moths with a 16-18 mm wingspan (5/8 to 3/4 inch); they are seldom seen because they are active only at night. Larvae are smooth, elongate caterpillars with three pairs of thoracic legs near the head and five pairs of fleshy prolegs along the abdomen. They are usually pale yellow-green in color, but may turn a light pink on the dorsal surface as they mature. Fully grown larvae reach about 15 mm in length (5/8 inch).
- Adult stage of the cranberry fruitworm.
- Larval stage of the cranberry fruitworm.
- Frass and webbing around infested fruit.
Life Cycle and Seasonal Distribution
Adult moths emerge and mate very early in the spring, about the time blueberry buds start to open. Females lay their eggs on green berries that are just beginning to develop; the oviposition site is usually located near the edge of the calyx cup. First instar larvae hatch in four to five days, burrow into the berry, and feed on the pulp. As larvae grow, they move from berry to berry within a cluster leaving behind a trail of frass (excrement) and silk. Fully grown larvae drop to the ground and spin silken chambers under blueberry plants. They pass the summer, fall, and most of the winter as larvae inside these hibernacula, then pupate in late January or February. There is usually only one generation per year, although a few individuals may continue to develop and produce a second generation on deerberry (Vaccinium stamineum L.) in July (Neunzig 1972).
Symptoms and Damage
Larvae feed inside a berry until most of its contents have been consumed. The infested fruit usually becomes filled with brownish frass (excrement from the insect), then shrivels, and turns prematurely blue. As larvae move from one berry to another, they spin a web of silk and frass that gradually entwines all of the surrounding fruit and makes the entire cluster unsuitable for harvest (Fulton 1946).
Both egg and larval parasites have been associated with the cranberry fruitworm (Maxwell and Morgan 1951, Neunzig 1972). Phanerotoma franklini is the most common of these species, but it has never been found in densities high enough to provide effective control.
Scouting, Management, and Control
As they emerge in the spring, adult moths of the cranberry fruitworm can be attracted to black-light traps (UV). This technique will not provide adequate control by itself, but it helps optimize the timing of insecticide applications (Tomlinson 1962). Larval infestations can be detected by looking for the pin-sized entry hole near the stem of small, shrunken berries that have turned blue. The distinctive frass and webbing produced by this species does not usually appear until the larvae are several weeks old and begin moving between berries.
Fruitworm populations that exceed one infested cluster per five plants should be sprayed immediately. A second application in 10-14 days is usually needed for complete control of the young larvae. Continue scouting for at least two weeks to avoid possible reinfestation.
- Fulton, B. B. 1946. Dusting blueberries to control the cranberry fruitworm. J. Econ. Entomol. 39: 306-308.
- Neunzig, H. H. 1972. Taxonomy of Acrobasis larvae and pupae in eastern North America (Lepidoptera: Pyralidae). USDA Tech. Bull. 1457. 158 pp.
- Maxwell, C. W., and C. T. Morgan. 1951. Life history studies of the cranberry fruitworm, Mineola vaccinii (Riley), in New Brunswick. Ann. Rep. Entomol. Soc. Ontario. 82: 21-25.
- Tomlinson, W. E. 1962. The response of the cranberry fruitworm to black light. J. Econ. Entomol. 55: 573.
Last updated: 2 June 1997
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