Fruit IPM Fact Sheet Fruit IPM Fact Sheet
CRANBERRY FRUITWORM
Family—Lepidopetra
Acrobasis vaccinii
Mark Longstroth, District Extension Horticulture and Marketing Agent
References: Highbush Blueberry Production Guide—NRAES-55,
Midwest Small Fruit Pest Management Handbook, Ohio State University Extension, Bulletin
#861
The cranberry fruitworm is one of the most serious pests of blueberries in the Eastern United States. Some fields have suffered 50 to 75% losses of fruit. Earlier varieties are usually the most infested. Infested berries may be harvested and packaged without detection, resulting in consumers finding larvae in packaged berries.
Wild blueberries and cranberries are often heavily infested with the cranberry fruitworm. If commercial fields are nearby they will likely have problems with this pest. Weedy, unkept plantings are also likely to harbor high populations of this insect.
Description and Life History
This insect overwinters as
a fully grown larva within a cocoon made of silk and soil particles. The cocoons are
frequently made under weed and debris on the soil surface, but they may be deeper. The
larvae pupate in the spring and complete development, with the adult moths emerging after
bloom and fruit set. Adults are small, night-flying moths with dark grayish-brown wings;
fresh specimens have two white markings on each forewing. The eggs are deposited on the
berries, almost always on or inside the calyx cup (blossom end) of unripe fruit. Eggs
hatch in about five days.
Eggs: The eggs are very small and difficult to see without a
hand lens. They look like flat white scales with small yellowish to reddish areas near the
center. Hatched eggs appear brighter white; eggs that have been parasitized by a small
wasp appear black and will not develop into larvae.
Larvae:
In the larval stage, the cranberry fruitworm is a smooth caterpillar that is mostly green
with some brownish-red coloration on its top surface. It has three pairs of true legs on
the thorax and five pairs of fleshy prolegs on the abdomen. Larvae are about ½ inch long
when fully grown. The larvae attain a length of about 3/8 inch and are usually
greenish, sometimes light brown along the back. Once larvae are fully grown, they
drop to the ground and spin a hibernation chamber where they overwinter. There is only one
generation per year.
Adults: The adults are brownish-gray moths with a wingspan of about 5/8 inch.
Damage:
Young larvae move to the stem end of the fruit, enter, and feed on the flesh.
A single larva may feed on many as eight berries to complete its development. They move
from one berry to another within a cluster and usually web the berries together with silk.
The inner flesh of developing and ripening berries is consumed entirely by fruitworm
larvae. Fed-upon berries are covered with brown sawdust-like frass and usually webbed
together with silk. The frass of the larvae fills the tunnels in the berries cling
to the silk webbing, producing very messy feeding sites, which easily distinguish
cranberry fruit worm damage from cherry fruitworm damage. The
Monitoring:
Synthetic sex pheromones for the cranberry fruitworm have been under development for several years; monitoring the flight of adults with pheromone traps will greatly improve the timing of pesticide treatments for this pest. Experienced scouts can also monitor the calyx ends for eggs to determine the amount of egg laying, percent of egg hatch and the beginning of eggControl:
Cultural Control: Elimination of weeds and trash around plants helps by cutting down on overwintering protection for fruitworm cocoons.
Mechanical Control: Cranberry fruitworm was effectively controlled in the past by picking off infested berries, which are easily detected because of the webbing and their early ripening. This method is still practical in small plantings with light infestations.
Control by Insecticides: Clean cultivation will reduce the population of cranberry fruitworm within a field significantly, but insecticide treatments may still be needed to achieve satisfactory control of this pest. In New Jersey, university recommendations suggest making the first application when larval entries are first seen on the fruit, with a second application 7 to 12 days later in fields where the pest is a serious problem. Economic threshold levels have not been established.
