Fruitworms are pests introduced from Europe. They are the larval stages of moths of the family Noctuidae. Several species of economic importance attack fruit. These include the white striped fruitworm, Lithophane antennata (Walker); the speckled green fruitworm, Orthosia hibisci (Guenee); the yellow-striped fruitworm, Lithophane unimoda (Lentner); and the pyramidal fruitworm, Amphipya pyramidoides (Guenee).

The fruitworms’ name is derived from their habit of eating deep holes into the fruits of apple, peach, pear, cherry and plum trees. In the past few years, fruitworms have become a serious problem on apples, cherries and pears in the Missouri and Illinois in 1970. Several species occur in the north central states.

Egg: Eggs are about 0.8 mm in diameter and 0.5 mm in height. Freshly laid eggs are white with a grayish tinge. Distinct ridges radiate from the micropilar area.

Larva: Six instars occur. The larvae are generally large and robust in various shades of green marked with yellowish or whitish longitudinal stripes. Larvae are 35 to 40 mm long.

Pupa: The pupa is about 20 to 30 mm long, about 10 mm wide, and shiny.

Adult: The adults are typical noctuid moths with considerable range in color in the forewings. The forewings are dark and the hind wings much lighter. Moths are large, with wingspans of 25 to 40 mm.

Fruitworms are generally distributed throughout the United States, though the greatest numbers occur in the Northeast and Midwest. Green fruitworms attack apple, cherry, plum, pear, apricot, strawberry and quince. They also feed on a wide range of plants, including willow, birch, poplar, balsam, alder, chokecherry and maple.

The larvae feed on the leaves and fruits of deciduous fruit trees, usually newly formed apples, pears, and cherries. Most flower buds and blossoms damaged by green fruitworm larvae abort. Most fruits damaged up to and shortly after petal fall also drop prematurely. Those that remain at harvest exhibit deep, corky scars and indentations. This injury is indistinguishable at harvest from that caused by the overwintering larvae of the obliquebanded leafroller.

Omitting insecticide sprays in prebloom period or using ineffective pesticides in the prebloom sprays can increase the number of fruitworms. When natural adult fruitworm populations in wild habitats peak, they may move into commercial fruit orchards and cause damage.

With the exception of those of the pyramidal fruitworm, eggs are laid in the spring when new growth is appearing in the buds. (Eggs of the pyramidal fruitworm are laid in the fall and overwinter.) Adults of the Lithophane genus overwinter as adults and lay their eggs in the spring. The eggs of all species start to hatch when apple buds have reached the half-inch green bud stage. The young larvae feed on the unfolding leaves, and it is not uncommon to find them occupying rolled leaves in much the same manner as leafrollers. Feeding may or may not include the fruit. Where this does occur, fifth-and sixth-instar larvae will be involved. These are large, robust larvae. The feeding will take place from the time the young fruits are set or when they are about 6 mm in diameter, until they measure about 18.7 mm across. About 70 percent of the fruits attacked will not survive.

The wounds on the fruits that do survive attack gradually become sealed over with corky scar tissue that makes them unsalable. Typically, a larva will feed on more than one fruit and may damage a dozen or more. With the exception of the pyramidal fruitworm, the mature larvae drop to the soil and enter to a depth of 2 to 4 inches, construct a pupal chamber and then enter the pupal stage. They remain in the pupal stage until the following spring. Only one generation occurs annually.

The pyramidal fruitworm adults are on the wing from July until November and begin to lay eggs in late September. The eggs hatch in late April when the host leaf buds begin to swell. Larvae become full-grown about the middle of June, drop to the soil and form a prepupal larval stage in a cocoon made of silk and debris from the soil. The prepupal stage lasts about a week and the pupal stage that follows lasts about a month.

From pink sage to first cover, examine 20 fruit clusters per tree on five trees per orchard. On each tree, look for larvae or signs of fresh feeding on six fruit clusters on the outside of the tree, six clusters in the center and eight clusters near the top of the tree. Treatment is recommended if there is an average of two or more larvae per tree or evidence of fresh feeding. A commercial pheromone is available for monitoring O. hibisci adult emergence early in the season.

Sprays must be applied in the prebloom stage to prevent injury. Temperature-dependent pesticides are of limited value in the early season. Pesticides such as pyrethroids that have a negative temperature coefficient—which are more effective in cool than warm weather—work more efficiently against fruitworms earlier than later in the season.