Green fruitworms—various species
At least ten species of similar-looking, commonly green caterpillars (noctuids, family Noctuidae) are sporadic pests of trees including apple, citrus, pear, and stone fruits. The most common of the green fruitworms are citrus cutworm [Egira (=Xylomyges) curialis], humped green fruitworm (Amphipyra pyramidoides), and speckled green fruitworm (Orthosia hibisci).
Identification
Young larvae are pale green caterpillars and generally not distinguishable to species. Older green fruitworms commonly have green heads and bodies and markings that help to distinguish the species, but the coloration is variable.
Citrus cutworm. The adult (moth) has dark gray forewings and whitish hind wings. Their length is about 3/4 inch and the wingspan is about 1-1/2 inches. The larvae are mostly brown, gray, green, or pinkish and grow to about 1 inch long. Except for the youngest larvae, citrus cutworm larvae have a continuous, whitish, lengthwise stripe along each side of the abdomen, head, and thorax.
Humped green fruitworm. Adults have mottled forewings that are mostly brown or grayish with blackish markings. The hind wings are coppery to orange, unlike citrus cutworm that has whitish hind wings and speckled green fruitworm that has grayish to silver hind wings. The adult humped green fruitworm has a wingspan of 1-1/2 to 2 inches. Larvae are bluish green or green and grow to about 1-1/2 inches long. They have a bright yellow, longitudinal line along each side and a whitish line along the top. Their last segment has a prominent hump for which they are named. Larvae are pictured at the end of this webpage.
Speckled green fruitworm. Adults have mottled forewings that are mostly brown, grayish, or reddish brown with blackish markings. The hind wings are gray to silver. Their wingspan is about 1-1/2 inches. Larvae are various shades of green and grow to about 1-1/2 inches long. They have cream-colored to yellowish, longitudinal lines along the back and sides.
Note that California pear sawfly resembles some larvae of green fruitworms. Noctuid larvae such as green fruitworms have five pairs of prolegs (fleshy appendages) in the middle of their abdomen, one pair on each of segments three to six. California pear sawfly has six pairs of prolegs in the middle of the abdomen, on segments two to seven. Prolegs help distinguish caterpillarlike insects of various types.
Life cycle
Noctuids develop through four life stages: egg, larva, pupa, and adult. After hatching, the larvae develop through five increasing larger instars. Larvae are present from leaf flush through petal fall and when young fruit are on the tree. The youngest larvae chew and feed during the day. Older larvae feed at night and hide during the day.
Eggs are laid on leaves or twigs. Adult females of citrus cutworm and speckled green fruitworm lay their eggs in the spring after overwintering as adults. Adult female humped green fruitworms lay eggs in fall and overwinter as eggs. These species have only one generation per year.
Damage
Young green fruitworm larvae feed on leaves and blossoms and sometimes on young fruit. Fruit feeding begins as soon as fruit are present, about petal fall, and continues until larvae have completed their development. Severely damaged fruit drop prematurely. If chewed fruit remain on the tree at harvest time, they have distinct roughened, russeted (brownish) cavities where the chewing earlier occurred. Chewed fruit may also grow misshapenly.
In addition to being sporadic pests of tree fruits, some of these green fruitworms can also feed on numerous other broadleaved plants but rarely if ever are abundant enough to be pests on them in California. For a complete list of plants on which they have been found to feed see the information for humped green fruitworm and speckled green fruitworm in HOSTS - a Database of the World's Lepidopteran Hostplants. By comparison citrus cutworm feeds mainly on citrus.
Solutions
Certain parasitoid (parasitic) wasps including Cotesia (=Apanteles), Eulophus, Meteorus, and Ophion species help keep green fruitworm abundance at low levels during most years unless disrupted by the application of broad-spectrum, persistent insecticides.
Trichogramma species egg parasitoids commonly kill the eggs. In some locations a fungal pathogen sometimes kills green fruitworm pupae. Predators of the adults or caterpillars include assassin bugs, ground beetles, larvae of green lacewings, and spiders.
Control ants, reduce dust (e.g., periodically hose off small plants), and avoid the application of broad-spectrum insecticides for all pests on the trees to increase the effectiveness of natural enemies. See Protecting Natural Enemies and Pollinators for more tips on conserving parasitoids and predators.
Green fruitworms generally do not warrant control action on residential fruit trees. By the time fruit grow large enough for feeding damage to become apparent, green fruitworm caterpillars are usually no longer present. If caterpillars are abundant and their damage during previous seasons has been intolerable, Bacillus thuringiensis (Bt) or spinosad can be sprayed to thoroughly cover infested plant parts. Add horticultural oil to the spinosad to increase its persistence and to control moth eggs and other pests directly contacted by the spray.
Avoid applying spinosad to plants in bloom because it is toxic to honey bees and some natural enemies. If applying Bt, make a second application about 7 to 10 days after the first because Bt is not persistent and not all the green fruitworms may be in stages susceptible to Bt at the same time.
Adapted from Integrated Pest Management for Citrus and Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, University of California Statewide Integrated Pest Management Program (UC IPM). |
