Omnivorous looper—Sabulodes aegrotata =S. caberata
The looper, or measuringworm (Geometridae), larvae chew leaves, shoots, and occasionally fruit and feed on several dozen plant species. Hosts include acacia, box elder, California buckeye, chestnut, elm, eucalyptus, fruit trees, ginkgo, magnolia, maple, pepper tree, and willow.
Young omnivorous looper larvae are pale yellow caterpillars. Older larvae grow to about 2 inches long and are yellow to pale green or pink, with dark brown, black, or green lines along the sides and a gold-colored head. In addition to the three pairs of legs behind the head, omnivorous loopers have two pairs of prolegs (leglike appendages) near the rear on abdominal segments 6 and 10. This allows them to travel in the characteristic looping manner, pulling their rear forward as they arch up their back.
Mature larvae form pearly white to brown pupae, usually in webbing between leaves. Adults are tan moths with a narrow, black band across the middle of the wing. The barrel-shaped, pale green to reddish brown eggs have a ring of tiny projections and occur in clusters on the underside of leaves.
Larvae hatch from the eggs about 8 or 9 days after oviposition, leaving behind transparent shells. Mature larvae usually pupate in webbing between leaves. Pupation lasts 1 to 4 weeks. Adults (moths) are active at night.
Populations increase with increasing temperatures in spring. Depending on temperature, egg-to-adult development takes 2 to 5 months. Omnivorous looper has four to five generations per year in warmer, inland locations and three generations per year in coastal areas.
Omnivorous looper leaf damage is especially evident on terminal shoots. Young larvae chew the leaf surface, leaving a brown membrane. Older larvae chew entirely through edges of leaves or shoots or between leaves tied with silk, often leaving only the midrib and larger veins.
Fruit damage can be caused by young or old larvae. If young fruit is fed on, it sometimes becomes misshapen. Chewing typically scars the fruit surface and may cause damaged fruit to drop.
Conserve natural enemies that can biologically control omnivorous looper. Avoid applying broad-spectrum, residual (persistent) insecticides to plants. Omnivorous loopers thrive in more protected sites, so pruning and thinning canopies can substantially reduce caterpillar abundance and damage.
Birds, predatory bugs, lacewing larvae, and spiders prey on the caterpillars. A granulosis virus often infects and kills larvae when they become abundant.
Parasitic wasps, especially Trichogramma egg parasites and three larval parasites (Braconidae), are the most important natural enemies of omnivorous looper. Apanteles caberatae and Meteorus tersus feed as a single wasp larva inside a looper larva, then emerge to pupate near the caterpillar. Apanteles caberatae pupates in an elongated, whitish, silken cocoon attached to foliage near its dead host. Meteorus tersus pupates in a brown or yellowish, parchmentlike cocoon that sometimes hangs beneath leaves or twigs, suspended on a silken thread about 1 to 2 inches long. Habrobracon (=Bracon) xanthonotus females lay from one egg to several dozen whitish eggs on each caterpillar. The emerging larvae feed as pale greenish to yellow maggots attached to the looper.
Controls include thoroughly spraying infested foliage with Bacillus thuringiensis (Bt). Spraying spinosad is also effective, but can adversely affect certain natural enemies. Spinosad is toxic to bees for several hours after the spray has dried, so do not apply it to plants that are flowering.
Omnivorous looper late-instar larva
Chewed leaf and pupa (top) in webbing