Amorbia—Amorbia cuneanum =A. cuneana
Amorbia (a tortricid, family Tortricidae), also called western avocado leafroller, is primarily a pest of avocado. It sporadically damages citrus, mostly when grown near avocado. Other hosts include bay laurel, hollyleaf cherry, madrone, manzanita, photinia, and pyracantha.
Amorbia adults (moths) are bell shaped at rest as is typical for tortricid moths. Their variably colored forewings are mostly orangish to tan with dark markings. Adults are about 1 inch long, about twice the size of the similar-looking adult orange tortrix.
The eggs are disk shaped and pale green. They are laid on leaves in an overlapping mass of 5 to 50 eggs, resembling fish scales. Larvae (caterpillars) are yellowish green when young. They become darker green as they mature and grow up to 1 inch long. Amorbia larvae can be distinguished from all other caterpillars in avocado and citrus by the dark horizontal line on each side of the larva's head and another line above the first pair of legs. As with larvae of orange tortrix and other tortricids, amorbia larvae commonly wriggle repeatedly and drop suspended on a silk thread when disturbed.
Pupae are 1/2 to 3/4 inch long and usually occur in leaves rolled by the larvae. Initially pupae are pale green, gradually turn tan, and become brown shortly before the adult emerges.
Amorbia develops through 4 life stages: egg, larva, pupa, and adult. The adult female lays about 150 to 200 eggs during her 2 to 3 week life span. After hatching, larvae develop through 5 increasingly larger instars. Larvae (caterpillars) prefer to feed on new growth flushes but will also chew older leaves and fruit. They roll and tie leaves together with silk or tie leaves to fruit and feed within this protected shelter. After petal fall, young larvae will feed underneath the calyx on fruit rinds. Mostly where fruit touch other fruit or leaves, older larvae will also chew on the peel of fruit and sometimes into the flesh.
Amorbia develops through 2 to 3 generations a year in Southern California and the San Joaquin Valley. Adult flights generally occur in the early spring, midsummer, and autumn.
Otherwise healthy trees tolerate extensive larval feeding on leaves. Where young larvae have fed under or around the fruit calyx, rinds develop discolored scars that resemble the feeding damage of avocado thrips or citrus thrips. Amorbia scarring of fruit rinds can be deeper than that of thrips. Elsewhere on avocado rinds, the feeding scars of amorbia are commonly circular. This damage is just aesthetic and does not affect the internal quality of fruit. Older larvae may also chew holes through the fruit rind or skin, causing fruit to become unappetizing or colonized by decay microorganisms.
Numerous natural enemies can keep amorbia abundance and damage low unless disrupted by the application of broad-spectrum insecticides. Natural enemies include tachinid flies, some of which lay their oval white eggs externally on caterpillars. The most important natural enemies of caterpillars are parasitic wasps such as Brachymeria ovata and Hyposoter exiguae. Many of these parasites also prey on other caterpillar species that can be present such as omnivorous looper and orange tortrix. Tiny, egg-parasitic Trichogramma wasps parasitize and kill the eggs. Eggs parasitized by Trichogramma become black to dark, unlike the lighter color of unparasitized eggs.
Control ants, reduce dust (e.g., periodically hose off small trees), and avoid the application of broad-spectrum insecticides for all pests on avocado and citrus trees to increase the effectiveness of natural enemies. See Protecting Natural Enemies and Pollinators for more tips on conserving natural enemies.
Pruning trees to minimize dead twig and plant debris accumulation in canopies reduces the hiding places for amorbia and helps to reduce its abundance. Where fruit is excessively abundant, removing some of the fruit in a cluster also reduces caterpillar hiding places and contributes to the remaining fruit growing larger. Control weeds because some of these can host amorbia and other species of caterpillars that move to fruit trees as adults.
Where caterpillar chewing on fruit has been a problem during the previous growing seasons, monitor trees once fruit is present. Inspect foliage and fruit that touch other fruit or leaves in the outer canopy and look for caterpillars, chewing damage, rolled leaves, and silk webbing.
If only a few caterpillars or their egg masses are found, these can be crushed or the infested foliage clipped off and disposed of in the trash. If caterpillars are abundant, Bacillus thuringiensis (Bt) or spinosad can be sprayed to thoroughly cover outer canopy foliage. Adding horticultural oil to the spinosad can increase its efficacy persistence and also control moth eggs and certain other pests that are directly contacted by the spray. Avoid applying spinosad to plants in bloom because it is toxic to bees and certain natural enemies.
Adapted from Integrated Pest Management for Avocados and Integrated Pest Management for Citrus, University of California Statewide Integrated Pest Management Program (UC IPM).
Adult amorbia are tan to orangish moths with black markings.
Eggs are disk shaped and overlap like fish scales.
Larvae of amorbia have a dark mark on the side of the head and another above the first pair of legs.
Citrus fruit chewed by an amorbia larva where it is webbed to a leaf.
Avocado foliage chewed by amorbia.