How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

Orange tortrix (family Tortricidae) is an uncommon problem on avocados grown in coastal areas. It rarely is injurious at inland growing areas. Orange tortrix feeds on various weeds and crops including citrus, grape, and strawberry.

Orange tortrix and amorbia adults resemble each other. They are orangish to tan moths with dark shading across their folded wings. At rest, their folded wings flare out at the tip so their overall shape resembles a bell. Orange tortrix adults are about 0.4 inch long, about one half the size of amorbia adults.

Orange tortrix and amorbia females lay eggs overlapping in a mass. Orange tortrix oviposits on the surface of young leaves, green twigs, or green fruit. Each egg is pale green, flat, oval, and has a finely reticulated surface. Females lay several clusters that range from a few eggs to over 150 eggs per mass. Eggs hatch in about 9 days.

Larvae usually feed singly on shoot tips or on succulent leaves in nests they web together with silk. Larvae develop through 5 to 7 instars over about 40 days. They are about 0.08 inch (2 mm) long at hatching and about 0.5 inch long when mature. Larvae have a brownish or straw-colored head and prothoracic plate (the top of first segment behind the head). The variable body color is dark gray, greenish, straw-colored, or tan. Orange tortrix and amorbia larvae typically wriggle vigorously backwards or sideways when disturbed. Orange tortrix may drop to the ground or remain suspended from the leaf on a silken thread.

Larvae form a dense silken cocoon where they pupate within webbed foliage. Adults emerge in about 1 to 3 weeks, depending on temperature. Orange tortrix has two to four generations per year, with all stages present throughout the year.

DAMAGE

Most larval chewing occurs within silken webs on outer-canopy shoots. During bloom, tiny larvae sometimes feed among flowers. Larvae also feed on green bark, girdling some twigs. White exudate may cover wounds on larger twigs. Least common is fruit feeding, but this is the economic damage. Fruit injury closely resembles damage from other avocado caterpillars, except that orange tortrix tends to chew deeper holes. Feeding near the stem end of fruit and on the stem may cause fruit to drop.

MANAGEMENT

Conserve natural enemies, which usually keep caterpillars below damaging levels. Modify cultural practices to reduce pest reproduction and survival. Avoid applying broad-spectrum or persistent insecticides for any pests. Caterpillar outbreaks commonly occur after spraying carbamate or organophosphate insecticides, which poison parasites and predators. When pesticides are warranted, limit application to the most infested spots to provide refuges from which natural enemies can recolonize after treatment.

Biological Control
More than one dozen parasite species and various predators attack orange tortrix, including assassin bugs, birds, damsel bugs, lacewings, and pirate bugs. These usually provide excellent biological control. Parasites include Trichogramma platneri and several tachinid flies as described in the section AMORBIA. Common internal larval parasitic wasps are Apanteles aristoteliae (family Braconidae) and Exochus spp. (Ichneumonidae).

Organically Acceptable Methods
Biological controls and sprays of Bacillus thuringiensis are acceptable for use on an organically certified crop.

Monitoring and Treatment Decisions
Where caterpillar problems may occur, monitor during at least spring and summer. Good places to monitor include where bright lights such as security lights are used outdoors because the nocturnal moths are attracted by lights to lay eggs nearby. Be sure to correctly distinguish the cause of any damage as other insects and certain abiotic disorders cause leaf holes resembling caterpillar chewing. Correctly identify the species of caterpillars. Alternate host plants, damage potential, monitoring methods, and natural enemies vary depending on the species of caterpillar. Look for caterpillar predators and larval diseases and parasitism. Natural enemy prevalence affects treatment decision making. See MONITORING CATERPILLARS AND THEIR NATURAL ENEMIES for details on identification and monitoring methods including inspecting foliage for caterpillars and their damage (timed counts), trapping adults, shaking foliage to dislodge larvae (primarily for avocado looper), or a combination of these methods.

There are no established thresholds, and treatment for orange tortrix is rarely warranted. If sprays are needed, use Bacillus thuringiensis when larvae are small. Spraying with malathion often leads to outbreaks of other pests and is not recommended.

IMPORTANT LINKS

• Photos of caterpillars and their damage
• Photos of natural enemies of caterpillars

PUBLICATION

UC IPM Pest Management Guidelines: Avocado
UC ANR Publication 3436
Invertebrates
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura County
B. A. Faber, UC Cooperative Extension, Santa Barbara/Ventura counties
J. G. Morse, Entomology, UC Riverside
M. S. Hoddle, Entomology, UC Riverside
Acknowledgment for contributions to Invertebrates:
M. Blua, Entomology, UC Riverside
P. Oevering, UC Cooperative Extension, Ventura County
D. Machlitt, Consulting Entomology Services, Moorpark, CA
T. Roberts, Integrated Consulting Entomology, Ventura, CA
B. B. Westerdahl, Nematology, UC Davis

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