Oriental fruit moth—Grapholita molesta
Oriental fruit moth (a tortricid, family Tortricidae) during its larval (caterpillar) stage is a pest of almond nuts and stone fruits. Nectarines and peaches are especially susceptible to its damage.
The presence of Oriental fruit moth or other tunneling larvae may not become obvious until harvesttime. Shoot damage is easily overlooked and that from Oriental fruit moth is the same as shoot damage from peach twig borer. Oriental fruit moth damage to nuts and fruits is the same as that of codling moth. All three of these pests can be present in the same tree.
Larvae of Oriental fruit moth are orangish, pale yellow, pink, or whitish with a brown head. They grow up to 2/3 inch long. Unlike many other caterpillars, they do not produce silk webbing during their feeding, but mature larvae do form silken cocoons in which they pupate. To distinguish Oriental fruit moth from similar larvae, use a hand lens to examine the underside of the last abdominal segment for a row of short, stiff bristles (anal comb); other larvae that tunnel in almond and stone fruits lack this anal comb.
Adults are easily overlooked because they are inactive during the day and difficult to observe around twilight when they fly. Adult Oriental fruit moths are about 1/2 inch long and dark brown or gray with whitish mottling.
Eggs occur mostly on the upper surface of leaves and on young shoot tips. Eggs are disk-shaped, cream to white when first laid, and about 1/30 inch (0.8 mm) in diameter. Before hatching, the dark head of the developing larva becomes visible through the eggshell.
Pupae are oblong, brown to orangish, and about 1/2 inch long. They occur within a tightly woven silk cocoon in or near plant parts where they fed as larvae or in bark crevices or organic debris on the ground.
Oriental fruit moth develops through four life stages: egg, larva, pupa, and adult. Overwintering is as diapausing (inactive) prepupae (mature larvae) inside cocoons in protected places on the tree or in organic litter near the tree base. In early spring, pupation occurs inside the cocoon. Adults emerge in February or early March and mate.
Adult females in late winter and spring lay eggs on leaves or young shoots and the larvae feed and tunnel inside shoot tips. Larvae of subsequent generations may tunnel in shoots or green (young) fruits or nuts. As fruit and nuts mature, they become the larvae's preferred site of feeding and tunneling. Oriental fruit moth has five or six generations per year in California.
Larvae bore into twig terminals and young shoots. This causes shoot tips to wilt and die back one to several inches from the tip (called flagging or shoot strikes). Healthy trees tolerate dieback from shoot tunneling; this damage is not important except that it indicates later generations of this pest may damage fruits and nuts. An exception is that shoot regrowth on heavily infested young trees can cause trees to develop poor structure.
The important damage occurs when later-generation larvae chew and tunnel in the center of green or ripening fruits or nuts where they feed around the pit or seed. If management action might be taken, first confirm the cause of damage by identifying the larvae. Do this by inspecting the underside of the last abdominal segment of several larvae. For larvae that tunnel in almond nuts or stone fruit fruits, an anal comb is present only on Oriental fruit moth larvae.
A wasp, Macrocentrus ancylivorus, is a common and important parasitoid (parasite) of larvae of oriental fruit moth and peach twig borer. On trees not sprayed with persistent, broad-spectrum insecticides, 80 to 90% of the larvae are commonly parasitized by Macrocentrus by August or September. This provides long-term biological control.
Growing a small plot of sunflowers without harvesting their heads (seeds) provides Macrocentrus an overwintering host, the sunflower moth (Homoeosoma electellum). This can increase the early-season abundance of Macrocentrus in fruit and nut trees the following season. Planting sunflowers in a staggered planting in April and again in late May can be a useful strategy.
Mating disruption is very effective for the pest's first two generations and into the third generation in relatively large commercial orchards. Mating disruption may not be effective in residential trees when conducted on only one or a few trees.
Oriental fruit moth and other fruit- and nut-boring larvae are difficult to control with insecticides. Effective products are available only to professional pesticide applicators. In commercial orchards multiple applications of mostly persistent, broad-spectrum insecticides must be carefully applied by timing applications with the use of sticky traps baited with pheromone (sex attractant) and monitoring of degree-days (heat accumulation). The use of degree-days, mating disruption, and pheromone traps are described in the UC IPM Pest Management Guidelines: Peach.
Adapted from the publication linked above and Integrated Pest Management for Stone Fruits 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).