Oriental Fruit Moth (OFM) in Stone Fruit

Introduction

Oriental fruit moth (OFM; Grapholita molesta Busck), native to China, was introduced to the US in 1913 from flowering cherry trees imported from Japan. Since then it is found in all fruit growing regions of the US, southern Canada and northen Mexico. It is also found throughout Europe, Asia, Australia and South America. OFM larvae bore into shoots and feed in fruit making it a serious quarantine pest of stone fruit destined for markets such as Mexico or British Columbia, Canada that maintain OFM-free regions. All stone fruit packed for shipment to those markets must be inspected and be certified as being free of OFM in accordance with the applicable export work plan. Each facility planning to ship fruit to those markets must have employees trained and certified annually by officials authorized by the US plant protection organization (USDA/APHIS/PPQ). Fruit on the packingline or in the orchard must be inspected for any internal feeders, but especially for OFM. At every packing facility each day 300 cull fruit per lot must be cut and examined by a certified employee. Prior to shipment, 2% of the boxes for each fruit lot must be examined by an inspector authorized by APHIS. At least 5 fruit per inspected box must be cut and examined for internal feeders. Once a shipment arrives at the border, authorities of that nation will inspect an additional 2% of the cartons, cutting 1% of those fruit.

ofm-lc_cushman_usda_5006027-lgptOFM Life Cycle

OFM overwinters as a fully grown larva protected within a silk cocoon called a hibernacula located in tree crevices or in the orchard ground cover.
OFM pupates in the spring with this overwintering generation emerging around the time of peach blossom. This first peak moth emergence is typically late April to mid-May. Eggs are laid on foliage, usually on the upper side of terminal leaves. Females can lay up to 200 eggs. Incubation can take between 5 and 21 days depending on temperature.
After hatching, 1st generation larvae bore into growing shoots. The 1st instar larvae are very tiny and difficult to see. The 1st instar larvae is initially noticed by detecting the dark head capsule (see gallery below). Larvae size starts at about 1.5 mm (1/16th inch) and grows to 8 to 13 mm (3/8th to 1/2 inch) as a 4th or 5th instar larvae, depending on generation.
First generation larvae reach maturity by mid- to late May, depending on temperature. The 1st generation moth flight is from early June through mid-July.
There can be 3 to 4 moth flights per year in Washington state (1 for each completed generation) depending on accumulated heat units in the area found.
Some 2nd, and most 3rd and 4th generation larvae attack fruit before seeking overwintering sites where they spin a silk cocoon (hibernaculum; see gallery below)).
OFM larvae are typically cream to pink in color with a dark head capsule, except just after molting (see gallery below).

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OFM Shoot Damage

The majority of the damage to shoots comes early in the season before fruit are present. As the temperatures increase in early spring overwintering larvae complete development and emerge as moths. Soon afterwards, the first eggs are laid on the new shoot growth. Newly hatched larvae bore into the shoots and tunnel down the stem. Initially, the top leaves wilt. Gradually, the feeding damage causes tip die-back and leaf death. Upright twigs with one small wilted leaf usually means a larva has entered within the last day or two. When a larva has used up all the food source in a stem or is ready to pupate, it will chew an exit hole in the stem. Exit holes can be detected from the gummy ooze leaking from the hole. If a twig is dark or has dry leaves and gummy ooze, the larva has already exited.
Note: First and second generation larvae tend to mainly damage shoots; most of the fruit injury is due to third and fourth generation larvae.

ofm-shootdamage_jjhamann_5545232-lgpt

Monitoring orchards for OFM infestation begins early in the season with placement of OFM-specific pheromone traps. The traps will detect when the first moths of the year begin to fly. Monitoring moth flight helps determine when to begin treatments of eggs and newly hatched larvae. Field scouts will also look for signs of infestation by looking for wilted leaves and presence of dead leaves at the top of shoots referred to as ‘flags’. Trap monitoring continues throughout the season to monitor for later generation moths.

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Fruit Damage

External

Fruit can be damaged both externally and internally. External damage occurs when larva feed on the outer surface. As they feed, the damaged tissue leaks and becomes gummy. Bacteria and mold will gradually set in leaving black deposits. If severe external feeding occurs early in the season, the fruit may drop. Late season surface feeding will leave the fruit scared.

Internal

There are two types of internal feeding. Type one is caused by the larva entering the fruit by way of an entrance hole. There may or may not be signs of external feeding beyond the actual entrance hole. Having a visible entrance hole makes it easier to detect OFM infestation.
However, OFM larva may enter the fruit directly via the stem, making their entry virtually invisible. This is often referred to as Type 2 internal damage. Their may be extensive internal feeding, but externally the fruit may look normal. This is why export protocols often call for a random sampling of seemingly uninfected fruit to be cut and examined for internal infestation.

Similar Insect Damage

There are a variety of other insects that attack apricots, peaches and nectarines in the Pacific Northwest. The peach twig borer is the closest in both appearance and in the type of damage it causes. Ways to distinguish the larvae will be shown in the next section, but an example of the damage is in the gallery below.
Other insects that can cause similar external damage include leafrollers, cutworms, codling moth and even thrips. Although codling moth is rarely found in stone fruit, some damage may occur if there is a heavy population in a nearby apple orchard. Examples of damage caused by various other insects are shown in the gallery below.
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OFM Identification

Larvae

There are several characteristics that are used to determine if a larva specimen is an Oriental fruit moth. If a quick examination shows that the larva has alternating light dark bands, it is most likely a peach twig borer. But very young large don’t show the colors readily. Further examination under magnification looking for the presence of a structure called an “anal comb” located at the posterior end will usually allow for differentiation.  OFM lavae have 5 “teeth” in the comb whereas  the peach twig borer has 4 teeth. A codling moth larva can easily be ruled out because it completely lacks this structure. An additional structure that is often used to verify identity is the arrangement of the “crochets,” rings of hair-like structures anterior to the anal comb. PTB crochets are divided into two groups, whereas OFM crochets are in a single group. The above mentioned morphological characteristic are the easiest to look at if a quick ID is needed. But in some cases a more thorough examination of other traits may be required. See the gallery below for images used in identification of larvae.
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Adults

The adult OFM is a mottled grayish brown color with black flecking. Their overall color will darken if they have been stuck in a pheromone traps for some time. They are about 6-7 mm (@ 1/4 in) long and hold their wings to the side when resting. At a quick glance, OFM may seem similar in appearance to codling moth (CM). They are both generally grayish and hold their wings similarly at rest. But that’s where the similarity ends. CM are larger (9.5 mm or 3/8 in) and their color is more of a silvery-bronze with shiny brown scales towards the end of the forewings. Peach twig borer (PTB) adult moths look very different. They are slightly longer (8-10 mm or 0.3-0.4 in), have long narrow mottled slivery fringed forewings and light sliver heavily fringed hindwings, and have a structure on the head giving the appearance of a snout. PTB moths would never be confused for OFM or CM adults. See gallery below of similar adult moths.
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Comparison of Associated Moth Larvae

There are four major larval pests associated with stone fruit in the US. Here they are listed in order by increasing size.

Lesser Appleworm (Grapholita prunivora Walsh) (0.82 mm)
LAW is not reported in peaches, apricots or nectarines.

Cherry Fruitworm (Grapholita packardi Zeller) (0.89 mm)
CFW has only peach reported as possible host.

Oriental Fruit Moth (Grapholita molesta Busck) (1.11 mm)
OFM is found in stone fruit, but is rare in apples in Washington state.

Codling Moth (Cydia pomonella Linnaeus) (1.65 mm)
CM has no anal comb (as mentioned above) and is rare in stone fruits.

Acknowledgements

Content for this webpage was based on a joint WSDA & WSU training presentation for stone fruit cutter certification. Many of the images used in that presentation came from USDA/ARS, UC-IPM and the Clemson insect image galleries and Bugwood.org made public for educational purposes. Please do not copy or redistribute the images without their permission.

Image Credits (by order of appearance)

  • Early season adult OFM: Jack Kelly Clark, UC-IPM Program
  • OFM life cycle drawing: Art Cushman, USDA Systematics Entomology Lab; Bugwood.org
  • Exposed larva in hibernuculum: Cornell Cooperative Extension (NY State Ag. Experiment Station)
  • Early season 1st instar larva attacking stem: R. Coutin, INRA
  • Early instar larva attacking fruit surface: Jack Kelly Clark, UC-IPM Program
  • Late instar larva inside peach: Clemson Univ., USDA Cooperative Extension Slide Series; Bugwood.org
  • Late instar larva prior to pupation: G. Morvan, INRA, Montfavet; Bugwood.org
  • OFM pupa: Oregon State University
  • Shoot tip die-back with flagging: Jonas Janner Hamann, Univ. Fed. de Santa Maria; Bugwood.org
  • Early damage shoot wilt: Cornell Cooperative Extension (NY State Ag. Experiment Station)
  • Stem die-back: Clemson Univ., USDA Cooperative Extension Slide Series; Bugwood.org
  • Shoot die-back with dead ‘flagging’ leaves: OMFRA Crop IPM
  • Gummy ooze from exit hole: Clemson Univ., USDA Cooperative Extension Slide Series; Bugwood.org
  • Dead twig with exposed internal damage: Jonas Janner Hamann, Univ. Fed. de Santa Maria; Bugwood.org
  • Exposed larva feeding inside stem: H. Audemard, INRA, Montfavet, Bugwood.org
  • Black gummy deposits from surface feeding: Jack Kelly Clark, UC-IPM Program
  • Type 1 internal fruit damage (visible entry): Jack Kelly Clark, UC-IPM Program
  • Type 2 internal fruit damage (invisible stem entry): Cornell Cooperative Extension (NY State Ag. Experiment Station)
  • PTB feeding on peach: Jack Kelly Clark, UC-IPM Program
  • OBLR feeding on peach: Michigan State University Cooperative Extension
  • Leafroller feeding damage on peach surface: Utah State University Cooperative Extension
  • Codling moth feeding damage on peach: Shawn Steffans, Utah State University Cooperative Extension
  • Green peach aphid feeding damage on peach: Utah State University Cooperative Extension
  • Thrips damage on nectarine: Utah State University Cooperative Extension
  • Size comparison of similar larvae: Art Cushman, USDA Systematics Entomology Lab; Bugwood.org