Arthropod Damage


The Arthropod section of the card set includes all the major insect damage found in Washington apples. This section also includes some mite damage. The upcoming revision of the Defects & Disorders Guide may include additional forms of damage, such as bird pecks and rodent feeding, as well as, any emerging or reclassified disorders. To navigate directly to the pest damage of interest use the links below this text block.  The card images shown on this site are slightly modified from their original form to accommodate web formatting. Any reproduction of the card images or content without permission is in violation of WSU Copyright policies.

Codling moth    Leafrollers     Other caterpillars    True bugs    Aphid & mealybugs     Scale, thrips & others

Codling moth

Codling moth (Cydia pomonella; CM) has become a serious quarantine pest for exporting apples. Some countries, such as Taiwan and China, require additional sampling to ensure that fruit are codling moth free prior to packing.

calyx end of apple showing wormhole.
Figure 1. Calyx end of apple showing “wormhole.” The residual blossom can hide holes making it easy to miss.
Figure 2. “Wormholes” can also be found in the stem bowl. This area should also be checked carefully.
Figure 3. “Stings” are early or unsuccessful entries defined as being under ⅛ inch deep; ⅛ inch or deeper is considered a “wormhole.”
Figure 4. “Wormholes” are tunnels into the fruit made by feeding larvae.
Figure 5. CM larvae tunnel into the fruit to feed on the seeds at the core before exiting through the same or a new tunnel.
Figure 6. To check for internal larvae the fruit must be cut vertically from stem to calyx through the core. Fungal or bacterial growth are common side effects.


Two species of leafroller (LR) are common to the Pacific Northwest: Obliquebanded LR (Choristoneura rosaceana; OBLR) and Pandemis (Pandemis pyrusana). Both feed primarily on foliage, but fruit damage can occur when the foliage touches the fruit.

Figure 1. Sever early season feeding can cause distortions of the fruit shape along with the feeding scars.
Figure 2. Early season feeding scars can appear lattice-like.
Figure 3. Late season feeding by Pandemis produces shallow, discontinuous surface scars or holes, often resembling codling moth stings.
Figure 4. Late-season feeding by OBLR may be deeper and more continuous than Pandemis injury.
Figure 5. Severe summer feeding damage. Webbing my be present in hole. Can look like codling moth holes without frass, but does not extend into the seed core.

Other caterpillars

Cutworm” is a general term referring to noctuid caterpillars, such as fruitworms, cutworms, and armyworms. Normally they feed on weed hosts, but they may move freely between weeds and apple trees. Severe fruit damage can occur while they feed on leaves that are close to apples.

Figure 1. Surface feeding with decay.
Figure 2. Deep narrow, scarred “bowl” made by a fruitworm.
Figure 3. Cutworm surface feeding causing a scarred “bowl.”
Figure 4. Frequently, cutworms stay at one spot, making a shallow bowl. When they leave, the hole scars and may crack over time.

True bugs

There are three major Hemiptera (family of true bugs) that may cause feeding damage on apples: Lygus (Tarnished plant bug), stink bugs and Campylomma (Mullein plant bug).

Figure 1. Lygus damage is caused by feeding on flower parts or young fruit. Feeding kills cells preventing growth in the surrounding area. The resulting fruit is deformed with a deep pit sometimes called cat-facing.
Figure 2. Stink bug feeding resembles bitter pit. This figure compares stink bug damage (left) to bitter pit (right). Stink bug feeding damage is more conical in shape, lighter in color, and less corky than bitter pit.
Figure 3. Stink bug usually feed on the top half of the fruit. Bitter pit usually is more towards the bottom portion.

Figure 4. Campylomma feeds on mites and aphids. However, early in the season they may feed on flowers and developing fruit. Early in the season feeding damage appears as one or more dark, raised, corky warts inside a shallow depression (top right). As the fruit grows damage appears as small dark raised spots (bottom right).

Aphid & mealybugs

Aphids and mealybugs are closely related insects. Normally, they infest the vegetative parts of the tree. However, with a heavy infestation, the insects move on to the fruit from the stem, or they may crawl over from leaves touching the fruit. Wooly apple aphid (WAA), Rosy apple aphid (RAA) and Grape mealybug are those most commonly found in the Pacific Northwest. Species identification is made by an entomologist or trained fieldman.

Figure 1. The insect may find its way inside the fruit. Shown here are two Wooly apple aphids, one smaller purplish nymph above the seed, and a wooly adult below and to the left.
Figure 2. Two Wooly apple aphid nymphs deep in the calyx. Aphids can enter the seed core this way.
Figure 3. Frequently, fruit infested with aphids or mealybugs have sticky honeydew, a by-product of feeding. Shown here are two mealybugs. The shiny areas on the fruit are from honeydew. Honeydew is a good growth medium for fungus, such as, sooty mold. Presence of sooty mold should alert you to the possibility that the fruit lot came from an infested orchard block.

Scale, Thrips, and other insects

There are several other insects that may only occasionally cause fruit damage. However, if present, they could cause quarantine problems at some export destinations.

Figure 1. Severe San Jose scale present with darker pigment rings around the feeding sites. Scale may be found only in the stem bowl or calyx if the infestation is light, or may cover the fruit when the infestation is heavy.
“Pansy spots” from thrips egg laying appears early as bleached tissue around a small dimple (top). Later may have a dark border around greenish depression (bottom). There may be one or more spots per fruit. Damage is isolated to the surface layers. Discovery of thrips could cause export lot rejection.
Figure 3. Areas with apple maggot are subject to strict quarantine regulations. External dimpling from egg laying and internal feeding are pictured here.
Figure 4. Blister mite is not common in apples. Feeding causes surface scaring after the mites are gone. Other mite feeding may cause russet similar to powdery mildew damage.