Apple maggot—Rhagoletis pomonella
The larval stage of apple maggot (family Tephritidae) feeds in the fruit of apple, hawthorn, and occasionally other Rosaceae. This pest is found in Northern California from Sonoma County northward. If found further south in California, please report findings to the local office of the County Agricultural Commissioner.
Identification
Adult apple maggots (flies) are about 1/5 inch long with a brown head and black abdomen and thorax. They have clear wings with black bands, an obvious white spot on the rear of the thorax, and pale cross bands on the abdomen. Females have four pale cross bands on the abdomen; males have three. Their body coloration and wing markings distinguish apple maggots from other Tephritidae that occur in California including olive fruit fly and walnut husk fly. Note that pomace or vinegar flies (drosophilids, family Drosophilidae) are also called fruit flies, but drosophilids are much smaller species.
Larvae of apple maggot occur in fruit and are cream colored and up to 1/4 inch long. They have a blunt posterior and taper toward the head where there are 2 black hooklike appendages.
The oblong puparium (pupal covering) is orange and about 1/5 inch long. Puparia are found mostly in topsoil.
Life cycle
Apple maggots develop through four life stages: egg, larva, pupa, and adult. Prepupae or pupae overwinter in the soil. Adults emerge from June through August with peak emergence in July. A portion of the pupae may remain in the soil and not emerge until the following year.
Newly emerged adults are sexually immature and must feed on honeydew produced by aphids, psyllids, soft scales, or other phloem-sucking insects before they are ready to mate. Mated adult females lay eggs under the skin of apples or fruit of other Rosaceae and then mark the fruit with a pheromone that discourages other apple maggot females from laying eggs in that fruit. Females lay about 300 eggs during their 30-day lifespan. Eggs hatch in about 2 to 10 days.
The hatching larvae feed on and tunnel in the flesh of the fruit and introduce fruit decay pathogens. Larvae feed for about 3 or 4 weeks and develop through 3 increasingly larger instars before pupating. The mature larvae (prepupae) emerge from the fruit and burrow into the soil where they pupate.
Apple maggot generally has one generation per year. Some years there may be a partial second generation.
Damage
In soft-fleshed apple varieties, a small, dark, decayed spot develops at the egg laying site. In hard-fleshed varieties, the egg laying site develops a dimple. Young larvae tunnel throughout the apple flesh, leaving brown, irregular trails. The tunnels enlarge as the larvae grow and fruit decays along the trails. Once fruit develops significant internal rot it drops. The maggot-infested and decayed fruit is unappetizing or unpalatable.
Solutions
Because this pest occurs only in Northern California, to prevent its spread it is illegal to move home-grown apples into some counties further south. Counties that prohibit the introduction of noncommercial apples (as of 2021) include Contra Costa, El Dorado, Fresno, Kern, Kings, Merced, San Benito, San Joaquin, San Luis Obispo, Stanislaus, Tulare, and Ventura. If suspected apple maggot adults or any maggots are found in apples in Central or Southern California, please report this to the local office of the County Agricultural Commissioner.
Sanitation helps to control apple maggot. Clean up and discard fallen fruit frequently to remove some immature flies that otherwise would contribute to next season's fruit infestation. Fruit on the tree can be regularly inspected and those showing brown feeding trails on their skin can be picked early and discarded.
Several sticky red sphere traps can be hung in each apple tree to reduce the abundance of adult female flies that otherwise would lay eggs. Note that if trees are regularly visited by birds or other wildlife, sticky traps pose an entanglement hazard and sticky trapping may be undesirable.
Bagging fruit to exclude codling moth will also control apple maggot. See Pest Notes: Codling Moth for discussion of fruit bagging.
Where apple maggot has been a problem during previous growing seasons and insecticide may be applied, place at least 2 yellow sticky traps in apple trees in early June and inspect them regularly for adult apple maggots. When the flies are first caught, they can be controlled by spraying trees with spinosad. Most effective is insecticide that is sold premixed with a fruit fly attractant, such as GF-120 NF Naturalyte Fruit Fly Bait. Alternatively, a fruit fly attractant (e.g., Nu-Lure Insect Bait) can be mixed with spinosad and sprayed. If adult flies continue to emerge, repeat application every 7 to 10 days may be warranted.
Adapted from Pest Management Guidelines: Apples, University of California Statewide Integrated Pest Management Program (UC IPM). |
