Apple Maggots

Apple maggots are a nasty surprise when biting into an apple.

Apple infested with maggots (Image from "Annual report of the New York State College of Agriculture at Cornell University and the Agricultural Experiment Station" 1911-1971) Public Domain

Native to Canada and the northeastern U.S., apple maggots (Rhagoletis pomonella) originally lived and fed on hawthorn trees and fruit. Apples were introduced to those regions in 1710, but no mention of apple maggots was made until 1860, when infestations became heavy. Apple maggots have slowly spread across the country, reaching Oregon in 1979. Four years later, 101 flies in 38 orchards were found in California apples. Today, apple maggots are found practically everywhere in North America, which the exception of a few valleys in British Columbia. Being responsible for millions of dollars of crop losses each year, apple maggot quarantines are in place in several California counties.

Identification

​Adult apple maggot flies are frequently mistaken for spiders, at first glance. Disturbed adults will turn their wings 90-degrees and move their body up and down while walking sideways. Why they don’t simply fly away, I’ll never know. Flies are less than 1/4” long, dark, with white stripes, a white dot on the middle segment (thorax), and yellow legs. The wings have black bands that look like a capital “F”. The head is yellowish and the eyes can be green or dark red. Larvae are white, legless, and 1/4” long, with two dark mouth hooks. The pupae are tan to dark brown hard cases found in the soil.

Female apple maggot fly (Joseph Berger, bugwood.org) CC BY 3.0

Apple maggot lifecycle

A female fly will lay up to 500 small, white eggs, each on a separate fruit, under the skin of apples, cherries, apricots, plums, pears, wild rose, Pyracantha, and crabapples. The maggots, or worms, will stay inside their host fruit, safely feeding until the fruit falls from the tree. The fattened larvae then burrow into the ground where they pupate in the soil over the winter. Adult flies emerge June through September and then feed on honeydew and bird poop. Yuck!

Apple maggot damage

You may see small dimples where eggs have been inserted under the skin of vulnerable fruits. From there, the larvae go unnoticed as they feed, until you take a bite. Then, brown tunnels and a (hopefully!) intact larvae can be seen. You can tell the difference between apple maggot and codling moth damage because codling moth larva prefer apple cores, while apple maggots prefer the fruit. Personally, I don’t want to see either one in my apple!

Apple maggot control

Apple maggots have many natural enemies, such as parasitic wasps, so broad spectrum pesticides should be avoided. Since the larvae are safe once inside the fruit, pesticides won’t work anyway. Instead, sticky traps can be used. These traps are usually a red sphere, like an apple, or a bright yellow panel. I”m not sure why so many insects are attracted to yellow paper, but it seems to be pretty common.

These are not pheromone traps, which can attract pests from several yards away. Instead, a protein-ammonia mix is used and it is only effective in the immediate area. These traps should be hung in the outer third of the tree canopy, in an open area. You may need to remove nearby foliage, up to 18 inches from the trap, to make it more visible (and alluring) to apple maggot flies. You can buy these traps at garden centers and they should be inspected every few days and replaced every 2 to 3 weeks, depending on how messy they get. The spheres should be cleaned and re-stickied every 4 weeks. If you catch any apple maggot flies in your traps, you really should contact your local County Extension Office or the Department of Agriculture. You can also participate in a fun civilian project called The Big Bug Hunt, which uses our inputs to create a warning system that alerts you when insect pests are headed your way. It’s pretty neat.

By monitoring where this pest is seen, the proper quarantines can be put in place to reduce the damage. If apple maggot flies are trapped, the traps should be kept in use until no more flies are trapped.

Protect your apple and other crops by monitoring for this relatively new pest.