Richard L. Miller
Julie A. Steele
Alan W. Smith
The apple maggot, Rhagoletis pomonella (Walsh), is a native insect widely distributed from North Dakota to Oklahoma and eastward. It is a major pest of homegrown apples in Ohio and, occasionally, is damaging in commercial orchards when certain insecticides are omitted. Hawthorn, plum, pear, crab apple, and cherry may serve as alternate hosts.
The adult fly is a little more than 6 mm in length, dark brown, with light and dark markings on the wings. The larvae are white, tapered maggots. Female flies lay eggs just under the skin of the apple. The larvae, or maggots, which hatch from the eggs, tunnel at random throughout the flesh of the fruit, usually avoiding the core. External signs of maggot infestation are the minute brownish egg punctures in the skin. These are often small, distorted or pitted areas on the surface of the apple, and sometimes a white wax covers the puncture. In early-maturing apple varieties, small tunnels occur throughout the flesh and under the skin through which the trails of the larvae may be visible.
Rapid decay and browning along the trails in infested fruit occur as the maggots feed. In late-maturing apples, there are less distinct external signs of infestation, but the flesh may contain small corky spots and discolored trails or streaks.
In Ohio, the apple maggot overwinters as a pupa in the soil. Adult flies begin emerging from their pupae in late June, continuing for a month or more. The peak emergence occurs from late July to early August, but some adults emerge in September.
When flies emerge, they usually spend about 10 to 14 days flying from tree to tree. During this period, the adults mate and females feed by lapping up moisture from the surface of leaves and fruits. Then they begin laying eggs.
The female has a needle-sharp egg-laying structure (ovipositor) at the tip of her abdomen that enables her to puncture the skin of the fruit. Each female is capable of depositing an average of 200 eggs. Eggs hatch in a few days, and the small, legless, white maggots immediately start to burrow through the flesh of the fruit. This burrowing often causes premature dropping of the fruit. Infested fruits have very little (if any) market value.
The maggots feed by tearing open cells in the apple flesh with a pair of black mouth hooks. They then absorb the cell juices. If the fruit is near maturity, growth is rapid and the larvae become fully grown and leave the fruit in 8 to 12 days. However, if eggs are laid in firm, immature fruit or in winter apple varieties, growth is much slower and many maggots may die due to the hardness of the fruit. If apples fall to the ground, the number of surviving larvae is larger.
The maggot leaves through a small opening made in the side of the fruit and enters the soil. Maggots usually settle in the top 1 to 3 inches of soil. The maggot transforms into a brown, hard, oval puparium within which the true pupa is formed. Some of the first brood pupae transform to adults and emerge in late August and September. However, the majority remain in the soil through two winters before appearing as adult flies.
|Puparium and Larva|
Few maggots leave the fruits while they are still hanging on the trees. Usually a few days elapse between the time an apple maggot-infested apple falls to the ground and the maggots leave it.
Dropped fruits of early varieties should be collected two to three times a week and those of later varieties at least once a week. Collected fruits should be put in a tightly sealed plastic bag and placed in a garbage can. In addition, the removal of hawthorn or other alternate hosts in the vicinity is a good practice.
As mentioned, maggots leave the fruit that has fallen to the ground, burrow into the soil and change to the pupa stage. Therefore, an insecticide applied to the ground around the trees should aid in killing apple maggots. The timing of the application must be around July 1-15.
Newly emerged female flies feed for a short time before they deposit their eggs. The flies obtain moisture by lapping up water droplets that collect on the fruits and leaves.
You can take advantage of this feeding habit to eliminate the females before they lay eggs. If you can apply an insecticide spray to the trees, at the right time, the flies will be killed as they feed on the toxic water and before they can harm the fruit. Spraying is the most reliable method of reducing maggot injury to apples. The use of an all-purpose fruit spray mixture plus the insecticides phosmet (Imidan) or carbaryl (Sevin 50 WP) should produce a spray that will adequately control the flies. Sprays for maggots should be applied in late June, mid-July, late July, and again in mid-August.
For more detailed information on apple maggot and other fruit pests, obtain a copy of Bulletin L-1, "Backyard Fruit Sprays for Insects and Diseases," or Bulletin #506A, entitled "Commercial Tree Fruit Spray Guide," from your county Extension agent.
When using an insecticide on edible fruits, a period of time must be observed when no spray is applied to prevent excessive residues of the insecticide on the harvested fruit. Examine your pesticide label to determine these day limitations.
NOTE: Disclaimer - This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registrations, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868