Fruit IPM Fact Sheet Fruit IPM Fact Sheet
APPLE MAGGOT
Scientific Name —
Rhagoletis pomonella (Walsh)
Reference:
Common Tree Fruit Pests
Angus Howitt, 1993. NCR 63, Michigan State University
As early as 1965, apple maggots seriously damaged the apple crop of New England. The apple maggot is a native pest that fed on the fruit of hawthorn and juneberries. On apples, this pest was known as "railroad worm." Host Range Apple maggots infest apples, pears, plums, apricots, hawthorns and crabapples. They are a major problem in the midwestern and eastern United States and eastern Canada. The apple maggot is also found in California, Oregon and Washington. Blueberry maggot is a similar species infesting blueberries in Michigan. Life Stages
Egg:
The eggs are 0.90 mm long and 0.25 mm wide, elliptical, semi-opaque and creamy white.
Larva: When full
grown, larvae are 8 mm long and 2 mm wide. They are usually cream-colored. The exact color
depends on the contents of the alimentary tact, which may have a greenish to brownish
tinge. The larva is a footless maggot. The head end can be distinguished by its pointed
shape and the presence of the dark, hook-shaped, chitinous jaws that dig the tunnels and
soften the pulp about the larva.
Pupa:
The pupa is pale yellowish brown and oval shaped. It measures about 4.5 mm long and is about half as broad.Adult: The female fly is about 5.8 mm long with a wing expanse of 12 mm. The thorax is black and marked with a dorsal white spot. The wings are broad and clear at the base. Four dark cross-bands traverse each wing. The abdomen of the female is black and striped with four white transverse bands. The ovipositor is sharply pointed and somewhat curved at the end; the tip of the abdomen is rounded. The male is smaller than the female. The male’s abdomen has only three white bands on it.
Factors Affecting Abundance
The maggot will build up large populations in unsprayed orchards. Life History The apple maggot passes the winter in the pupal stage in the top 2 or 3 inches of soil. In the summer, these pupae give rise to files, which emerge from the soil from late June through early September.
The flies do not begin to lay eggs until eight to 10 days after
emergence. During this period, called the preoviposition period, both the males and the
females rest and feed in the general area in which they emerge. They move readily from
tree to tree but normally only for short distances, usually no more than 200 or 300 yards.
The flies are not particularly attracted to apple fruits during this period and may be
found in unfruited trees and shrubs in and around the orchard.
At the end of the preoviposition period and after mating, the female flies seek out the fruits. They place the eggs just under the skin through a puncture made by the sharp, needlelike ovipositor. Females may lay eggs over an extended period of time. Eggs usually hatch in less than a week. Maggots hatching from these eggs tunnel through the apple, causing a breakdown and discoloration of the pulp. The mature maggots leave the fruit and enter the soil, where they transform to the pupal stage.
Most pupae remain in the soil until the following summer. A few individuals do not emerge until the second season; i.e., they remain in the pupal stage during the first winter, all the next season and the following winter. They emerge at the normal time during the second summer. These are not of much significance to growers who maintain good control every year, but they might be of importance in an orchard where the pest was allowed to become very numerous. Even after a vigorous and successful control program had been carried out for one year, there would still be some carryover for the second year.
Injury or Damage:
The apple maggot causes two forms of injury. The flesh surrounding a puncture where eggs are deposited in immature fruit often fails to grow with the rest of the apple and becomes a sunken, dimplelike spot in the surface. When the larvae feed and move through the fruit, they leave a characteristic brown trail through the flesh of the apple that can readily be seen when the fruit is cut open. When several maggots are in a fruit, the interior tissues may break down and depressions and discoloration may be visible from the outside. Injured apples usually drop prematurely.
Monitoring Use canary-yellow, sticky baited traps and red spheres coated with bird Tanglefoot to detect adult emergence. Growers can enhance the attractiveness of traps by sprinkling one or two teaspoons of fresh ammonium acetate over each trap when it is hung.
Place four yellow traps per orchard at about eye level in the foliage on the south side of trees one to two rows in from the edge of the orchard. Change the traps every three weeks until the end of July. Then replace the yellow traps with red spheres (with volatiles available) to detect female egg-laying activity. Clean and renew the Tanglefoot every two weeks.
Using 50 degrees F as a base, degree-days (DD) for apple maggot activity* are:| 900 DD | first adult emergence |
| 1,100 DD | first eggs laid |
| 1,600 DD | peak adult emergence |
| 1,750 DD | peak egg laying |
| 2,800 DD | end of adult emergence |
| *Data from MSU PETE model | |
Control
See the article on apple maggot monitoring and control in the June 28, 2005 Fruit CAT Alert.At present, no practical method of treating soil to destroy this stage has been devised, although in the past, when persistent pesticides such as the cyclodienes were employed as fruit sprays, the soil in the drip areas of trees contained high levels of these insecticides from the spray fallout. These residual pesticides in the soil were lethal to larvae leaving the fruit to pupate in the soil and greatly reduced resident populations of the pest in orchards.
Successful apple maggot control by killing the flies before egg deposition is possible and practical because of the 8- to 10-day preoviposition period. This usually allows sufficient time to kill the flies before they can infest the fruit. Theoretically, a toxic spray need not be applied until eight days after the first emergence and not again until eight days after the residual action of the spray is gone. In practice, however, a material with 10 days’ residual activity must be applied at 10-day spray intervals to ensure good control. Practically, then, it is necessary to maintain a toxic residue in the orchard during most of the period of fly emergence. Adding liquid protein hydrolysate (available commercially) to the spray can greatly enhance the spray’s effectiveness, because the fly actively feeds on and ingests the mixture of spray with the liquid bait. This can help compensate for inadequate coverage and reduced pesticide dosages.
Because flies move about freely in vegetation around the apple trees, particularly during the preoviposition period, it is desirable to spray interplanted and adjacent trees and shrubs. This free movement makes maggot control in backyard plantings very difficult.
Apple maggots are rarely residents of commercial orchards—they normally fly into commercial orchards from abandoned or neglected orchards. When flies enter commercial orchards varies greatly from orchard to orchard and from season to season. Monitoring will detect the first entry of flies into a commercial orchard. With careful monitoring, growers can control apple maggots with a minimum number of sprays. Studies conducted by entomologists have demonstrated that entry into an orchard by adult flies may vary from early July until mid-August. Traps should be set in the periphery of commercial orchards in locations where flies are most likely to enter. In many cases, it may be necessary to treat only the first several rows on the periphery, where flies enter the orchard. If at any time during monitoring an average of five flies per trap are caught in a week, apply an insecticide immediately. Flies caught for one to four days following the insecticide spray can be discounted.
