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Ministry of Agriculture, Food and Rural Affairs

Apple maggot

Adult apple maggot flies – male on left, female on right. (Dr. Rob Smith, retired, Agriculture and Agri-Food Canada, Kentville) Apple maggot sting Apple maggot tunnels Yellow board
Click to enlarge.

Beginner

Scientific Name
Rhagoletis pomonella (Walsh)

Identification
Eggs:

  • 0.9 mm long.
  • Elliptical.
  • Semi-opaque and white.

Larvae:

  • Four larval instars.
  • Mature larvae:
    • White to pale cream in colour.
    • Legless and tapered,
    • Reaching approximately 6.5-8.0 mm in length and 1.5-2.0 mm in width.
    • Careful examination under a microscope reveals two dark mouth hooks at one end.

Pupae:

  • 4.5 mm long.
  • Light brown and oval shaped.

Adult flies:

  • 5-6 mm in length (slightly smaller than a house fly).
  • Shiny black with a white dot on its thorax.
  • Dark banding pattern on each wing in a characteristic “F” design.
  • Female fly is slightly larger than the male, has four white pale lines on the abdomen and a squared-off or tapered posterior end.
  • Male has only three white lines and a rounded abdomen. 

Damage:

  • Oviposition stings on the fruit surface resemble a small pinprick, darkening over time and appearing pitted or dimpled.
  • Larval feeding tunnels in fruit cause breakdown and discolouration of the pulp.

Often Confused With

  • Cherry fruit fly- Apple maggot adults are distinguished from other related flies by the dark banding pattern on each wing.

Period of Activity
Apple maggots adults begin migrating into orchards from early July through harvest. Apple maggot activity usually peaks in commercial orchards in August.

Scouting Notes
Apple maggots are a pest in most apple growing areas of Ontario, although in some areas, like Essex-Kent, the pressure seems to be reduced due to a lack of wild hosts. For monitoring apple maggot adults, place a minimum of five sets of traps each including one yellow sticky boards with a bait, in trees along the edge of the orchard, adjacent to woodlots or other large sources of alternative hosts. Apple volatiles lures are more attractive and selective than protein lures, and their use is recommended. Place traps at eye level facing out from the orchard, with 60-100 m between traps. Remove any foliage within 30-50 cm of traps to enhance visibility to flies. Set up additional traps within the orchard in blocks with a history of damage and/or resident populations.

Place trap sets in orchard by mid to late June and monitor twice weekly. Clean traps frequently by scraping off insects and re-coating with Tangletrap or replace. Replace volatile lures according to the manufacturer’s directions.

Thresholds
Apply insecticides 7-10 days after the first fly is captures on a yellow board or immediately after the first female is captured on red spheres. Re-apply subsequent sprays every 7-21 days depending on the residual activity of the product used, weather (precipitation) and where monitoring indicates continual apple maggot flight.

Advanced

Scientific Name
Rhagoletis pomonella (Walsh)

Identification
Eggs are 0.9 mm long, elliptical, semi-opaque and white. There are four larval instars. Mature larvae are white to pale cream in colour, legless and tapered, reaching approximately 6.5-8.0 mm in length and 1.5-2.0 mm in width. Careful examination under a microscope reveals two dark mouth hooks at one end. The pupa is 4.5 mm long, light brown and oval shaped. The adult fly is 5-6 mm in length (slightly smaller than a house fly), shiny black with a white dot on its thorax. Apple maggot adults are distinguished from other related flies – that occasionally appear in the orchard and may appear on baited traps – by the dark banding pattern on each wing. The characteristic “F” design of this banding is a diagnostic feature of apple maggot. The female fly is slightly larger than the male, has four white pale lines on the abdomen and a squared-off or tapered posterior end. The male has only three white lines and a rounded abdomen. 

Apple maggots damage fruit in two ways: 

  • oviposition stings on the fruit surface;
  • larval feeding tunnels in fruit cause breakdown and discolouration of the pulp.

Oviposition stings are difficult to detect initially. They resemble a small pinprick, darkening over time and appearing pitted or dimpled. Feeding and tunneling of larvae inside the fruit is often called “railroading”. As larvae grow, tunnels become larger and begin to discolour. Invasion by disease fungi, Alternaria spp. and Pseudomonas spp. leads to further decay. Heavily infested fruit becomes completely rotten. Early-maturing varieties are often most severely infested.

Apple maggot populations are high in wild apple trees and abandoned apple plantings throughout Eastern Canada and the United States, and approximately 80% to 100% of fruit in untreated areas can become infested.

Often Confused With

  • Cherry fruit fly- Apple maggot adults are distinguished from other related flies by the dark banding pattern on each wing.

Biology
The apple maggot over-winters as a pupa in soil. Adults emerge from late June through September, with peak flight into commercial orchards in August. Emergence is closely linked to soil moisture levels – in dry years, some pupae remain in soil until the following growing season.

Apple maggot flies are strong fliers. Field studies indicate they fly up to 3 km from alternative hosts or unmanaged areas. Male flies generally begin emerging before the females, but by peak emergence the sex ratio is about 1 to 1. Both sexes initially feed on sugar sources such as nectar and honeydew, as well as protein sources such as bird faeces, before becoming sexually mature 7-10 days after emergence. Mated females are attracted to shape, colour and odours associated with ripening host fruit. 

Each female will produce 300-400 eggs, laid over a period of three to four weeks. The female punctures the apple skin with her ovipositor and lays an egg into the developing fruit. When a female deposits her egg, she also marks the apple with a pheromone to deter others from ovipositing in the same fruit. Eggs hatch after three to seven days and the larvae burrow into the fruit where they feed on the pulp. Development of larvae is slower within green fruit. After three to four weeks of feeding, heavily infested apples fall to the ground and rapidly decompose. The breakdown of fruit tissues allows the larvae to complete their development, and survival of maggots is low where apples remain on the tree. 

Mature larvae exit the apple, tunnel into the soil to a depth of 2-5 cm, pupate and enter diapause (resting state). The pupae remain in soil for more than one year if environmental conditions (moisture and temperature) are not favourable for emergence. Apples with only one or two stings often remain on the tree until harvest. Apple maggots usually have a single generation each year in Ontario. They are active until the first hard frost. A partial second generation occurs in some years when early maturing apple cultivars are attacked and weather conditions are favourable for rapid development.

Period of Activity
Apple maggot adults migrate into orchards from early July through harvest. Apple maggot activity usually peaks in commercial orchards in August.

Scouting Notes
Apple maggots are a pest in most apple growing areas of Ontario, although in some areas, like Essex-Kent, the pressure seems to be reduced due to a lack of wild hosts. Traps developed for monitoring apple maggot adults, use the insect’s response to visual and olfactory cues to track adult activity in the field. These include various combinations of yellow sticky boards, sticky red spheres, and lures containing ammonium, fruit volatiles (butyl hexanoate) or other compounds.

Sexually immature males and females are attracted to the yellow boards, which mimic nectar sources at a time when adults are actively seeking carbohydrate sources. Sexually mature females ready to lay their eggs are attracted to red spheres, which mimic ripe apples. The addition of commercially available fruit volatile lures or vials containing ammonium acetate enhance traps captures.

For monitoring apple maggot, place a minimum of five sets of traps each including one yellow sticky boards with a bait, or one yellow stick board and two baited red spheres, in trees along the edge of the orchard, adjacent to woodlots or other large sources of alternative hosts. Apple volatiles lures are more attractive and selective than protein lures, and their use is recommended. Place traps at eye level facing out from the orchard, with 60-100 m between traps. Remove any foliage within 30-50 cm of traps to enhance visibility to flies. Set up additional traps within the orchard in blocks with a history of damage and/or resident populations.

Place trap sets in orchard by mid to late June and monitor twice weekly. Clean traps frequently by scraping off insects and re-coating with Tangletrap or replace. Replace volatile lures according to the manufacturer’s directions.

Thresholds
Apply insecticides 7-10 days after the first fly is captures on a yellow board or immediately after the first female is captured on red spheres. Re-apply subsequent sprays every 7-21 days depending on the residual activity of the product used, weather (precipitation) and where monitoring indicates continual apple maggot flight.

Management Notes

  • The removal of alternative hosts including hawthorn or wild apple within 100 m of the orchard reduces pressure from migrating flies. Sanitation measures include removal and disposal (destruction, burial) of culled fruit.
  • Insecticides to manage apple maggots vary in the life stage of the insect targeted and mode of action.
  • Apply insecticides such as the neonicotinoids and organophosphates 7-10 days after the first fly is captured on a yellow board or immediately after the first female is captured on red spheres.
  • Apply products formulated with attractive baits, such as naturalytes, immediately after the first fly is captured on yellow sticky cards.
  • Apply products that provide a protective barrier (kaolin clay) between the plant and pest before adult flight begins.
  • Re-apply subsequent sprays every 7-21 days depending on the residual activity of the product used, weather (precipitation) and where monitoring indicates continual apple maggot flight.
  • See OMAFRA Publication 360, Guide to Fruit Production - Chapter 3 Apples (PDF) or Apple Calendar only (PDF) :
  • Keep in mind that even if timing of apple maggot sprays correlates with those for codling moth, not all products are effective for both pests. 
  • Border or perimeter sprays reduce pest populations and minimize negative effects of pesticides on the environment.  Border sprays refer to pesticide applications applied to the outer 20 m of orchard perimeter. In commercial orchards without resident populations, this distance is sufficient to intercept apple maggot flies from penetrating the orchard. The efficacy of border sprays using new chemistries (neonicotinoids, naturalytes and particle films) is not yet established, and border sprays using products with these chemistries are not recommended at this time. If damage is detected during routine monitoring of the orchard, replace a border spray program with a cover spray program. Border sprays are effective only when the following conditions are met:
    • orchards are larger than 4 ha
    • orchards are square or rectangular, not irregularly shaped
    • there is no history of apple maggot or codling moth infestations within the orchard and as determined by monitoring in the current season
    • the orchard is not directly adjacent to any abandoned orchard or under heavy pressure from nearby wild hosts
    • adequate coverage over the 20 m deep orchard perimeter is attainable (dependent on factors such as canopy density and spray drop size and velocity)
    • orchards should be well-maintained (e.g. regular annual pruning, balanced fertilizer program
  • At the headlands, turn off nozzles on one side of the sprayer and blow the spray into the orchard while traveling along the outer edge.
  • To eliminate any live larvae in harvested apples, a cold storage period of eight weeks at temperature below 5°C is effective in killing them. This practice may satisfy the export restriction of some countries.