Blueberry Maggot in Ontario

Introduction

The blueberry maggot (Rhagoletis mendax) is a regulated pest in Canada. The Federal Plant Protection Act and Regulations place movement restrictions on blueberry fruit, plants, soil and containers from areas known to be infested with blueberry maggot. These laws are in place to prevent the spread of this pest from infested areas (i.e. Nova Scotia, New Brunswick, Prince Edward Island, Maine, New York, Michigan) to non-infested areas (i.e. parts of Ontario, Quebec, British Columbia).

This insect is native to eastern North America, including Nova Scotia, New Brunswick, Prince Edward Island and the eastern U.S. The blueberry maggot was discovered for the first time in the provinces of Ontario in 1993 and Quebec in 1996. In Ontario and Quebec, the blueberry maggot is limited in distribution, and extensive surveys have been conducted to delimit the infested areas. In Ontario at the present time Wainfleet Township and Charlotteville Township are regulated for blueberry maggot. There are also three isolated quarantine sites in the province.

Whole municipalities in Quebec or Ontario are regulated if they contain at least one infested natural (wild) site or an infested grower site with host plants within 500 metres of the infested site. Note: An infested grower site which is isolated (no other host plants within 500 metres) means that the grower site is a regulated area, but not the whole municipality). Maps of infested areas can be found on the Canadian Food Inspection Agency website.

If blueberry maggot becomes an established pest in Ontario, blueberry production costs will increase and export markets may be affected.

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Identification

The adult blueberry maggot is a black and grey fly, slightly smaller than a housefly (5 mm long), with a white spot on its back. It has one pair of wings marked with distinct black banding. The adult blueberry maggot is identical in appearance to the apple maggot. Both belong to the same genus, however, from an ecological standpoint, the two forms are distinct and independent. Blueberry maggot does not infest apple and vice versa. These two pests can only be distinguished by microscopic examination of the female's ovipositor.

Figure 1. Wing patterns of Blueberry Maggot adult and related species.

The blueberry maggot larvae, or maggots, are found inside infested blueberry fruits. The larvae are colourless at first, later becoming white, and are up to 8 mm long. They have no legs and no distinct head.

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Life Cycle

There is one generation per year. The blueberry maggot overwinters as a pupa, buried 2 - 5 cm in the soil beneath infested blueberry bushes. The pupa is brown or yellowish-brown, barrel-shaped and about 6 mm long. Adult flies emerge from these pupae beginning about mid-June and continuing throughout the summer. Emergence is affected by many factors, including soil temperature, soil moisture, depth of the pupae in the soil, and the amount of chilling received during the winter months. A small portion of the pupae may lie dormant for more than one year, especially if they do not experience a sufficient cooling period during the first winter.

Adult blueberry maggot females begin to lay eggs about 7 - 10 days after they emerge. Eggs are usually inserted just beneath the skin of ripe or ripening blueberry fruit. The eggs hatch in 2 - 10 days. Larvae tunnel throughout the fruit, feeding on and liquefying the fruit as it matures. Infested fruit are very difficult to detect until the fruit is broken or cut open to reveal the larvae. Very small larvae are almost colourless, and only larger larvae are readily visible. Fruit in late stages of infestation may be softer, or appear to ripen early. After about 20 days inside the fruit, the larvae exit the fruit, drop to the ground and pupate. At this point, infested fruit may also have fallen to the ground.

Figure 2. Top view of blueberry maggot adult.

Figure 3. Egg-laying scar on blueberry (greatly magnified).

Figure 4. Larvae causing damage to blueberry.

Figure 5. Blueberry maggot larva.

Figure 6. Blueberry maggot pupa.

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Artificial spread of the blueberry maggot may occur if blueberry plants are transported with live pupae in the soil surrounding the roots, or if fruit or debris infested with mature larvae or pupae is discarded on or near a blueberry production field.

Alternate Hosts

Blueberry maggot is known to infest lowbush blueberry, small cranberry, highbush blueberry, lingonberry and huckleberry. Transportation of all rooted plants of these species is regulated by Agriculture and Agri-food Canada. Bunchberry was once implicated as a major host. Dwarf serviceberry and wintergreen are possible hosts.

Monitoring

Adults

Activity of adult blueberry maggots can be monitored using sticky yellow traps, baited with ammonium acetate. These traps, also used for apple maggot, are available from a number of suppliers (see Appendix 1).

Traps should be placed by mid-June on the perimeter of commercial fields, or just outside of commercial fields in abandoned or wild blueberries, if these are nearby. Be sure the traps are visible by hanging them from outer branches, 4 - 6 feet from the ground, and by removing twigs and foliage in the vicinity of the trap. If blueberry plants are small, hang the traps from stakes above the plant. Place 2 - 3 traps per field, or 1 - 2 traps per hectare. The traps will catch a wide assortment of flies and other insects. Check for blueberry maggot flies by examining the wing patterns of the trapped insects. If no blueberry maggots are trapped, remove all dead flies and debris, replacing the trap when necessary. If blueberry maggots are suspected on the trap, do not attempt to remove the insect from the trap. Rather, remove the whole trap and place it in a cool, dry place. Contact the Canadian Food Inspection Agency (CFIA) for assistance in identification of the trapped insect (List of CFIA area and Regional Offices).

Larvae

Monitoring for blueberry maggot larvae is difficult, as infested berries are nearly impossible to detect until the infestation is quite advanced and the larvae are nearly mature. Investigate customer complaints carefully. Infested fruit is most likely to become evident when fruit is processed by canning or cooking. The peak times for blueberry maggot larvae in fruit will be between mid-July and mid-August. Samples of fruit can be inspected for larvae by using the water test, or the brown sugar test. These tests are outlined in Appendix 2.

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All photos courtesy of Agriculture and Agri-food Canada.

Related Links

• Publication #360, Fruit Production Recommendations
  
• Rhagoletis mendax Curran Blueberry Maggot, Canadian Food Inspection Agency, Plant Pest Information
  
• Phytosanitary Requirements For The Importation From The Continental United States and For Domestic Movement of Commodities Regulated for Blueberry Maggot D-02-04
• Blueberry maggot infested areas
• Map of infested areas in Ontario
• List of CFIA area and Regional Offices
• Pest Monitoring Equipment Suppliers