ECONOMIC IMPORTANCE AND DAMAGE

The blueberry maggot has been reported from the following Canadian locations: Nova Scotia, Prince Edward Island, New Brunswick (except for Restigouche, Madawaska, Victoria and Carleton counties). A few very localized infestations have been reported from Ontario, northeast of Lake Erie, from 1993 to 1994 which may have now become eradicated. It is prohibited to ship fresh fruit from the maritime provinces to Newfoundland or British Columbia. Shipment of fresh fruit to all other noninfested areas in Canada and parts of the United States must be certified to be free of maggots.

The blueberry maggot is the most serious pest of lowbush blueberries. Although larvae damage fruit, the seriousness of this pest results from the presence of maggots in harvested fruit. The maggot is not harmful to health, however, its presence makes fresh, canned or frozen fruit unacceptable for markets. Damage is initiated by the female fly laying an egg under the skin of the berry. The developing maggot feeds within the berry destroying the pulp, causing the berry to become shriveled. The infested berry tends to drop off the plant prematurely. Infested berries that remain on the plant and are harvested can result in major losses as there is a zero tolerance for maggots in most fresh markets, and a low tolerance in processing markets. Consult with your buyer for particular requirements.

LIFE CYCLE AND DESCRIPTION

The blueberry maggot has four life stages: egg, maggot, pupa, adult fly. Adult emergence varies according to location and year. In New Brunswick, adult flies begin to emerge from the ground in the last week of June in the south and the first week of July in the north. Almost all the flies emerge over a period of thirty days. However, a few can be trapped until frost occurs. Adult flies develop for one to two weeks before egg-laying begins. At this time, the first blueberries start to ripen. The female will lay eggs for fifteen to twenty-five days. However, egg laying continues for thirty days as adults emerge over an extended period of time. The female may deposit up to 100 eggs. There is usually one egg per berry.

The small white egg hatches in seven to ten days into a maggot (the larval stage) (Figure 1) which feeds for two to three weeks. The full-grown maggot is 8 mm long, whitish in colour, and is pointed at one end and blunt at the other. In mid to late-August, maggots start to leave the infested berries and enter the soil to form pupae, usually 3 to 5 cm below the soil surface.

Pupae are oval, yellowish-brown in colour, and 3 to 4 mm long. Most pupae develop and emerge as adults the following year (typically the sprout year). Approximately 5 to 20 percent remain in the soil for two years and then develop into adults. Approximately one percent remain in the soil for three or four years.

The adult (Figure 2) is slightly smaller than the house fly and is 3 to 4.75 mm long. The body is dark brown, marked with grey and white. The female has four white stripes across the abdomen, while the male has three. The female has a needle-shaped egg-laying structure that can be extended out from the abdomen, or withdrawn. The abdomen of the male is slightly more rounded than that of the female. The wingspan is about 8 mm.

The blueberry maggot is identical in appearance to the apple maggot, species: Rhagoletis pomonella (Walsh). However, there are generally few apple trees nearby blueberry fields. The apple maggot will not infest blueberries. The blueberry maggot has a distinctive marking on its wings which distinguishes it from other similar species (Figure 3). The dark brown to almost black banding on the blueberry maggot wing is F-shaped with a continuous line at the base of the F pattern. The banding pattern is not continuous on the wing of black cherry fruit fly, species: Rhagoletis fausta (Osten Sacken).

The blueberry maggot attacks other types of berries found on blueberry land, including: huckleberry, shadbush (serviceberry), barrenberry, bunchberry, wintergreen, lingonberry. These weeds may increase infestation levels. Bunchberry may be more of a concern as it can produce fruit on newly pruned land.

PEST MANAGEMENT

Cultural Practices. The following cultural practices aid in controlling the blueberry maggot: pruning, sanitation, weed control. Pruning fields reduces pest levels as there is no crop available for emerging flies to deposit their eggs. This forces the blueberry maggot to fly elsewhere to lay eggs. Pruning practices are more effective in isolated fields that are not divided up into sprout and crop sections. Sanitation practices include: 1) Not leaving unpicked blueberries in infested fields. The field should be completely harvested to prevent reinfestations from unharvested strips or field sections. 2) Debris from winnowing piles should be removed and destroyed as it may contain many larvae. Weed control is important as weeds provide sheltered areas for the flies. Some weeds produce berries which serve as alternate hosts for blueberry maggot development.

Monitoring. Pherocon®¹ AM traps are used to monitor adult blueberry maggots. The trap is rectangular in shape. One side is yellow and sticky since the yellow colour attracts flies. Traps are also available with a protein-based bait. The trap is suspended, from a stake, in a V-shape with the yellow side pointed outward (Figure 4). The bottom of the trap should be 10 to 15 cm above the top of the blueberry plants. Traps should be placed at a rate of two per hectare, in areas where berries are present, preferably in sheltered areas away from the prevailing winds. Suitable locations include: nearby woods, bushes or rock piles. Traps should also be placed adjacent to sprout fields. In fields larger than 10 hectares, traps should be placed every 100 metres, near the edge of the field. The traps should be placed 10 metres from the edge of the field. They should also be placed in areas known to be infested in previous years. Traps should be set up in the last week of June in southern New Brunswick and in the first week of July in the northern part. They should be inspected three times a week.

The first spray should be applied within 5 to 7 days after the first adult capture where a zero tolerance for maggots is desired, or if the field has had a prior history of maggot infestations. Otherwise, the traps should continue to be inspected. A spray should then be applied when the number of fly captures reaches an average of one per trap per day. The traps should continue to be inspected to determine whether or not a second spray is required. Flies should be removed from traps when inspected to make it easier to determine fly captures. A second spray should be applied within 7 to 10 days after the first spray if there is an average of one fly caught per trap per day. Data should be recorded for future reference. Traps should be replaced every 2 to 3 weeks since they will deteriorate in wet weather and get covered with other types of insects. Therefore, two or three traps should be expected to be used per trap location per season.

Monitoring provides information on the relative abundance of flies and their emergence dates. This information allows the grower to use insecticides at the appropriate time and avoid their unnecessary use.

A previous method of determining when to spray was based on fruit development. A spray was applied within one week after the first blueberries started to turn red. A second spray was applied in heavily infested fields within 7 to 10 days after the first spray. The present trap method provides more accurate information.

Monitoring Sprout Fields. Recent studies have investigated the possibility of controlling blueberry maggot adults in sprout fields. The idea is based upon spraying for adults before they fly to crop fields. Both sprout and crop fields are monitored. The sprout field is monitored, as previously described for crop field monitoring, and sprayed within 5 to 7 days after the first adult capture. The crop field is monitored and sprayed only when the number of fly captures reaches one per trap per day. Greatest control problems occur in the first year of this modified program. Consequently, it is often necessary to spray both sprout and crop field sections of divided fields during the first year. This method has been successful in the elimination of a spray to nearby crop fields with resulting maggot infestations from zero to a few maggots per litre of berries. This program is useful where markets allow for low levels of maggot infestations. When successful, the modified program eliminates the need to spray a crop field and avoids the risk of insecticidal residues on fruit. Greatest success is likely to occur in isolated fields where monitored fields cannot be contaminated by high populations of flies from blueberry fields which are not under the grower's control.

Evaluation. Blueberry maggot monitoring and the spray program should be evaluated by determining infestation levels of maggots in blueberries. At least two one-litre samples of wild blueberries per hectare should be taken and analyzed prior to harvest. The method is described in the fact sheet: Detecting Maggots in Wild Blueberry Fruits (C2.4.0). This will aid in locating problem field areas in succeeding crop cycles.

Control. Proper pest management results in the combined use of all the management practices previously described: pruning every second year, complete removal of berries at harvesting, weed control, monitoring, identification of adults, spraying, evaluating. Weedy field border and abandoned field areas may also be sprayed for maggots. Fields that are not divided into sprout and crop sections will allow for more effective control of the blueberry maggot, since most flies emerge from sprout field sections.

Insecticide recommendations and rates are listed in the Lowbush Blueberry Protection Guide (Fact sheet C1.6.1 in this series). Further information can be obtained from the agricultural representatives listed in the guide.

¹ The use of trade names in this publication is solely for identification purposes and does not imply endorsement of the products named or criticism of similar products not mentioned.

Fig. 1 Larval stage of the blueberry maggot	Fig. 2 Adult blueberry maggot
Fig. 3 Wing pattern of the blueberry maggot (above) & black cherry fruit fly (below)	Fig. 4 Blueberry maggot trap

References: USDA, Tech. Bul. No. 275, 1932; Maine Agr. Exp. Sta. Bul. 500, 1952; Canadian Agricultural Insect Pest Review, Vol. 64, 1986; Atlantic Agriculture, fact sheet ACC.-1018, 1986; Univ. of Maine, fact sheet No. 201, 1987; Agr. Can. Pub. 1477/E, 1989; Agriculture & Agri-Food Canada, Summary of Plant Pest and Disease Situations in Canada, 1994; NS Dept. Agr. & Marketing, Blueberry Fruit Fly Fact sheet, 1995; PMAO, The Management of Blueberry Insect Pest Workshop Report, 1995.

Prepared by: Christopher Maund, P.Ag., Provincial Entomologist, N.B. Department of Agriculture & Rural Development; Evans Estabrooks, P. Ag., Research Horticulturist, Agr. & Agri-Food Canada Research Centre Fredericton; Gaétan Chiasson, P. Ag., Horticultural Specialist, N.B. Department of Agriculture & Rural Development.

Winter 1996