The blueberry maggot (Rhagoletis mendax Curran) is a common pest of blueberries in Canada and the northern United States. Although its range seems to be expanding southward, infestations tend to be localized and sporadic in the South. The adult is a small, black fly, about 4 mm (3/16 in.) long. It can be recognized by a distinctive pattern of black bands running diagonally across each wing, by white bars on each side of the thorax, a white spot at the posterior tip of the thorax, and white lines along the back edge of each abdominal segment. Larvae develop entirely within the blueberry fruit and grow to about 1 cm (1/2 in.) in length. They have tapered, wormlike bodies with no legs, eyes, or antennae.
- Adult stage of the blueberry maggot.
- Larval stage of the blueberry maggot.
- Wing patterns of flies commonly found on sticky traps.
Life Cycle and Seasonal Distribution
Blueberry maggots overwinter as pupae buried 2.5 to 15 cm deep (1 to 6 in.) in the soil (Lathrop and Nickels 1932). Warm temperatures in the spring trigger pupal development (Tomlinson 1951), and the adult flies usually begin emerging shortly after highbush berries start to ripen. After a 7-10 day pre-oviposition period, female flies begin to lay eggs on large, ripening berries. Larvae hatch in about 5 days, burrow into the berry, and feed on the pulp for about two weeks. Mature larvae drop out of the berry and burrow into the soil to pupate. There is only one generation per year, but a few pupae may remain in the soil for 2 or 3 years (Lathrop and Nickels 1932).
Symptoms and Damage
During the early stages of the maggot's development it is nearly impossible to separate infested from non-infested fruit. If wormy berries are havested and packaged with sound berries, the larvae will continue to mature within the fruit and may emerge for pupation at the point of sale. Eventually, the pulp of an infested berry becomes extremely soft and watery, but growers are not likely to notice this symptom before harvest.
Biological control agents for the blueberry maggot include ants, spiders, and a small parasitic wasp, Opius melleus (Lathrop and Nickels 1932). The ants and spiders may prey on either adult flies or on mature larvae that drop to the ground. Parasitic wasps attack younger larvae in the fruit. The female wasp pierces a berry with her long ovipositor and lays an egg directly on the maggot's body. In general, rates of predation and parasitism are too low for effective suppression of maggot populations (Boller and Prokopy 1976).
Scouting, Management, and Control
Infestations of blueberry maggot can be detected before they reach damaging levels by trapping the adult flies on yellow sticky boards (2-4 traps per acre) baited with ammonium acetate or protein hydrolysates (Howitt and Conner 1965, Neilson 1984). A treatment threshold of three adults per trap per week (or five adults per field per week) gives adequate lead time for chemical control if the traps are in place before the first flies emerge.
Some blueberry fields are more likely to develop a maggot infestation than others. In general, sites where large bushes shade the ground through most of the day seem to provide optimal habitat for maggot survival. A statistical model can be used to estimate infestation probabilities for different sites based on bush height and row spacing. The model has proven to be quite reliable for non-irrigated fields in southeastern North Carolina. Further information about predicting blueberry maggot infestations can be found in the Department of Entomology's Fruit Insect Note #B-2.
When control is necessary, a short-residual pesticide should be used as a foliar spray to protect the fruit. Apply this spray from the ground whenever possible to get maximum coverage on the lower half of the bushes. Use a ULV spray by air only when weather, labor, or harvest conditions make ground sprays impractical. Tank mixing an insecticide with a bait formulation containing protein hydrolysates can improve efficacy by making the spray residue more attractive to newly emerged adults. Spot infestations can be eradicated if they are sprayed every 7 to 10 days until no fruit at all remains on the bushes.
- Boller, E. F., and R. J. Prokopy. 1976. Bionomics and management of Rhagoletis. Ann. Rev. Entomol. 21: 223-246.
- Howitt, A. J., and L. J. Conner. 1964. The response of Rhagoletis pomonella (Walsh) adults and other insects to trap boards baited with protein hydrolysate baits. Proc. Entom. Soc. Ont. 95: 134-136.
- Lathrop, F. H., and C. B. Nickels. 1932. The biology and control of the blueberry maggot in Washington County, ME. USDA Tech. Bull. 275. 77 pp.
- Nielson, W. T. A. 1984. Capture of blueberry maggot (Rhagoletis mendax) adults on Pherocon AM traps and on tartar red sticky spheres in low bush blueberry fields. Can. Entomol. 116: 113-118.
- Tomlinson, W. E. 1951. Influence of temperature on emergence of the blueberry maggot. J. Econ. Entomol. 44: 266-267.
Last updated: 2 June 1997
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