The blueberry maggot, Rhagoletis mendax (Curran), is the major pest of blueberries in many parts of the Northeast; however, blueberry plantings in Pennsylvania have not been heavily attacked to date. The presence of infested fruit at harvest can result in the condemnation of whole fields of harvested fruit. Moreover, the control of the insect is complicated by its long emergence period, its migration tendencies, and the fact that it usually does not attack fruit until after harvest has begun.
The female fly is about 3/16 inch long. The abdomen is pointed and black with white cross bands. The wings are clear and marked with heavy black bands in the shape of an upside-down "W." Several other species of fruit flies can be confused with blueberry maggot if they are not inspected carefully.
Overwintering as pupae buried anywhere from just beneath the leaf litter to 6 inches deep in the soil, the blueberry maggots emerge from the soil as flies in June or July. After emerging, the flies, which live for about 30 days, spend the first 2 weeks resting and feeding on nectar, dew, and honeydew. Mating takes place near the end of this resting period, and females seek large, ripened berries in which to lay eggs. The female pierces the skin of the fruit with her egg-laying apparatus and deposits a single egg in each berry. Each fly may lay up to 100 eggs in a 2- to 3-week period. Upon leaving the berry, the female deposits a chemical that deters other flies from laying eggs in that berry. The egg hatches in about 5 days, and the larva burrows into the berry and feeds on the pulp for about 2 weeks. The mature larva leaves the berry and drops to the soil to pupate and remain until the next summer. Only one generation hatches each year, but a few pupae may remain in the soil for 2 to 3 years.
The potential for infestations of blueberry maggots can be assessed by trapping adults before their numbers reach damaging levels. The traps are yellow sticky boards placed near the planting at least a week before the first flies are expected to emerge (early June). These boards are baited with a feeding attractant--either ammonium acetate or protein hydrolysates. Baited traps can be purchased or made. Trapping should continue through harvest, and the traps should be replaced every 3 weeks or when they become clogged with insects. The flies on each trap should be counted and removed each week. Insecticides should be applied when three adults per trap per week or five adults per field per week are found. Note: Several other fly species will be trapped on the boards (along with other insects). Make sure that only blueberry maggot flies are counted. If species identification is a problem, consult your county extension agent.
If control is necessary, a relatively nontoxic, short residual insecticide should be used so that it does not interfere with harvest. If ripe berries are present, they should be harvested before the spray is applied. Tank-mixing the insecticide with protein hydrolysate will increase the treatment efficacy. Once spraying has begun, it should be continued with an application every 7 to 10 days until all unharvested fruit has dropped.