Aphid midge, Aphidoletes aphidimyza (Rondani)

The aphid midge is a cecidomyiid fly. Although most species in this family form plant galls, this species is free-living and feeds on aphids, often providing important biological control. Massachusetts research has shown that predator-prey ratios of at least 1 larva to 15 aphids are suitable for control. Pupae overwinter in the orchard. Adults somewhat resemble mosquitoes and are seldom noticed. They are nocturnal. Larvae are slender orange maggots, about 1/10 inch long (2 mm), found in aphid colonies (Plate 151). They may be very common, especially in low-spray, IPM blocks. Mean fecundity exceeds 200 eggs per female. Eggs are reddish-orange and may be laid singly or in groups, in numbers proportional to aphid density. Larvae may detect prey within only a very limited area. After a larva grasps an aphid, a toxin is injected which immobilizes the prey. The larva may feed on a single aphid for several hours to a day. The rate of kill depends on the size of prey. One study reported larvae killing 5.2 large or 14.7 small green peach aphids per larva. Killing rates of 40-80 aphids per larva have been reported. Some disagreement may arise from the fact that at high prey densities, aphid midge larvae will kill more than they consume, partially consuming or leaving uneaten some prey. Nevertheless, this level of individual voracity is low relative to some other groups of aphid predators. However, larvae are able to complete development at fairly low prey densities, a desirable trait for biological control. The larval developmental period is 12-17 days; 15-32 days are spent as pupae.

One Canadian study reported that complete aphid control was achieved in a few days at ratios of 5 apple aphids per midge egg. Partial control was provided at 8-12 aphids per egg, and no control was provided by 12-14 aphids per egg. Massachusetts research has shown that predator-prey ratios of at least 1 midge larva to 15 aphids are suitable for control.

This species appears well suited to our orchards with normally high humidity. This species overwinters in the orchard but may not become active early enough (mid-June in Massachusetts) to provide early-season control. Late instar larvae are stimulated to enter diapause by decreasing light levels in the fall. In the fall, mature larvae descend to the soil where a cocoon is formed. Pupation occurs in the spring.

See image in Alaska site.

from a chapter in the Mid-Atlantic Orchard Monitoring Guide, entitled Aphid Predators,
by D. G. Pfeiffer and H. W. Hogmire
E-mail to: Douglas G. Pfeiffer