Syrphid Flies

Syrphid flies, also known as hover flies for their ability to hover in flight, are common predators of aphids and other soft bodied insects. Adults are usually bee mimics (picture at top ). Three of the more common species are Syrphus rectus Osten Sacken (see egg and larva below), Allograpta obliqua (Say) and Eupeodes (formerly Metasyrphus) americanus (Weidemann). A. obliqua may complete development from egg to adult in less than 21 days. Various stages overwinter, depending on species, giving rise to adults in spring. Adults feed on pollen, nectar and aphid honeydew. Females must feed on pollen for proper egg maturation. Females oviposit in the midst of aphid colonies, using honeydew as an ovipositional stimulant, and laying hundreds of eggs each. Eggs are often the first sign of aphid predators seen in the spring (left picture below). Eggs are white, elliptical, and about 4/100 inch (1 mm) in length. There are three larval instars. Larvae are elongate, tapering gradually toward the head end (right picture below). Larvae search for prey by casting the forward end from side to side; prey must be contacted directly to be detected. Larvae pierce aphids with their mouth hooks, sucking fluids from the bodies before moving to other prey. Each larva may consume hundreds of aphids during its development. Larval feeding success influences future fecundity. Third instar larvae have the greatest impact on aphid numbers. Larvae of some species are relatively plump. There may be 5-7 generations per year. Multivoltine species overwinter as adults, univoltine species as third instar larvae. These are among the most voracious of aphid predators.

Additional information was developed by Brent Short and Chris Bergh on syrphids in apple orchards in northern Virginia, as a part of "Arthropod Management in Fruit Crops", ENT


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