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