Syrphidae of Mid-Atlantic Apple Orchards
Syrphid flies, or hover/flower flies, are very common and
conspicuously colored flies. Many
adults appear as bee mimics and contribute to pollination in various cropping
systems. Adults feed on pollen, nectar,
and sugars such as honeydew of aphids.
Syrphidae can usually be identified by the spurious vein (“false vein”)
that runs between the radial and medial veins and typically crosses the r-m
cross vein (except some exotic species where the spurious vein is very faint).
Larvae of Syrphidae can be phytophagous, saprophagous, or
entomophagous. The aphidophagous
(“aphid-eating”) adults deposit their eggs directly next to, or in aphid
colonies to limit searching by the blind larvae. The larvae search for prey by
a method known as “casting”, where the front of the body is swung side-to-side
until contacting prey. Oral hooks are
then inserted into the body of an aphid and it is sucked dry. In the mid-Atlantic region many species of
syrphid flies can be encountered, but this page will focus mainly on
aphidophagous syrphid fly larvae.
Heringia calcarata (Loew)
is the most abundant aphidophagous syrphid fly found in mid-Atlantic apple
orchards. Unlike many syrphid flies, H. calcarata is black. Adults (Figs. 1 and 2) are about 9 mm in
length and complete development in approximately 25 days. The eyes (holoptic, tend to be more reddish)
of males touch at some point on the head, whereas those of the female
(dichoptic, tend to be burgundy) do not.
The egg (Fig. 3) is approximately 0.64 mm long x 0.24 mm wide and has
unbroken longitudinal ridges running along its surface. This species is a specialist of the woolly
apple aphid (WAA) (Eriosoma lanigerum
(Hausmann)). Females lay eggs directly
into WAA colonies where the larvae feed for approximately 9 days before
pupariating in the soil or on limbs. H. calcarata is a member of the Pipizine
tribe of syrphid flies, which are known to prey on colonies of aphids producing
waxy, flocculent material and/or galls such as WAA. Edaphic (root) colonies of WAA will continue to be an increasing
problem in orchards with the prevalent use of dwarfing rootstocks, not bred for
resistance to the WAA. Thus, H. calcarata may become a valuable asset
in control of root aphid colonies. H. calcarata is most likely bivoltine
and numbers tend to peak right before population increases of the WAA, in early
June and early July. In conjunction
with Aphelinus mali, H. calcarata can effectively control
arboreal WAA populations.
Fig. 1 Adult Male - H. calcarata
2 Adult Female - H. calcarata
Egg – H. calcarata
Fig. 4 Larva – H.
5 Puparia – H. calcarata
Eupeodes americanus (Wiedemann)
is a generalist aphidophagous syrphid.
The “American Hover Fly” feeds on WAA, rosy apple aphid (RAA), and
spirea aphid (SA) in orchards. It is
the most abundant generalist found in the mid-Atlantic orchards, but far less
than the specialist H. calcarata. This species is found early in the season in
WAA colonies, but then switches to RAA and SA later in the season (mid-June),
returning to WAA around the mid to last part of September when WAA populations
resurge. It can be grossly differentiated
from Syrphus rectus (seen below) by a
dark stripe down the front of the face of the adult (Fig. 6a). The egg (Fig. 7) is approximately 0.96 mm
long x 0.26 mm wide and has broken longitudinal ridges running along its
surface. The larva (Fig. 8) is blackish
with orange markings on the body, tends to look somewhat spiky, and is narrower
than that of S. rectus. The puparia is grayish-orange and appears
mottled, much like the larva (Fig. 8a).
First instars are difficult to separate if they were not seen emerging
from an egg.
Fig. 6 Adult dorsal – E. americanus
6a Adult ventral – E. americanus
Fig. 7 Egg – E. americanus
Larva – E. americanus
8a Puparia- E. americanus
Syrphus rectus (Osten
is also a generalist aphidophagous syrphid fly that can be found feeding on
WAA, RAA, and SA colonies in apple orchards.
This species is only prevalent in WAA colonies for 2 weeks in May and
then switches to RAA colonies. During
those 2 weeks, the population numbers are sparse and are a minor component of
the predator complex. However, this
species is quite common in RAA and SA colonies. The adult (Fig. 9a) can be grossly differentiated from E. americanus by lacking a dark stripe
down the front of the face (Fig. 9b).
The egg (Fig. 10) is approximately 1.19 mm long x 0.44 mm wide and has
“T-shaped” projections covering its surface.
The larvae (Fig. 11) are wider (later instar) than E. americanus and tend to be yellow-pale yellow in color.
9a Adult dorsal – S. rectus
9b Ventral - S. rectus
10 Egg – S. rectus
11 Larva – S. rectus
Allograpta obliqua (Say)
A. obliqua is
a very sporadic aphid predator. They
are not found as often in mid-Atlantic orchards as other generalist predators
and even then are primarily found in RAA colonies. The larvae and puparia are quite distinct, in that they are
totally green. The adult (Fig. 12) has
a fairly narrow abdomen and a characteristic pattern on the fourth abdominal
12 Adult – A. obliqua
Some other common
syrphid fly species, though probably not aphidophagous in apple, found in
mid-Atlantic apple orchards are Toxomerus
marginatus, Toxomerus geminatus, Platycheirus obscurus, and Sphaerophoria spp.