 
Left: Aphidoletes egg laid near aphid. A.T. Eaton
Right: Aphidoletes larva. J.Ogrodnick
Aphidoletes aphidimyza
(Diptera: Cecidomyiidae)
The aphid midge, Aphidoletes aphidimyza, is a cecidomyiid fly
whose larvae are effective predators of aphids. Initially a new species
was described for every different prey attacked, and at least 24 previously
described species have been determined to be A. aphidimyza. This
midge is an important component of biological control programs for greenhouse
crops and is widely sold in the U.S.
Appearance
Adult aphid midges are small (2-3 mm), delicate, mosquito-like flies
with long, dangling legs and long antennae. Eggs are oval, minute (about
0.1 mm by 0.3 mm), and orange. The larvae, which look like orange maggots,
are tiny, growing through three instars from minute to 2-3 mm. Depending
on their food source, they are bright orange to red, and their bodies narrow
toward the head. The larvae have strong "jaws" with which they
grasp their prey.
Habitat (Crops)
Cole crops, potatoes, greenhouses, backyard gardens, ornamentals, orchards,
berries. In the greenhouse A. aphidimyza has become very important
for aphid control on long term vegetable crops. Although very few field
introductions have been reported, studies indicate there is the potential
for aphid control in many outdoor crops. A. aphidimyza has been
found on cabbage, apples, blueberries, and ornamental bushes, and is recognized
as being an important naturally occurring control agent of aphids on Russian
and Egyptian cotton.
Pests Attacked
Life Cycle
Each female may live for one to two weeks and deposit, singly or in
clusters, about 70 upright, orange eggs on leaves among aphids. The eggs
hatch in two to four days. The midge larva paralyses each aphid by attacking
its leg joints and then sucks it dry, leaving a blackened, collapsed aphid
attached to the leaf.
In greenhousese the larvae drop to the soil less than a week after hatching
and burrow to pupate; adults emerge about one to two weeks later. In the
field, larvae develop in one to two weeks, and pupation may take up to
three weeks. The life cycle in the field may range from three to six weeks,
and there may be three to six generations per year, depending heavily on
daylength.
Adult midges fly at night and are rarely seen; they feed on honeydew.
Aphid midges overwinter as larvae in cocoons in the soil, pupating in spring.
Adults emerge in late spring, mate the night of emergence, and the mated
females begin the search for aphids. Most eggs are laid during the first
few days after emergence.
Relative Effectiveness
Adult midges are very efficient at locating aphid colonies. In one study,
A. aphidimyza located the one infested plant out of 75. One larva needs
a minimum of 7 aphids in order to complete the life cycle, but it may eat
as many as 80. In addition, larvae kill more aphids than they consume.
Greenhouse vegetable integrated pest management programs in Canada recommend
the use of these midges, often in conjunction with releases of the parasitoid
wasp, Aphidius matricariae, for aphid control. The larvae are most
common from mid- to late summer in the field. Mass released aphid midges
have adequately controlled aphids in small backyard garden trials.
The onset of shorter daylength toward the end of summer can induce diapause.
This can be averted in the greenhouse by nocturnal use of 100 W incandescent
light bulbs spaced 22 m apart when the canopy is open, with closer spacing
when the canopy is dense.
Pesticide Susceptibility
Conservation
Aphid midges are native to much of North America and will overwinter,
although winter mortality may be high. High humidity and shelter from high
temperatures and strong winds will encourage midge activity. In greenhouse
environments, adult midges are most effective at 20-26 degrees C with high
humidity. Adults also need a source of honeydew for feeding and to improve
egg laying. Larvae need slightly moist soil for successful pupation.
For general information about conservation of natural enemies, see Conservation in the Tutorial section on this site, or the Volume II, No. 1 Feature Article on conservation in the Midwest Biological Control News Online.
Commercial Availability
Aphidoletes aphidimyza is commercially available (see the off-site
publication, Suppliers
of Beneficial Organisms in North America). The midges are shipped
as pupae in a moist carrier material, such as vermiculite. Sand or vermiculite
may adhere to the pupal cases.
Acknowledgments
Thanks for reviewing this section to Richard Meadow, Department of Entomology
and Nematology, Norwegian Crop Research Institute, Fellesbugget, Norway,
and John Sanderson, Department of Entomology, Cornell University.
Adapted from:
Additional References
Gilkeson, L.A. and Hill, S.B. (1986) Diapause prevention in Aphidoletes
aphidimyza (Diptera: Cecidomyiidae) by low-intensity light. Environ
Entomol. 15: 1067-1069.
Meadow, R.H. (1984) The effect of the aphid midge Aphidoletes aphidimyza
(Rond.) on populations of green peach aphid (Myzus persicae) (Sulz.)
on tomatoes and bell peppers. Masters thesis, Cornell University, Ithaca,
NY.
Metcalf, R.L and Metcalf, R.A. (1993) Destructive and Useful Insects:
Their Habits and Control. McGraw Hill, Inc., New York, NY. 1073 pp.
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