 |
||||
 |
Back to Predators Table of Contents
Aphidoletes aphidimyza 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 A. aphidimyza attacks over 60 species of aphids.
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 Most sprays are toxic to midges. Adults may be more susceptible than larvae.
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, Feature Article on conservation in Volume II, No. 1 of Midwest Biological Control News.
Commercial Availability Aphidoletes aphidimyza is commercially available (see the off-site publication, Suppliers of Beneficial Organisms in North America, page of the California Department of Pesticide Regulation website). 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.
Taken from: Hoffmann, M.P. and Frodsham, A.C. (1993) Natural Enemies of Vegetable Insect Pests. Cooperative Extension, Cornell University, Ithaca, NY. 63 pp.
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.
Back to Predators Table of Contents
|
|
||
 |
||||
