Tip Top Bio-Control Technical Bulletin
Aphidoletes (Aphidoletes aphidimyza)
Aphid Predatory Midge
Many species of aphids.
Aphidoletes larvae are voracious native predators of over 60 species of aphids. Larvae are orange, legless maggots, up to 3 mm (1/16 inch) long.
Adults are small, delicate midges (flies) 2-3 mm (1/16 inch) long, with long legs. The males have long antennae, which are covered with hairs. The females have shorter and thicker antennas. The eggs are very small and orange colored. Adults are rarely seen, as they are mostly active in the evening.
Use in Biological Control:
Aphidoletes are used to control aphids indoors in commercial greenhouses and interior plantscapes as well as outdoors in orchards, shade trees, roses and home gardens. Optimum conditions are 21°-25°C (70°-77°F) and high relative humidity (over 70%), particularly for the pupal stage, which must not dry out.
If aphids are present in outdoor plants in late summer, a release of Aphidoletes at this time helps reduce the overwintering aphid population, while establishing an overwintering predator population that will be active early the following spring.
Using 10 -15 X hand lens, full-grown larvae are relatively easy to see among the aphids because of their characteristic orange color.
Younger larvae are much smaller and pale in color, making them very difficult to see.
A complete life cycle takes 21 days at 21°C (70 °F). Development rate depends on temperature and availability of prey.
Sex ratio in populations vary, but there are usually somewhat more females (60% females).
Female midges lay their eggs on leaves beside aphids. Each female lays 150-200 eggs during her lifespan of 1-2 weeks. The eggs are shiny orange ovals, less than 0.3 mm (1/50 inch) long.
At 21°C, eggs hatch in 2-3 days and the tiny, legless larvae crawl along the leaf in search of aphids.
Larvae feed by biting aphids and paralyzing them with a toxin before sucking out the aphid body fluids. They feed for 7-10 days and can kill 3-50 aphids per day. Where aphid populations are high, larvae kill many more aphids than they can consume.
To pupate, larvae drop to the ground and burrow into the top 1-2 cm (1/2 inch) of soil or organic material to spin a cocoon. Adults emerge in 2-3 weeks.
Outdoors, the last generation of Aphidoletes in the fall overwinters in the cocoons in the soil. They are very hardy and survive outside throughout the cold/warm growing regions.
Aphidoletes respond to cool temperatures and shortening day lengths (less than 16 hrs) by entering diapause (like a hibernation state), therefore in most greenhouse they are only active from mid-March to September unless supplemental lighting is used.
Aphidoletes are sent as pupae (cocoons) in moist vermiculite or sand. The predators may be released in either of two ways:
Hold containers at 22°C (70°F) temperature until a few adults are seen flying in the container, then place the opened container in the shade in the greenhouse or garden.
Immediately upon receipt, gently sprinkle the vermiculite carrying the cocoons onto the surface of the soil or growth media, in the shade; keep the vermiculite moist (not wet) until adults have emerged.
Adults should begin to emerge within 1 week and all should emerge within 14 days of receipt.
Generally, Aphidoletes should be released in the spring, 2 or 3 times at 7-10 day intervals to establish the predator.
Tomato – 1 Aphidoletes/6 plants, weekly for 2 weeks
Pepper – 1 Aphidoletes/plant, weekly or until established
Cucumber – 10 Aphidoletes/plant, weekly in infested areas only until established.
Gardens – 250 Aphidoletes/aphid hot spot, weekly for 2 weeks
Orchards – 5-10 Aphidoletes/tree, weekly for 3 weeks
Shade trees/5-10 Aphidoletes/tree, weekly for 3 weeks
Roses – 3-5 Aphidoletes/plant, weekly for 3 weeks
For large areas, such as apple orchards, use 1,000-4,000 Aphidoletes/acre, repeated 1-3 times, 1-2 weeks apart or until established.
For outdoor use, release during the evening on the upwind side of the planting so that the prevailing winds will help to disperse the midges throughout the plot.
For Best Results:
Because they diapause in short-day conditions, Aphidoletes should only be introduced in greenhouses during fall and winter if there is supplemental lighting. It has been found that leaving on one 60-watt light bulb all night will prevent diapause in more than half of the larvae within a 20 m (20 yd) diameter circle as long as night temperatures are above 15°C (60°F).
The larvae need to burrow into damp soil, peat moss, sawdust or other growth media to pupate. In greenhouses with bare plastic or concrete floors, survival will be low unless such organic materials are provided. Adding sand, sawdust or other organic materials under the leaf zones of plants will improve reproduction of Aphidoletes.
For control of cotton/melon aphid, which reproduces very quickly, Aphidoletes should be used along with Aphidius parasitic wasps.
It may be necessary to control ants in conservatories and around outdoor trees because they can protect aphid colonies by removing predators.
For additional control of aphids, pirimicarb (i.e., Pirliss) may be used. It is slightly toxic to Aphidoletes, but the repellent effect of the pesticide disperses the aphids and has been found to repel Aphidoletes females from laying eggs on leaves with pirimicarb residues therefore avoid frequent use.
Insecticidal soaps are harmful to all stages of Aphidoletes, but have no residual effect.