Aphidoletes aphidimyza

Target Pest: Aphids

Description: Aphidoletes larvae are voracious native predators of over 60 species of aphids. The larvae are legless maggots about 3 mm long, and orange in color which make them easy to spot in foliage. Adults are small midges resembling mosquitos that are nomadic (they will seek out heavy aphid populations to lay eggs near) and can be hard to find. They are most easily spotted in the evening, and may be found hanging (unstuck) from spider webs were mating often takes place.

Use in Biological Control: Aphidoletes are used to control aphids indoors in commercial greenhouses and interior plantscapes. They may also be used outdoors in zoos, orchards, shade trees, roses, home gardens, and botanical gardens.

Optimum conditions for Aphidoletes are 70-77° F (21-25° C) and relatively high humidity (70%). This is especially important 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 overwintering predator populations that will be active early the following spring. 

Life Cycle: The complete life cycle takes 24 days at 70°F (21°C), but can vary depending on temperature and availability of prey. Sex rations may vary, but there are usually more (60%) females. Females lay eggs on leaves beside aphids (150-200 in a lifetime), which are shiny orange ovals, less than 0.3 mm long.

At optimal temperatures, the eggs will hatch in 2-3 days and the tiny, legless larvae crawl along the leaf in search of aphids. They 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 up to 50 aphids per day.

Where aphid populations are high, they will kill many more aphids than they can consume. To pupate, larvae drop to the ground and burrow into the top ½ inch of planting medium to spin a cocoon. Adults will emerge in 2-3 weeks. Because of the “drop”, planting medium needs to viable for them to burrow. Hydroponic and other similar systems should be verified for effectiveness before beginning program with Aphidoletes.

When used outside, the last generation of Aphidoletes in the fall will over-winter in cocoons in the soil. They are very hardy and will re-emerge in the spring as adults to find new aphid populations. Because of this, the same population is viable for more than one season. 

For Best Results: Using preventatively will reduce aphid hot-spots from developing into problem areas. When aphids are found, continue to make these releases away from aphid infestations. This will allow Aphidoletes to search out any new infested areas.

During fall and winter, the 2^nd generation of Aphidoletes will diapause in short day conditions, unless 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 meter diameter, as long as the night temperatures are above 60°F (15°C).

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 organic materials are added. Adding a thin layer (1/8 in.) of sand, sawdust, or other organic material under the leaf zones of plants will improve the cycling of Aphidoletes.

For control of cotton/melon aphid (which reproduce very quickly), Aphidoletes should be used along with Aphidius parasitic wasps and ladybeetles. It may be necessary to control ants in conservatories and around outdoor trees because they can protect aphid colonies by removing predator larvae. 

Introcuction Rates: Generally, Aphidoletes should be released in the spring before the first sign of aphid infestations. Once aphids are detected, additional releases should be made (2-3 times at 7-10 day intervals) in the aphid areas to establish the predator. Further, recent research has indicated that in greenhouses, low level (0.25-0.5 Aphidoletes/sq. meter), weekly preventative releases will prevent the build-up of most species of aphids.

Greenhouse Vegetables: In crops where aphids have been a problem in the past, weekly preventative releases (listed above) will help maintain control. For preventative releases, use two release points per hectare, and release in areas where aphids have not been established. Do not release directly under circulation fans. Once aphids are detected, use the following rates in the infested areas: Tomato: 100 Aphidoletes/ infested plant, weekly for 3 weeks

Pepper: 100 Aphidoletes/infested plant, weekly or until established Cucumber: 10 Aphidoletes/plant, weekly in infested areas only until established

Flower & Ornamentals: Use preventively at low rates weekly or bi-weekly before aphids appear. Once aphids are detected, continue preventative releases and add additional releases of 100-1,000 in hot spot areas.

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 per plant, weekly for 3 weeks For large areas (such as apple orchards), use 5,000- 10,000 Aphidoletes per hectare (1,000-4,000/ acre), repeated 1-3 times, 1-2 weeks apart, or until established. For outdoor use, keep the Aphidoletes in a warm spot (72-77°F/ 22-25°C) until they have all emerged. Next, 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.