Aphid control

Aphido-line a

Aphidoletes aphidimyza

How does it work.

Adults of Aphidoletes aphidimyza are delicate flies thatwhich belong to the same group as the fungus gnats or gall midges. The nocturnal adults themselves are not predatory, but they lay eggs amongst colonies of aphids, , and the larvae,, which hatch from these eggs, attack and feed on members of the colony. . They are reported to feed on more than 60 different species of aphid, including all the most important species encountered in protected crops.

Adults are attracted by, and feed on, aphid honeydew, and this feeding extends adult life and increases the number of eggs the females are able to lay. The species of host aphid also has a marked affect on the production of eggs, as does the density of the aphid colonies.

Between 40 and 250 eggs are reported to be laid, and more eggs are laid in denser colonies. The eggs hatch after 2 days at 23°C, and the resulting larvae are fully grown within 6 days. At higher temperatures, larval temperatures, larval development is shorter, taking only 3 days at 27°C. This development extends to 9 days at 15°C. Fully fed larvae then dropdrops to the ground and pupatepupates within a silken cocoon in the upper layers of the soil. When fully developed, approximately 14 days later, fresh adults emerge from the cocoons. They must reach the soil surface in order to expand their wings, and can then mate and begin to lay eggs. Most emergenceemergenceemergences occursoccur during the late evening,, and mating occurs shortly afterwards. Unmated females cannot produce viable eggs.

Larvae attack aphids by biting the joints of the legs, and injecting a toxin, which paralyses the aphid. The aphid may leave the site of the attack, but will be followed by the predator until it ceases to move. The body contents of the aphid are then drained. It is known that a single larva of Aphidoletes aphidimyza can reach maturity on as few as five individuals of the aphid Myzus persicae.

The size of the aphids available will, of course influences the number attacked and eaten, but it is known that, in dense aphid colonies, Aphidoletes larvae will kill far more aphids than they eat. A single larva may kill more than 35 aphids during its life. This is extremely important for control, becauseas it improves the efficiency of the predator at high prey densities, while allowing it to persist at lower prey densities.

As day lengths decrease in autumn, the pupae of Aphidoletes aphidimyza enter diapause. This diapause restricts the use of the predator in crops where there is no supplementary lighting, but even low light intensities may be sufficient to prevent diapause induction.

When and where should you use it?

Aphidoletes aphidimyza can be used in any situation where aphids present a problem, and in which there is some tolerance of aphid infestation. It is ideally suited for use where aphid populations are high, and is suitable as a corrective treatment where aphid parasitoids have not given sufficient control. It should be released between March and September only, unless supplementary lighting is available

How should you use it?

Humidity is important for the successful emergence of Aphidoletes adults from the cocoon. Tip small quantities of vermiculite and Aphidoletes cocoons into Universal Release Boxes adjacent to aphid colonies, or place the mixture onto moist peat, potting compost or directly onto the growing medium in the shade. The majority of the adults will emerge during a short period after release. Best emergence is achieved with wet vermiculite. Desiccation of the vermiculite will reduce the percentage emergence of the pupae. Depths of vermiculite greater than 3 cm will reduce the number of adults successfully escaping from the carrier material. Conversely, very shallow layers will dry out quickly, and also reduce emergence.

Because Aphidoletes larvae are present as active predators on the plant for only a few days, and remain as pupae in the soil for a large part of their life, it is essential to make more than one release to ensure continuous control of the pest. A single release may result in a decrease in the aphid population, followed by a resurgenceresurgence as the majority of larvae leave the plants to pupate.

The rate of application should be at least 10/m² in and around aphid colonies. Lower rates of 5/m² may be used more widely in the crop. Higher release rates will result in more rapid control of the aphid problem, while low rates may fail to control rapidly growing aphid populations.

The use of plastic mulches on the soil will interfere with pupation in the soil, and so may reduce or prevent the establishment of Aphidoletes.

When should you not use it, and what are the control options

Do not release Aphidoletes aphidimyza before aphids are seen in the crop nor on crops where there is no tolerance of aphids, as is the case on many ornamental plants.

Preventive control of aphids should be achieved with low rate releases of the parasitoids, Aphidius colemani, A. ervi and Aphelinus abdominalis, depending on the species of aphid concerned. Corrective treatments may also be made with larvae of the lacewing Chrysoperla carnea, with the ladybird beetle Adalia bipunctata, or with specific insecticides such as pymetrozine.

The occurrence of diapause in autumn and winter prevents the use of Aphidoletes during the winter, except where there is supplementary lighting.

What will it do?

When used as recommended, Aphidoletes aphidimyza will reduce established colonies of aphids , and may limit or prevent the appearance of further colonies elsewhere in the crop.

What will it not do?

Aphidoletes aphidimyza will not establish in low aphid populations, and is not recommended for preventive use. It cannot immediately prevent continuing aphid damage on crops where it is released, and should not be used where there is very low tolerance of aphids. The establishment of Aphidoletes will be reduced by the use of plastic mulches, which will interfere with pupation in the soil.

Chemical compatibility.

Aphidoletes aphidimyza is sensitive to many commonly used insecticides. There are indications that it cannot tolerate the use of sulphur fumigation for the control of powdery mildew.