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Aphelinus-A (Aphelinus abdominalis) - aphid parasitoid

Target pests: Foxglove aphid/Glasshouse potato aphid, Aulacorthum solani; potato aphid, Macrosiphum euphorbiae, Green Peach Aphid (Myzus species).

Aphelinus

Aphelinus abdominalis is a small, parasitoid wasp which has been used successfully overseas for several years to control foxglove aphid, Aulacorthum solani, and potato aphid, Macrosiphum euphorbiae. It was introduced into Australia on several occasions many years ago for aiding control of bluegreen aphid and pea aphid in pastures and is now naturalised throughout the country, established on a range of aphid species.

It was commercialised in Australia in 2010 by Biological Services.

It is also useful for control of other aphids being able to feed on over 200 aphid species, and parasitises several larger species. Presence of Aphelinus in aphid colonies does not appear to disturb the aphids, even when being parasitised or fed upon. Parasitism rate of smaller aphids is generally low, but the wasps will still kill the smaller stages utilising them as a direct food source. Green peach aphid, Myzus persicae, is successfully parasitised but Aphidius colemani is still the parasitoid of choice for this pest, or both could be used in combination. Aphelinus has long-lasting but slower activity than Aphidius. Aphelinus is able to withstand higher temperatures than Aphidius.

Aphelinus-A is supplied as parasitised aphids (mummies) in plastic vials. A minimum of 1000 Aphelinus wasps should emerge from each vial. Some adult wasps may emerge in transit.

Life history and biology

Aphelinus abdominalis is a 3 mm long, stocky wasp with a black thorax and head and yellowish-brown abdomen. The antennae and legs are relatively short. Males are as common as females, but a little smaller and darker. Aphelinus is winged but seldom flies more than a short distance, preferring to walk. The female wasp checks the size of the aphid with her antennae and then backs up to the chosen aphid and inserts her ovipositor into older nymphs or even adult aphids. The aphid does not appear to be disturbed by this activity, which can take a minute or more. Female wasps can lay several hundred eggs in batches of 10-15/day for several weeks, starting 3-4 days after emergence. The eggs hatch into  legless, colourless larva inside the aphid body. The larva grows and passes through three similar growth stages, consuming the body of the aphid from within. The aphid generally reaches the adult stage, which may be winged or wingless, before it is visibly affected. After about 2-3 weeks, the aphid turns black and is mummified. It is this stage which is harvested and shipped to growers. Two weeks after mummies are formed, the adult wasp cuts a jagged, round hole in the upper surface of the aphid abdomen to escape. The length of the life cycle is temperature-dependent, and is about 3 weeks at an average of 20°C and faster at warmer temperatures. The adult is long lived, much longer than Aphidius, and obtains energy for egg laying by feeding directly on smaller aphids, and aphid stages which have not been parasitised.

Crop usage

Aphelinus-A can be used in all crops where target aphids are pests. Crops that benefit from Aphelinus-A include vegetables (capsicum, eggplant, tomatoes, lettuce), ornamentals (gerbera, chrysanthemum, rose), strawberry and herbs.

Environmental preferences

Aphelinus-A is a warm-temperate parasitoid and performs best at 20-28°C, although it is useful within a range of 15-32°C. It is not suited to temperatures <15°C or >32°C, but will survive at temperatures around 36°C provided it is not constant. They are more suited than Aphidius to hotter temperatures.

Application information

Storage and handling: Aphelinus-A can be stored for a few days at 8-10°C if necessary but emergence and parasitisation rates may be reduced if kept longer.

Release method(s): Aphelinus-A should be held in vials at room temperature (20-24°C), out of direct sunlight, until some adult wasps emerge. These should then be released daily by opening and tapping the vial while walking through the crop. Apply evenly through the crop if aphids have not yet been observed, or in close proximity to aphid colonies if these are already present. Ideally, adult wasps should be released daily until no more emerge from the mummies. If this is not possible, uncap the vial and leave horizontally for a week near aphid colonies, out of direct sunlight and not exposed to overhead watering. Do not empty mummies from the vial. Ensure that ants are controlled in the release areas as ants can eat the mummies prior to the wasps emerging.

Timing of application: Aphelinus-A should be used preventatively to help stop aphid colony build-up. Releases are best made weekly in susceptible crops prior to aphids invading, or at the very first sign of aphids. They should continue to be released until they are well established on any pest populations in the crop. Note it may take 3-4 weeks following first releases before black mummies are visible. Yellow sticky traps are not a good indicator of aphid infestation levels in the crop, although they may indicate a major flight of winged aphids entering the greenhouse.

Release rates: Release rates will vary depending on the species of aphid being targeted, the attractiveness of the crop, and the temperature of the greenhouse. Suggested release rates are 0.5-2 Aphelinus/m2 weekly as a preventative treatment, increasing to 2-4/m2/week for at least 3 weeks once aphids have been detected. Control of aphids by Aphelinus abdominalis is not immediate, therefore, spot-treatment of aphids in hot-spots with a low toxicity, short-residual pesticide is recommended to prevent migration of winged adults through the greenhouse. An aphid predator such as brown lacewing, green lacewing or ladybeetles can also be helpful in aphid hot-spots in conjunction with Aphelinus and Aphidius.

Monitoring control success

Examine aphid colonies for black 'mummies' 3 weeks after the first Aphelinus-A release. Emergence holes in the mummy should follow in another 1-2 weeks. Holes should be round with a somewhat jagged edge and indicate emergence of the next generation of wasps. Keep yellow sticky traps away from release sites as they catch Aphelinus. Dead aphids may indicate host feeding.

Tips for best results

Use preventatively, before aphids are observed in the crop, particularly in warmer months. Mobility of Aphelinus is low, so release very close to aphid colonies where these are present. The presence of ants attracted to aphid honeydew can be an indicator of aphid presence. Knock back any heavy infestations and reduce honeydew with compatible pesticides, even a pressurized water spray, before releasing Aphelinus-A. If parasitism rates are very low, have the aphid species identified. Bait ants as they are disruptive to all beneficial insects.

Quality control

Batches are held and checked by Biological Services, but problems during transport may affect viability. Mummies are shipped close to emergence time, so some parasitoids may emerge in transit. Check that these wasps are alive. Dead wasps may indicate unsuitable conditions in transit. If no wasps have emerged at receipt, hold vials until some emergence occurs and then release wasps into the greenhouse. This should occur within 2-3 days after receival, but may take longer in cold conditions. Report any failure to emerge.

Pesticide compatibility

Adult Aphelinus abdominalis are generally less sensitive to pesticides than Aphidius colemani but always check side-effects data before applying any pesticides. Aphelinus stages in mummies are more resistant to pesticides than adults but may be affected in early development. There may be differences in sensitivity to specific pesticides between European and Australian Aphelinus abdominalis so caution is advised.

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Technical resources

Aphelinus technical sheet (140 kb)