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Aphidius-C (Aphidius colemani) - aphid parasitoid

Target pests: Green peach aphid, Myzus persicae; cotton aphid, Aphis gossypii.

Aphidius

Aphidius colemani is a small, parasitoid wasp which has been used successfully overseas for several years to control green peach aphid, Myzus persicae, and cotton aphid, Aphis gossypii. It was introduced into Australia many years ago and is naturalised.

It is also useful for other small aphids being able to parasitise over 40 species but may be less effective against certain species and in some crops. Presence of Aphidius in the colonies of some aphid species may cause them to produce an alarm pheromone, which triggers panic behaviour and dropping off the leaf, thereby avoiding parasitoids and predators, but this action of the parasites will cause many aphids to die. Parasitisation rate of larger aphids such as potato aphid, rose aphid and foxglove aphid is low. Aphidius ervi is used for these species overseas. It is present in Australia, but not commercially available, but is in our R&D program at present (2009).

Aphidius-C is supplied as parasitised aphids (mummies) in plastic vials. A minimum of 500 Aphidius wasps should emerge in each vial. Some adult wasps may emerge in transit.

Life history and biology

Aphidius-C life cycle
Click to enlarge life cycle

Aphidius colemani is a 2-3 mm long, slender, wasp with a black thorax and head and yellowish-brown legs and abdomen. The antennae are long and many-jointed. Females are more common (2:1) than males, which have a blunter abdomen. Aphidius is attracted to plants under attack and the scent of aphid honeydew. A. colemani has a very efficient searching behaviour being able to find pest aphids even at very low densities. The female wasp inserts her ovipositor into an acceptable-sized aphid by bending her abdomen forward under her body between the legs. She quickly inserts an egg into the aphid’s body cavity. She can lay up to 200 eggs during her life span. The egg swells and hatches into a legless, colourless larva. The larva grows and passes through three similar growth stages, consuming the body of the aphid from within. The aphid generally reaches an adult stage, which may be winged or wingless, before it is visibly affected. The wasp larva then attaches the body of the aphid to the leaf and spins a cocoon within the aphid, in which it pupates. The dead aphid takes on a golden brown, papery, swollen appearance, often called a ‘mummy’. It is this stage which is harvested and shipped to growers. The adult wasp cuts a neat, round hole in the upper surface of the mummy at the back to escape. The length of the life cycle is temperature-dependent, and is about 13 days at 21°C and 11 days at 27°C. The adult lives only a few days to two weeks, dependent on temperature and food supply, and needs to imbibe sugar supplied by aphids or nectar to achieve its potential.

Crop usage

Aphidius-C can be used in all crops where target aphids are pests. Crops that benefit from Aphidius-C include capsicum, tomato, cucumber, ornamentals and herbs, and some field crops such as corn and cotton.

Environmental preferences

Aphidius-C is a temperate-climate parasitoid and performs best at 18-25°C, although it is useful within a range of 15-30°C. It is not suited to temperatures <15°C or >30°C.

Application information

Storage and handling: If necessary, Aphidius-C can be stored for 24h at 6-8°C if necessary before release, but emergence and parasitisation rates may be reduced if kept longer.

Release method(s): Aphidius-C 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 at least daily by opening and tapping the vial while walking through the crop. Apply randomly through the crop if aphids have not yet been observed, or in the vicinity of aphid colonies if these are already present. Ideally, adult wasps should be released daily for 2-4 days or until no more emerge from the mummies. If this is not possible, uncap the vial and leave for a week near aphid colonies, out of direct sunlight and not exposed to overhead watering. Do not empty mummies from the vial. Ants will eat the mummies. The humidity may also be too low outside the vials for hatching.

Timing of application: Aphidius-C should be used preventatively. Releases of Aphidius-C 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. 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. Control of cotton/melon aphid is generally better than control of green peach aphid. Suggested release rates are 0.15 Aphidius/m2 weekly as a preventative treatment, increasing to 0.5–1 Aphidius/m2/week for at least 3 weeks once aphids have been detected. Control of aphids by Aphidius colemani 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 hotspots in conjunction with Aphidius.

Monitoring control success

Examine aphid colonies for 'mummies' 10-14 days after the first Aphidius-C release. Control usually follows quickly once 10% of the aphids on the leaves are clearly parasitised. Examine holes in mummies. They should be round. If the hole has a jagged edge, it may indicate the presence of hyperparasites. These are tiny wasps parasitic on Aphidius, and they are sometimes a problem in summer. Keep yellow sticky traps away from release sites as they catch Aphidius.

Tips for best results

Use preventatively, before aphids are observed in the crop, particularly in warmer months. The presence of ants attracted to aphid honeydew is a good indicator of aphid presence. Knock back any heavy infestations and reduce honeydew with compatible pesticides, even water spray, before releasing Aphidius-C. If parasitism rates are very low, have the aphid species identified. Bait ants as they are disruptive to beneficial insects.

Quality control

Batches are held and checked by Biological Services, but problems during transport may affect viability. Some parasites may emerge in transit. This is fine but check to see that these wasps are alive. If no wasps have emerged at receival hold vials until some emergence occurs and then release into the greenhouse.

Pesticide compatibility

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

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Technical resources

Aphidius technical sheet (273 kb)