Aphid control

Aphiline c

Aphidius colemani

 

How does it work?

Aphidius colemani females seek out and parasitise aphids. The most frequent host and main target is Aphis gossypii, the Melon or Cotton Aphid, but Myzus persicae, the Peach-Potato Aphid is also controlled by this parasitoid. Insecticide resistant strains are also controlled. The Bird Cherry aphid Rhopalosiphum padi is also attacked and is routinely used on ‘banker plants’ as an alternative host for the parasitoid. Many other aphid species are reported as hosts, but less information is available about these.

Once a female finds an individual aphid or aphid colony, she will palpate the aphids with her antennae. If the aphid she is examining is of the correct size, and has not already been parasitised, she rapidly curls her abdomen under her body and stabs the aphid with her ovipositor. This takes less than one second, but in this time the female checks the identity of the aphid with her ovipositor and lays an egg into it if she is satisfied. The egg soon hatches, and the resulting larva begins to feed within the aphid. Initially it will not kill the host, but as it grows it begins to feed on the vital organs so that the aphid dies. When fully grown, the Aphidius larva cuts a slit in the hollowed out shell of its host, and attaches the carcass to the substrate with silk. As it spins more silk within the host skin, this gradually takes on a golden colour and forms the characteristic ‘aphid mummy’. Within the mummy, the larva pupates, and after four or five days an adult is ready to emerge. This adult cuts a circular trap door in the mummy, always on the upper surface at the back, and escapes through this to seek fresh hosts.

 

When and where should you use it?

Aphiline c can be used either as a preventive treatment to protect the crop against attack by the aphids Aphis gossypii and Myzus persicae, or as a corrective treatment when colonies of these aphids are found.

In the first case, it is possible to make a low rate (for example 0.1-0.5/m²) release weekly during the period when aphids are most likely to arrive in the crop, usually in the spring or early summer. The first aphids to arrive are located and attacked by the parasites, and this can entirely prevent the development of colonies in some cases. Where this does not occur the growth of the colony is slowed, giving the grower more time to locate it and take further action to limit its expansion.

Where colonies are already present, the product may be used correctively at a much higher rate, generally by releasing the parasites immediately adjacent to the colonies. The adult females will quickly locate and attack the aphids. Where no previous releases have been made, the aphid population may grow very rapidly (up to 20 times in one week for some species), even after release of the parasitoids. It may take several generations for control to be achieved, and some alternative control method may be appropriate. There are several insecticide treatments that are compatible with Aphidius.

If aphid populations are already well established or the crop is extremely sensitive, for example because of the risk of virus transmission, then an immediate treatment with a compatible insecticide offers the best option for control. Aphiline c can continue to be used so that aphid populations do not again become a problem.

How should you use it?

Aphiline c will be delivered in a vial containing a mixture of mummies and freshly emerged adults. To use the product preventively, simply hold the container horizontally and gently unscrew the cap whilst standing in the crop.

Walk amongst the crop, allowing the emerged adults to fly out as you do so. Place the vial with remaining unhatched mummies horizontally in a shaded position amongst foliage for the rest of the wasps to emerge. Recap the bottle and store at greenhouse temperature until more adults have hatched. Repeat the distribution of adults daily for 2-4 days until most adults have emerged from the mixture. Finish by placing the open tube in the greenhouse next to a plant in case more hatch. Do not empty the mummies out of the tube, as this reduces the humidity around them and results in poor emergence. Make sure that the tube is clear of irrigation lines or other sources of liquid. For corrective use, open the vials immediately next to identified colonies to allow the adults to escape. Leave the vial with the remaining unhatched mummies at the base of the affected plant.

Banker plants, which have a small population of Aphidius colemani breeding on a cereal aphid, are available in some countries. These provide an alternative method of releasing low numbers of the parasite, but require horticultural care.

When should you not use it?

Aphiline c contains the parasitoid Aphidius colemani, which is known to be effective for control of Aphis gossypii, Myzus persicae and Myzus nicotianae. It will also parasitise some other species of aphids, but is not effective against Macrosiphum species. Always identify the aphid before using the product.

In the case of very high aphid populations, or a severe risk of virus damage, use a compatible aphicide to reduce the aphid population before attempting to use Aphiline c. Compatible compounds include pymetrozine, pirimicarb and neonicotinoid insecticides applied through the irrigation system. (Product registration varies from country to country. Always check that the product is available on the specific crop being treated).

Syngenta Bioline also produces the aphid parasitoids Aphelinus abdominalis and Aphidius ervi, which are effective against other aphid species. The three parasitoids are available as a mixed product, Aphiline ACE mix, for use when more than one species of aphid is present.

High summer temperatures may reduce the efficacy of Aphidius colemani. Monitor the crop closely during hot weather.

 

What will it do?

When used as recommended, Aphiline c will prevent populations of the named aphids from developing, or will reduce moderate populations to non-damaging levels. The parasite Aphidius colemani is capable of eradicating some aphid populations over several generations, and may then disappear from the crop. If this is the case then it may be necessary to reintroduce it to prevent problems from fresh aphid invasions.

 

What will it not do, and what are the control options?

Aphidius colemani will not parasitise Macrosiphum spp., and should not be used where this is the pest species. Aphidius colemani will eventually control even large populations of susceptible aphids, but may take several generations to do so, during which time aphid damage may exceed acceptable levels. For heavy infestations therefore, consider using a compatible insecticide or an alternative biological control such as larvae of Chrysoperla carnea, (or C. rufilabris in North America), or Adalia bipunctata. The fungal pathogens Verticillium lecani and Beauveria bassiana may also be available for aphid control in some countries.

For the aphid species Macrosiphum euphorbiae and other large aphids, use the alternative parasitoids Aphelinus abdominalis or Aphidius ervi, or the predatory midge Aphidoletes aphidimyza.

 

Chemical compatibility.

A number of insecticides for aphid control are compatible with the use of Aphidius.

Products that which kill the host aphid, will inevitably reduce parasitoid populations by killing hosts containing parasite larvae, but Aphidius pupae within mummies may survive. Avoid the use of insecticides between release of Aphidius and mummy formation on the plants.

Note: Hyper parasitism.

Aphidius spp. are subject to hyper-parasitism during the summer months. In regions where hyper-parasites are common, this can influence the success of aphid control. Mummies from which hyper-parasites have emerged can be recognised by the jagged emergence hole, which is usually on the side of the mummy. This is quite distinctly different from the circular emergence hole cut by Aphidius spp.

Syngenta Bioline produce Aphidius in compartments designed to exclude hyper-parasites..