Often invisible but very effective: parasitoids

What is a parasitoid?

This term was created to differentiate various types of parasitism because parasitoids are parasites of parasites, and it was necessary to be able to differentiate them in everyday language. In general, they are insects that develop inside another insect, a parasite of our plants. It develops at the same time as its host but kills it before it can reproduce, hence its preventive effectiveness.

In which situations are they very useful?

In our crops, they are mainly used to control aphid attacks, but they are also interesting against whiteflies or mealybugs in the greenhouse.
In field crops they have been used for many years against the corn borer (trichogramma).
In addition, research in the field of Integrated Biological Protection (PBI) researches and makes it possible to broaden the spectrum of parasites combated by this technique.
We can cite for example:

_· _Against fruit fly suzuki the recent marketing of Trichopria drosophilae.

· Against the codling moth of apples, pears, and nuts, a non-indigenous braconid insect is in the large-scale study phase with INRAE: Mastrus lines.

· New, a parasitoid to fight against the green bug, Nezara viridula which is beginning to do significant damage in our vegetable gardens, especially on tomatoes: Trissolcus basalis. New to test but a bit expensive to buy (€97.50 excluding tax for 500 insects).
These last three new ones represent a very important hope because of the damage that the targeted parasites do.

How are they marketed?

Most of the time they are marketed as pupae as this is the stage of development where they support transport. The pupae are installed near or in the crops to be protected, often with a supply of food (honey and pollen). So when the adults hatch, fertilization takes place and the females go directly in search of prey. The food brought on site keeps the females on the site.

Pros and cons:

Most :

· This type of auxiliary acts over the long term because it follows the rhythm of life of its host. So he stays there for a long time.
· It is used in a preventive way thus avoids the peaks of parasitisms.

The lessers :

· As they live inside a host, the grower must precisely identify the species being controlled. But currently there are packaging on the market containing several species of parasitoids adapted to many species of aphids, making it possible to circumvent misidentifications.
· Their action lags behind release due to the time it takes for pupae to become adults and for eggs to hatch in hosts. But it is also an advantage in preventive action.
· These parasitoids are very small and have fairly weak flight abilities and can therefore only move over short distances (a few meters).

Some interesting species:

In parasitoids the size of the host is of great importance, which is why breeding laboratories offer mixes of several species for the fight against aphids.
Aphidius colemani: small aphids, gives rather pale, beige mummies

Aphidius ervi: large aphids, gives darker, brown mummies with sometimes a coppery appearance.
Aphidius matricariae: aphids can parasitize 40 species of aphids. Gives somewhat copper colored mummies
Aphelinus abdominalis: aphids, he is from the family of Aphelinidaewith an advantage because oviposition in the aphid is slower but shows much higher success rates than for the Braconidae (braconids).

Praon volucre: aphids, has a particularity that aphids parasitized by this braconid because the larva has part of its body outside the aphid, the head being inside. This parasitoid creates a kind of membranous skirt under its host when transforming.
This auxiliary has another peculiarity, it only lays eggs in small colonies of aphids. It is an auxiliary of the beginning of attack.

Metaphycus: lecanine mealybugs,
Coccophagus: mealybugs,
Diglyphus iseae : Interesting parasitoid to control leaf miners (sorrel).
Encarsia formosa: Whiteflies, rather in greenhouse.
Eretmocerus eremicus: Whiteflies,

Neodryinus typhlocybae: Against the pruinose leafhopper, metcalfa pruinosa, of fairly recent use (early 2000s) its early release in the city of Grenoble has made it possible to seriously limit the establishment of the pruinous leafhopper in the Grenoble region, unlike, for example, in the neighboring department of Drôme which has been very affected by the parasite.
But this auxiliary has some flaws, it is very slow to install. It is very sensitive to all insecticides, including organic ones. Was only distributed by the Corsican FREDON because it is not high in the laboratory.

Torymus sinensis: chestnut gall wasp, Dryocosmus kuriphilus chestnut gall maker, Like Neodryinus, it is not raised in the laboratory. It is necessary to take galls from trees in areas where the parasitoid is present and put these galls in breeding while waiting for the emergence of the imago. It is therefore not marketed, but was released a few years ago by the FREDONs in areas where there are many chestnut trees (Anjou, Ardèche).

Ask all your questions during the gardening program on Sunday morning on France bleu Isère from 9 a.m. to 10 a.m. by calling 04 76 46 45 45.