Parasitic arthropods and parasitoids

A parasite is an organism that lives at the expense of another, called a host. Most entomophagous parasites are insects belonging to the Hymenoptera, Diptera and Coleoptera (see summary table, figure 1). The larvae develop at the expense of the host organism. When this one is killed after the development of the parasite is completed, these particular parasites are called parasitoids. In arthropods parasitoid , it is always the larval stages that live at the expense of a host whose death they cause, and this is how some species are used in biological control. arthropods Parasitic generally do not kill their host, but keep it alive as long as possible; rather, there is a balance between the two parties.

There are several types of parasitoids depending on their biology:

• in solitary parasitoids, a single larva develops at the expense of the host;
• in gregarious parasitoids, several larvae coexist on or in the host;
• ectoparasitoids generally consume their host from the outside, the host being sheltered in plant tissues or in a cocoon or puparium;
• in endoparasitoids, larval development takes place entirely in the host, and they must therefore be able to resist or avoid encystment by the host, for example thanks to proviruses integrated into their genetic makeup.

>>> more information on the biology of parasitoids

Economic importance of parasitoids

It is estimated that in Hymenoptera 65% of species are parasitoids; in Diptera 15% (Figures 2 and 3) and Coleoptera only 1% (Figure 7). Thus, more than 70 species of parasitoid hymenoptera have been described in the vineyard. The presence of parasitoids is, however, conditioned by cultural practices and the environment of the vineyard.

In the aculeates ( hymenoptera apocrite ), the auxiliaries are represented only by a few families of relatively minor economic importance. Some Bethylidae attack pest lepidoptera or bark beetles, while some Dryinidae have been used in biological control by introduction to control leafhoppers, for example Neodryinus typhlocybae against the plum leafhopper .

The other apocrite hymenoptera (formerly called terebrants ) are mostly auxiliaries, but a few species attack the seeds of certain higher plants. In this group of Hymenoptera, certain species can play a significant role in the natural control of certain pests of the vine, in particular in the following groups:

• the parasitoids of stinging and sap-sucking hemiptera (many Aphelinidae and Encyrtidae, Pteromalidae Eunotinae and Braconidae Aphidiinae) which regulate, often successfully, populations of whiteflies, aphids or scale insects ;
• parasitoids of flies or minor leaf microlepidoptera (certain Braconidae Alysiinae and Opiinae, certain Pteromalidae and Eulophidae);
• oophagous parasitoids ( Trichogramma ), which can exert a very important natural control and are used in biological control by flooding releases, mainly in orchards and in field crops, to control certain lepidoptera;
• Lepidoptera parasitoids are very numerous. They include first of all the oophages mentioned above, as well as a multitude of larval, larvo-nymphal or nymphal parasitoids. The most important of the first two categories (larvae and larva-nymphal) belong to the Braconidae (figures 4 and 5) and to the Ichneumonidae (figure 6).

Bibliography

Chaubet B (2018) Development cycle of a parasitoid aphid hymenoptera . Encyclop'Aphid (website on aphids, UMR IGEPP, INRA Rennes)

Delvare G (2011) The main aids in viticulture: description, ecology, biology. In: Auxiliary fauna of the vineyards of France, Eds France Agricole-Dunod

Delvare G (2020) Order Hymenoptera (Hymenoptera). In: Insects of the World: Biodiversity, Classification, Keys for determining families. Aberlenc HP, Eds Museo-Quae

Wajnberg E, Ris N (2012) Parasitism and biological control . In: Ecology and evolution of parasitic systems, Guégan JF, Renaud F, Thomas F, Eds De Boeck Supérieur