Budworm pests and parasitoids

The parasitoid species attacking grapevine moths are very numerous (figure 1), but are not specific to these hosts and their action varies from one season to another, according to the plots and according to the wine-growing regions. It is the pre-imaginal stages of fruit moths (eggs, larvae) that can be parasitized. These auxiliaries play a great importance in the regulation of populations of these pests in the vineyard. Most of the parasitoids currently present in vines already existed more than a century ago.

Four main groups of parasitoid helpers can be cited:

• the Hymenoptera Trichogrammatidae which parasitize the eggs;
• the ichneumonid hymenoptera (Ichneumonidae, Braconidae) parasitizing caterpillars and pupae;
• the chalcidian hymenoptera (Pteromalidae, Eulophidae) which parasitize caterpillars;
• Diptera Tachinidae which also parasitize caterpillars.

The maximum effectiveness of parasitism observed in the vineyard varies according to the parasitoids, the wine-growing regions as well as the vine varieties: 30 to 40% for trichogramma (release of biological control), 70 to 80% for ichneumonids, 20 to 25% for tachinids and pteromalids. Parasitism is mainly cyclical and a function of the level of presence of the budworms, the presence of alternative hosts and the adjacent vegetation for the food of the adults of the parasitoids. It is also very dependent on abiotic conditions; temperature and humidity allowing or not the survival of the parasitoid. In addition, the grape variety as a source of food for the budworm caterpillar modulates its immune system, allowing it to more or less resist parasitism.

• Trichogrammatidae

Trichogrammae are very small (0.3 to 1.2 mm) hymenoptera, with bent antennae and forewings with a single vein (Figure 2). These parasitoids lay only in eggs. The rate of natural parasitism in cochylis or eudemias may sometimes be greater than 50%. The budworm eggs then turn charcoal gray. These auxiliaries are widely used in biological control in crops, but not on a large scale in the vineyard. Only a few species are reared in commercial production ( T. cacoeciae, T. brassicae , and T. minutum ). The systematics of trichogramma is complex, the species are determined either by morphological identification, but the help of molecular biology becomes necessary to avoid confusion.

• Ichneumonidae

Hymenoptera of this family are characterized by filiform antennae of at least 16 articles and the anterior edge of the forewing which is thickened with a conspicuous stigma. The female auger is often very long. These insects are abundant in hedges and can be recognized by the vibration of their antennae looking for a host that can be detected by its scent.

In this family, several species are important parasites (eg Campoplex capitator and Exochus tibialis which are found quite frequently). Campoplex capitator Aubert 1960 (formerly C. majalis , Campopleginae, figure 3), is a solitary endoparasite and is the species most often found in European vines. It is 5 to 6 mm long, and can be recognized by its completely black body except for the femurs and tibias which are reddish brown. Eudemis and cochylis are its two main hosts. The female lays eggs in the second to fourth instar larvae and the larva leaves its host after pupation. She then weaves a white cocoon from which the adult emerges about a week later in summer (figure 3). Campoplex capitator is active throughout the season, and may diapause in pupae of diapausing cluster worms.

Diadegma fenestrale (Holmgren, 1860) (Campopleginae, figure 4) is a very polyphagous auxiliary, and a major parasitoid of the corn borer . This species provides 60 to 70% of the parasitism of this pest, and also participates in the control of eudemias and cochylis .

• Braconidae

This family is one of the most important families of Hymenoptera with several thousand species, all parasitoids of insects (mainly Coleoptera and Lepidoptera). Some sub-families are very specialized. The identification of Braconidae is delicate; very similar to the Ichneumonidae, we can differentiate them by the different venation of the fore wing ( see here ). Their size varies from 1 to 10 mm, ie they are generally smaller than the Ichneumonidae. Their ovipositor is usually visible but sometimes inconspicuous.

Apanteles sicarius Marshall 1885 (Microgastrinae) parasitizes the corn borer . The insect's body measures 2.5 to 3 mm, is shiny black with yellow stained legs at the end. The female lays eggs in the young caterpillars then the larva leaves its host to weave a pupation cocoon attached to the leaf by bristles (figure 5). These are the first cocoons visible in the vineyard. This parasitoid, very widespread in Europe, is not specific and attacks many species of phytophagous caterpillars.

• Pteromalidae, Eulophidae
  

Pteromalids are Chalcidoidea hymenoptera often small (a few mm), often metallic in color, with a very reduced wing vein and bent antennae of 3 to 8 sections (figure 6). Females lay several dozen eggs on the host's cuticle. The larvae of the parasitoid (ectoparasite) will devour the caterpillar from the outside. Two species have been recognized on Tortricidae of the grapevine of the genus Dibrachys ( D. cavus and D. affinis ). These two species are involved in the late summer generation, having a non-negligible regulatory role on the overwintering generation. The female lays eggs on the chrysalis which will produce 6 to 14 adult parasitoids.

Eulophids are Hymenoptera Chalcidoidea, whose tarsi are 4-segmented, antennae 7-9 segmented, and the gastre distinctly petiolate. Colpoclypeus florus (Walker, 1839) is a major gregarious ectoparasitoid of eulia , but this species is also highly polyphagous.

• Tachinidae

The adults of this Diptera family are floricultural (Figure 7). Some species lay their eggs on the foliage and these will then be eaten by the budworm caterpillar, others lay on or in the host. One to five larvae develop in it. At the end of their development, the larvae leave their host and pupate near or in the soil. Parasitism is very effective against Lepidoptera: Noctuidae, Geometridae, Tortricidae and Pyralidae as well as Crambidae.

Among several species of tachinids occasionally encountered on grapevine budworms, two should be noted: Phytomyptera nigrina and Pseudoperichaeta nigrolineata . The latter is reported to parasitize more than 50 species of caterpillars. The female lays her egg on the host's integument and upon hatching, the larva enters it. The first species is less generalist and therefore more interesting in the vineyard, it preferentially parasitizes cochylis and eudémis . In the first generation of eudemias , the parasitism can be from 10 to 25%. This species is multivoltine.

Bibliography

Delbac L (2014) Meeting Eudémis SudvinBio, CRA Languedoc Roussillon ( pdf )

Thiéry D (2008) Budworm harmful to vines. in: Vine pests, Esmenjaud et al., Ed Feret

Thiéry D, Yoshida T, Guisset M (2006)  Phytomyptera nigrina  (Meigen), a parasite of first generation European grapevine moth larvae in several vineyards in the Roussillon area.  The Tachinid Times , 19, 1-4 ( pdf )

Thiéry, D., Louâpre, P., Muneret, L., Rusch, A., Sentenac, G., Vogelweith, F, Iltis, C., Moreau, J. (2018) Biological protection against grape berry moths: A review. Agronomy for Sustainable Development, 38, 1-18.  doi.org/10.1007/s13593-018-0493-7

Villemant C, Sentenac G (2013) Parasitoids of grape berry moths. Specific diversity and biology. Seminario Biodiversidade em viticultura, Lisbon Portugal November 4-5, 2013 ( pdf )

Villemant C, Delvare G, Martinez M, Sentenac G, Kuntzmann P (2011) Budworm parasitoids. In: Auxiliary fauna of the vineyards of France, Eds France Agricole-Dunod

Universal Chalcidoidea Database - Notes on families. Site web du Natural History Museum