Aider à la gestion des services de régulation naturelle des bioagresseurs : enjeux de connaissances et de prise en compte des agriculteurs : une approche bibliographique

Comment construire des connaissances pour aider les agriculteurs à mieux mobiliser les services de régulation naturelle des bioagresseurs? Nous avons réalisé une revue de la littérature scientifique pour examiner si et comment les connaissances produites pouvaient aider à la réalisation d'un diagnostic de ces services. Nous avons considéré pour cela que ces connaissances devaient porter sur les relations entre i) la problématique de la régulation naturelle des bioagresseurs, ii) les facteurs affectant cette problématique (e.g., pratiques agricoles, environnement paysager), et iii) les ressources des agriculteurs impactées par la régulation biologique (e.g., productions) et/ou permettant de maîtriser les facteurs affectant cette régulation (e.g., ressources en connaissance, travail, équipements). Nous avons aussi examiné si les dynamiques temporelles de ces relations étaient étudiées (Duru, Therond et al, 2015). 1. Nous avons réalisé une requête large dans le Web Of Science des études portant sur le contrôle, y compris chimique et/ou mécanique, des bioagresseurs (15334 articles). 2. Ayant peu de mots clés précis pour identifier les dimensions d'un diagnostic dans ces études, nous avons construit et mobilisé des dictionnaires de mots clés dans une analyse lexicale de notices avec l'outil CorText. Un sous-corpus de 6024 articles a été obtenu après extraction d'études hors-sujet. Nous avons identifié 9 thématiques diversement combinées dans les études, les plus fréquentes étant: "gestion des bioagresseurs", "gestion des adventices", "systèmes de cultures", "modélisation et prise de décision", "acteurs et système d'exploitation" et "agroécosystème et paysage". 3. Afin d'identifier les connaissances utiles pour un diagnostic à partir de ces thématiques, nous avons échantillonné des études selon leurs profils et les avons analysées à partir d'une grille de lecture ad hoc. Nous présentons les résultats pour une sélection de 31 études les plus pertinentes a priori. Leurs notices mentionnent la régulation naturelle des bioagresseurs et combinent 3-5 thématiques dont au moins "acteurs et systèmes d'exploitation": notre hypothèse est qu'elles prennent en compte explicitement les acteurs et leurs ressources. Ces études sont effectivement les plus riches. Cependant la plupart n'étudient aucune dynamique temporelle. Nous avons distingué 3 groupes. Le premier groupe (15 articles) met l'accent sur l'élucidation de l'influence relative des facteurs "pratiques" et "paysage" sur le phénomène de régulation; les ressources des agriculteurs sont contextuelles (ex: comparaison agriculture biologique vs. agriculture conventionnelle). Le deuxième groupe (6 articles) met l'accent sur l'impact de la régulation biologique et/ou des nouvelles pratiques et aménagements paysagers sur les ressources des agriculteurs (e.g., coûts/bénéfices économiques) à l'échelle de la parcelle. Le dernier groupe (10 articles) est le plus intégrateur des composantes du diagnostic; on y trouve le plus d'études engagée dans l'accompagnement des agriculteurs, notamment l'apprentissage collectif (Bell et al, 2016; Robertson et al, 2014)

The Chalcidoidea bush of life: evolutionary history of a massive radiation of minute wasps.

Chalcidoidea are mostly parasitoid wasps that include as many as 500 000 estimated species. Capturing phylogenetic signal from such a massive radiation can be daunting. Chalcidoidea is an excellent example of a hyperdiverse group that has remained recalcitrant to phylogenetic resolution. We combined 1007 exons obtained with Anchored Hybrid Enrichment with 1048 ultra-conserved elements (UCEs) for 433 taxa including all extant families, >95% of all subfamilies, and 356 genera chosen to represent the vast diversity of the superfamily. Going back and forth between the molecular results and our collective knowledge of morphology and biology, we detected bias in the analyses that was driven by the saturation of nucleotide data. Our final results are based on a concatenated analysis of the least saturated exons and UCE datasets (2054 loci, 284 106 sites). Our analyses support an expected sister relationship with Mymarommatoidea. Seven previously recognized families were not monophyletic, so support for a new classification is discussed. Natural history in some cases would appear to be more informative than morphology, as illustrated by the elucidation of a clade of plant gall associates and a clade of taxa with planidial first-instar larvae. The phylogeny suggests a transition from smaller soft-bodied wasps to larger and more heavily sclerotized wasps, with egg parasitism as potentially ancestral for the entire superfamily. Deep divergences in Chalcidoidea coincide with an increase in insect families in the fossil record, and an early shift to phytophagy corresponds with the beginning of the "Angiosperm Terrestrial Revolution". Our dating analyses suggest a middle Jurassic origin of 174 Ma (167.3-180.5 Ma) and a crown age of 162.2 Ma (153.9-169.8 Ma) for Chalcidoidea. During the Cretaceous, Chalcidoidea may have undergone a rapid radiation in southern Gondwana with subsequent dispersals to the Northern Hemisphere. This scenario is discussed with regard to knowledge about the host taxa of chalcid wasps, their fossil record and Earth's palaeogeographic history

Vectors of Xylella fastidiosa show pronounced habitat preferences in Corsican agricultural landscapes

International audienceIn Europe, many potential and confirmed vectors of Xylella fastidiosa (Xf) are polyphagous but appear to aggregate on their preferred host plants at local scales. For example, Philaenus spumarius is found most often on Asteraceae on the Californian coast, or on Apiaceae and Rubiaceae in the meadows of central Italy. However, vectors keep the ability to exploit multiple host-plants, which can be crucial in primary Xf transmission to crops.In this study, we assessed the habitat preferences of spittlebugs on and in the vicinity of Corsican clementine and olive groves, focusing on four habitats: Cistus monspeliensis border, Dittrichia viscosa cover, crop foliage and grove ground vegetation. Spittlebug abundance was assessed three times a year during two years on five to nine clementine and olive organic groves. Nymph and adult abundances were quantified based on spittle mass counts and nymph identification in April and sweep net sampling in June and October. Habitat preferences were inferred based on generalized linear mixed models.Overall, 6647 spittle masses and 1714 adults belonging to four species were found. Philaenus spumarius had a significant preference for Cistus monspeliensis, and to a lesser extent for Dittrichia viscosa. Neophilaenus campestris mostly occurred on ground vegetation of the grove and on Dittrichia viscosa. Lepyronia coleoptrata was less abundant on crop foliage than on ground vegetation and Aphrophora alni showed an even abundance in all habitats.This study demonstrates the specialization of P. spumarius on C. monspeliensis in the diversified Corsican landscape as well as strong habitat preferences for N. campestris. All recorded species were able to colonize clementine or olive foliage, but rarely, and in similar abundancies for all species. Should they be proven equivalent effective vectors, this suggests similar roles of these four species in Xf transmission to crops

Ooctonus vulgatus (Hymenoptera, Mymaridae), a potential biocontrol agent to reduce populations of Philaenus spumarius (Hemiptera, Aphrophoridae) the main vector of Xylella fastidiosa in Europe

As a vector of Xylella fastidiosa (Wells, 1987) in Europe, the meadow spittlebug Phi-laenus spumarius (Linnaeus, 1758) (Hemiptera, Aphrophoridae) is a species of major concern. Therefore, tools and agents to control this ubiquitous insect that develops and feeds on hundreds of plant species are wanted. We conducted a field survey of P. spumarius eggs in Corsica and provide a first report of Ooctonus vulgatus Haliday, 1833 (Hymenoptera, Mymaridae) as a potential biocontrol agent of P. spumarius in Europe. To allow species identification, we summarized the main characters distinguishing O. vulgatus from other European species of Ooctonus and generated COI DNA barcodes. Parasitism rates were variable in the four localities included in the survey but could reach 69% (for an average number of eggs that hatched per locality of 109). Based on the geographic occurrences of O. vulgatus obtained from the literature, we calibrated an ecological niche model to assess its potential distribution in the Holarctic. Obviously, several questions need to be addressed to determine whether O. vulgatus could become an effective biocontrol agent of P. spumarius in Europe. So far, O. vulgatus has been reared only from P. spumarius eggs, but its exact host-range should be evaluated to ensure efficiency and avoid non-target effect. The top-down impact of the parasitoid on vector populations should also be assessed on large data sets. Finally, the feasibility of mass rearing should be tested. We hope this report serves as a starting point to initiate research on this parasitoid wasp to assess whether it could contribute to reduce the spread and impact of X. fastidiosa in Europe

Xylella fastidiosa : Retours sur la deuxième conférence européenne

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Wanted egg parasitoids: Ooctonus vulgatus parasitizes Philaenus spumarius in Corsica and is probably widely distributed in Europe

International audienceCurrent management of Xylella fastidiosa (Xf) epidemics worldwide predominantly involves plant uprooting, soil tillage or insecticide use. Improving vector biological control may be an interesting environmentally friendly lever to help lower vector density, but this research field has been overlooked until very recently.Three types of natural enemies of Philaenus spumarius have been described: egg parasitoids, larval and adult predators, and adult parasitoids. In the present study, we tried to identify egg parasitoids of P. spumarius in Corsica and to give a first assessment of their efficiency in natura. For that purpose, we collected bunches of branches of Cistus monspeliensis in winter, checked for the presence of eggs of P. spumarius on leaf underside, and monitored insect emergence.Ooctonus vulgatus Haliday, 1833 was identified by morphological and molecular methods as emerging from 255 P. spumarius eggs, out of 808 emerged individuals (total sample size = 1107 eggs). This was the only parasitoid species found and it was recorded on 7 out of 9 sampling sites, with parasitism rates ranging from 4 to 69 %. Species distribution models fitted on all available occurrences of O. vulgatus worldwide show that this species is likely to be found commonly in northwestern Europe.Among known natural enemies of P. spumarius, egg parasitoids have a unique combination of features: they kill the pest before it reaches the most harmful stage, and usually exhibit a high level of host specialization. Consequently, we can expect that spatially restricted mass releases in host habitats could decrease Xf transmission without side effects on the local fauna. Egg parasitoids are promising biocontrol agents for the Xf vectors and, provided that we gain more information on their level of specialization and establish mass-rearings, they can be a tool of an IPM strategy for the management of the Xf pathosystem

Ooctonus vulgatus (Hymenoptera, Mymaridae), a potential biocontrol agent to reduce the populations of Philaenus spumarius (Hemiptera, Aphrophoridae) in Europe

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Interaction networks between spittlebugs and vegetation types in and around olive and clementine groves of Corsica; implications for the spread of Xylella fastidiosa

International audienceThe bacterium Xylella fastidiosa (Xf) is a major threat to European agriculture and notably to the olive and Citrus industry. It is transmitted by xylem-feeding insects, whose plant-feeding preferences still require investigation in European agroecosystems. Here we studied olive and clementine groves of the oriental plain of Corsica. Insect-vegetation type interaction networks for nymphs and adults of xylem-feeding insects were investigated three times a year during two years in and around crops. Networks were dominated by the Philaenus spumarius - Cistus monspeliensis interaction and were similar for olive and clementine groves, despite differences in plant communities of the ground vegetation and agricultural practices. To a lesser extent, Dittrichia viscosa was also a suitable feeding plant for P. spumarius, the main vector of Xf in Europe. Neophilaenus campestris was associated with grove ground vegetation, whereas Lepyronia coleoptrata and Aphrophora alni exhibited no or weak association with any of the target vegetation types. All species occurred on olive and clementine foliage in similar low abundance. Our results suggest that soil tillage in spring would be less efficient than in Italy to control P. spumarius. Instead, removing C. monspeliensis bushes from the close vicinity of groves could reduce risk of spread of Xf to crops. Finally, conserving D. viscosa in olive groves as a biological control strategy against the olive fruit fly is rather counter-productive as it maintains populations of P. spumarius under susceptible crops. Overall, our study shows that management strategies should be designed in relation to local insect-plant interaction networks that should be investigated in both cultivated areas and their immediate environment

Identifying the drivers of abundance of Philaenus spumarius in Corsica

International audiencePhilaenus spumarius (Hemiptera: Aphrophoridae) is a major vector of Xylella fastidiosa (Xf) in Europe. However, the drivers influencing its abundance are still poorly known. In Corsica from 2018 to 2020, we monitored the abundance of P. spumarius three times a year in 64 permanent plots distributed along vegetation and altitudinal (0-600m) gradients. The vegetation gradient ranged from shrubland to oak forest and accounted for the density of Cistus monspeliensis on which P. spumarius usually develops and feed in Corsica. Abundance of P. spumarius was estimated through visual counting of foams and sweep netting of adults. Both vegetation composition and climate descriptors were recorded at each sampling location. We used partial least squares path modelling and generalized linear mixed models to unravel the relationships between vegetation / climate descriptors and P. spumarius abundance..

Evaluer le risque associé à des agents phytopathogènes émergents transmis par des insectes : le cas de Xylella fastidiosa

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