126 research outputs found
Des odeurs pour protéger les cultures (utilisation de composés volatils pour modifier le comportement de la mouche du chou, Delia radicum et de ses ennemis naturels)
Les recherches menĂ©es au cours des derniĂšres annĂ©es ont permis de mettre en Ă©vidence les nombreuses fonctions Ă©cologiques des composĂ©s organiques volatils (COVs) Ă©mis par les plantes. Cette thĂšse a eu pour objectif d'utiliser ces connaissances dans un cadre de protection des cultures. Nous avons essayĂ© de poser les bases d'une stratĂ©gie de type Push-Pull contre la mouche du chou (Delia radicum) en utilisant des sources d'odeurs synthĂ©tiques (diffuseurs de COVs) ou des sources d'odeurs naturelles (plantes compagnes). A partir d'observations menĂ©es en plein champ nous avons sĂ©lectionnĂ© plusieurs brassicacĂ©es prĂ©sentant des taux d'infestations contrastĂ©s vis-Ă -vis de la mouche du chou. Des expĂ©rimentations de laboratoires combinant des Ă©tudes comportementales et des analyses chromatographiques ont permis (i) d'Ă©tablir un lien entre l'infestation et l'attractivitĂ© de certaines plantes (ii) d'identifier de nouveaux COVs potentiellement impliquĂ©s dans les prises de dĂ©cisions comportementales de D. radicum. En parallĂšle, des Ă©tudes de terrain ont permis de tester l'efficacitĂ© de diffuseurs de COVs synthĂ©tiques au sein de parcelles expĂ©rimentales, que ce soit (i) pour favoriser le recrutement d'ennemis naturels (ii) attirer (composante Pull ) ou repousser (composante Push ) la mouche du chou. Enfin, l'utilisation de plantes piĂšges concentrant le ravageur semble ĂȘtre intĂ©ressante pour modifier la rĂ©partition de la mouche du chou Ă l'Ă©chelle de la parcelle en vue de protĂ©ger des cultures d'intĂ©rĂȘt telles que le brocoli.Volatile organic compounds (VOCs) emitted by plants are used by phytophagous, predatory and parasitoid insects to adjust behavioral decisions in complex environments. We aimed at using these ecological functions of VOCs in crop protection. We developed the first steps of a "Push-Pull" strategy toward the cabbage root fly (Delia radicum) with both dispensers of synthetic VOCs and natural blends of VOCs released by plants. We conducted a field study to select brassicaceous plants exhibiting contrasted levels of infestation toward the cabbage root fly. Laboratory bioassays combining behavioral observations and gas chromatographic analyses allowed to (i) investigate the relation between plant infestation and plant attractiveness (ii) identify novel VOCs involved in behavioral decisions of the cabbage root fly. Parallel field experiments were used to test the potential of dispensers of synthetic VOCs to (i) enhance natural enemies recruitment (ii) modify cabbage root fly behavior, attracting ("Pull" component) or repelling the pest ("Push" component). Finally, we demonstrated that attractive plants are promising for a trap crop approach enabling to redistribute cabbage root fly density at the field scale in order to protect main crop such as broccoli.RENNES1-Bibl. Ă©lectronique (352382106) / SudocSudocFranceF
Patch exploitation strategies of parasitic wasps under intraspecific competition. Behav Ecol.
The optimal residence time of a forager exploiting a resource patch in the absence of competitors has been much studied since the development of the marginal value theorem. However, several foragers are frequently observed exploiting the same patch simultaneously, and patch residence time has been surprisingly little studied in such competitive situations. The few theoretical models developed on this topic predict that foragers should engage in a war of attrition and stay in the patch longer than when foraging alone. We tested this prediction in Pachycrepoideus vindemmiae (Hymenoptera: Pteromalidae), a solitary parasitoid species in which females are known to defend the hosts they are exploiting via intraspecific fighting. By measuring the effect of direct (i.e., presence of conspecifics) and indirect (i.e., presence of already-parasitized hosts) competition on patch exploitation strategies, we revealed an apparent polymorphism of strategies. Indeed, in competitive situations, some members of the population tended to retreat almost immediately from the patch whereas other members tended to remain, further exploit the patch, and be more involved in interactions with conspecifics. The proportion of ''retreaters'' strongly depended on competition intensity and prior experience of competition. The forager's physiological state (age) also affects patch exploitation strategy and the intensity of interactions between competing females. Our results highlight the necessity for further theoretical studies that consider cases where contests between foragers are costly and take into account prior experience of competition and the forager's physiological state
Plant volatiles play differential roles in pre and post alighting phases in a specialist phytophagous insect
A highâquality functional genome assembly of delia radicum L. (diptera: anthomyiidae) annotated from egg to adult
Abstract Belowground herbivores are overseen and underestimated, even though they can cause significant economic losses in agriculture. The cabbage root fly Delia radicum (Anthomyiidae) is a common pest in Brassica species, including agriculturally important crops, such as oilseed rape. The damage is caused by the larvae, which feed specifically on the taproots of Brassica plants until they pupate. The adults are abovegroundâliving generalists feeding on pollen and nectar. Female flies are attracted by chemical cues in Brassica plants for oviposition. An assembled and annotated genome can elucidate which genetic mechanisms underlie the adaptation of D . radicum to its host plants and their specific chemical defences, in particular isothiocyanates. Therefore, we assembled, annotated and analysed the D . radicum genome using a combination of different nextâgeneration sequencing and bioinformatic approaches. We assembled a chromosomeâlevel D . radicum genome using PacBio and HiâC Illumina sequence data. Combining Canu and 3DâDNA genome assembler, we constructed a 1.3 Gbp genome with an N50 of 242 Mbp and 6 pseudoâchromosomes. To annotate the assembled D . radicum genome, we combined homologyâ, transcriptomeâ and ab initioâprediction approaches. In total, we annotated 13,618 genes that were predicted by at least two approaches. We analysed egg, larval, pupal and adult transcriptomes in relation to lifeâstage specific molecular functions. This highâquality annotated genome of D . radicum is a first step to understanding the genetic mechanisms underlying host plant adaptation. As such, it will be an important resource to find novel and sustainable approaches to reduce crop losses to these pests
Impact of foliar herbivory on the development of a root-feeding insect and its parasitoid
The majority of studies exploring interactions between above- and below-ground biota have been focused on the effects of root-associated organisms on foliar herbivorous insects. This study examined the effects of foliar herbivory by Pieris brassicae L. (Lepidoptera: Pieridae) on the performance of the root herbivore Delia radicum L. (Diptera: Anthomyiidae) and its parasitoid Trybliographa rapae (Westwood) (Hymenoptera: Figitidae), mediated through a shared host plant Brassica nigra L. (Brassicaceae). In the presence of foliar herbivory, the survival of D. radicum and T. rapae decreased significantly by more than 50%. In addition, newly emerged adults of both root herbivores and parasitoids were significantly smaller on plants that had been exposed to foliar herbivory than on control plants. To determine what factor(s) may have accounted for the observed results, we examined the effects of foliar herbivory on root quantity and quality. No significant differences in root biomass were found between plants with and without shoot herbivore damage. Moreover, concentrations of nitrogen in root tissues were also unaffected by shoot damage by P. brassicae larvae. However, higher levels of indole glucosinolates were measured in roots of plants exposed to foliar herbivory, suggesting that the development of the root herbivore and its parasitoid may be, at least partly, negatively affected by increased levels of these allelochemicals in root tissues. Our results show that foliar herbivores can affect the development not only of root-feeding insects but also their natural enemies. We argue that such indirect interactions between above- and below-ground biota may play an important role in the structuring and functioning of communities
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