Herbivore-Mediated Effects of Glucosinolates on Different Natural Enemies of a Specialist Aphid

The cabbage aphid Brevicoryne brassicae is a specialist herbivore that sequesters glucosinolates from its host plant as a defense against its predators. It is unknown to what extent parasitoids are affected by this sequestration. We investigated herbivore-mediated effects of glucosinolates on the parasitoid wasp Diaeretiella rapae and the predator Episyrphus balteatus. We reared B. brassicae on three ecotypes of Arabidopsis thaliana that differ in glucosinolate content and on one genetically transformed line with modified concentrations of aliphatic glucosinolates. We tested aphid performance and the performance and behavior of both natural enemies. We correlated this with phloem and aphid glucosinolate concentrations and emission of volatiles. Brevicoryne brassicae performance correlated positively with concentrations of both aliphatic and indole glucosinolates in the phloem. Aphids selectively sequestered glucosinolates. Glucosinolate concentration in B. brassicae correlated negatively with performance of the predator, but positively with performance of the parasitoid, possibly because the aphids with the highest glucosinolate concentrations had a higher body weight. Both natural enemies showed a positive performance-preference correlation. The predator preferred the ecotype with the lowest emission of volatile glucosinolate breakdown products in each test combination, whereas the parasitoid wasp preferred the A. thaliana ecotype with the highest emission of these volatiles. The study shows that there are differential herbivore-mediated effects of glucosinolates on a predator and a parasitoid of a specialist aphid that selectively sequesters glucosinolates from its host plant

Discovery of widespread transcription initiation at microsatellites predictable by sequence-based deep neural network

Using the Cap Analysis of Gene Expression (CAGE) technology, the FANTOM5 consortium provided one of the most comprehensive maps of transcription start sites (TSSs) in several species. Strikingly, ~72% of them could not be assigned to a specific gene and initiate at unconventional regions, outside promoters or enhancers. Here, we probe these unassigned TSSs and show that, in all species studied, a significant fraction of CAGE peaks initiate at microsatellites, also called short tandem repeats (STRs). To confirm this transcription, we develop Cap Trap RNA-seq, a technology which combines cap trapping and long read MinION sequencing. We train sequence-based deep learning models able to predict CAGE signal at STRs with high accuracy. These models unveil the importance of STR surrounding sequences not only to distinguish STR classes, but also to predict the level of transcription initiation. Importantly, genetic variants linked to human diseases are preferentially found at STRs with high transcription initiation level, supporting the biological and clinical relevance of transcription initiation at STRs. Together, our results extend the repertoire of non-coding transcription associated with DNA tandem repeats and complexify STR polymorphism

Weeds as sources of pests and natural enemies: consequences for agroecosystem management

Weeds as sources of pests and natural enemies: consequences for agroecosystem managemen

Plant neighborhood influences colonization of Brassicaceae by specialist and generalist aphids

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699International audienceA plant's own characteristics, but also those of its neighbors, might have an impact on its probability of being colonized by herbivorous insects. A plant might be less colonized and experience associational resistance when it grows near repellent neighbors. In contrast, it might be more colonized and experience associational susceptibility near attractive neighbors. To date, mechanisms that drive associational defense are not really understood. In order to gain insights into the occurrence of associational resistance versus associational susceptibility under field conditions, we conducted an experiment to determine the influence of neighboring plants on the colonization of a focal plant by aphids. The focal plant was always Brassica oleracea. The neighbors were B. oleracea (control), B. napus, B. nigra, or Solanum lycopersicum, which represent contrasting levels of physical and chemical defenses. The focal plant, B. oleracea, was more colonized by the specialist aphid Brevicoryne brassicae, and experienced associational susceptibility when it was surrounded by B. nigra or B. napus. In contrast, B. oleracea was less colonized by the generalist aphid Myzus persicae, and experienced associational resistance when it was surrounded by S. lycopersicum, B. nigra or B. napus. Neighboring plants had no significant impact on host plant choice by the generalist aphid Macrosiphum euphorbiae. In conclusion, attraction or repulsion of the specialist aphid B. brassicae and the generalist aphid M. persicae by B. nigra, B. napus, and S. lycopersicum resulted in associational susceptibility or associational resistance for B. oleracea

Puis-je compter sur mes voisins pour me défendre?

Puis-je compter sur mes voisins pour me défendre

Performance of an aphid Myzus persicae and its parasitoid Diaeretiella rapae on wild and cultivated Brassicaceae

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699To determine to what extent wild species related to crops might serve as refuges for insect pests and their natural enemies, we compared the performance of the aphid Myzus persicae and its endoparasitoid Diaeretiella rapae on one cultivar of Brassica napus and Brassica oleracea, two wild species Brassica nigra and Sinapis arvensis, and one cultivar of Solanum lycopersicum. These species differ in traits associated with plant defences that may have an impact on the herbivore and its parasitoid. In contrast to our initial hypothesis, aphid population growth rate was significantly smaller on B. napus than on the other Brassicaceae species. Similarly, the performance of the parasitoid was affected by the host plant on which the aphid was feeding. However, aphid and parasitoid performance was not correlated. Thus, in temporally changing landscapes, pests and natural enemies may utilize crops and wild-related host species with contrasting impacts on their fitness

Plant-mediated effects on a toxin-sequestering aphid and its endoparasitoid

Variation in plant morphology and chemistry can directly influence the performance of insect herbivores. A growing number of studies indicate that plants can also influence the performance of the natural enemies of the herbivores. Plant species in the Brassicaceae produce secondary compounds known as glucosinolates (GLS) whose hydrolysis products are potentially toxic to many herbivores. Some specialist insects are known to sequester the GLS, but up to date, there is no data on impact of GLS sequestration by insect herbivores on the performance of their parasitoids. We asked whether the performance of the GLS-sequestering aphid Brevicoryne brassicae and its parasitoid Diaeretiella rapae were affected by the host plants on which they feed. We selected four host plant species, one cultivar of Brassica oleracea and B. napus, and two wild species, B. nigra and Sinapis arvensis. Among other traits, these species differ in GLS content and composition as well as in some morphological characteristics. Population growth rate of Br brassicae was not affected by host plant species. However, adult aphids were the smallest, but also lived the longest when they had developed on the B. oleracea cultivar. Parasitoids were larger when their aphid hosts fed on the wild species. Unexpectedly, parasitism rate was lower on B. oleracea. Thus, variation in host plant characteristics had an impact on the fitness of the parasitoid through its aphid host. In contrast to previous studies, which have shown that sequestration is a good defence mechanism against predators, we did not observe that Br brassicae benefits from the sequestration of GLS to limit attacks by its main parasitoid

The genome sequence of the grape phylloxera provides insights into the evolution, adaptation, and invasion routes of an iconic pest (vol 18, 90, 2020)

An amendment to this paper has been published and can be accessed via the original article