Search results for "Aphids"
showing 10 items of 74 documents
Melatonin in the seasonal response of the aphid Acyrthosiphon pisum.
2018
Aphids display life cycles largely determined by the photoperiod. During the warm long-day seasons, most aphid species reproduce by viviparous parthenogenesis. The shortening of the photoperiod in autumn induces a switch to sexual reproduction. Males and sexual females mate to produce overwintering resistant eggs. In addition to this full life cycle (holocycle), there are anholocyclic lineages that do not respond to changes in photoperiod and reproduce continuously by parthenogenesis. The molecular or hormonal events that trigger the seasonal response (i.e., induction of the sexual phenotypes) are still unknown. Although circadian synthesis of melatonin is known to play a key role in verteb…
Natural Occurrence of Secondary Bacterial Symbionts in Aphids from Tunisia, with a Focus on Genus Hyalopterus
2018
Aphids (Hemiptera: Aphididae) can harbor two types of bacterial symbionts. In addition to the obligate endosymbiont Buchnera aphidicola Munson, Baumann and Kinsey 1991 (Enterobacteriales: Enterobacteriaceae), several facultative symbiotic bacteria, called secondary (S) symbionts, have been identified among many important pest aphid species. To determine interpopulational diversity of S-symbionts, we carried out a survey in a total of 18 populations of six aphid species collected from six localities in Tunisia, by performing a diagnostic polymerase chain reaction analysis of partial 16S-23S rRNA operon sequences. While 61.7% of individuals contained only Buchnera, three S-symbionts were foun…
Multi-modal defences in aphids offer redundant protection and increased costs likely impeding a protective mutualism.
2017
The pea aphid, Acyrthosiphon pisum, maintains extreme variation in resistance to its most common parasitoid wasp enemy, Aphidius ervi, which is sourced from two known mechanisms: protective bacterial symbionts, most commonly Hamiltonella defensa, or endogenously encoded defences. We have recently found that individual aphids may employ each defence individually, occasionally both defences together, or neither. In field populations, Hamiltonella-infected aphids are found at low to moderate frequencies and while less is known about the frequency of resistant genotypes, they show up less often than susceptible genotypes in field collections. To better understand these patterns, we sought to co…
Phylogenomics Identifies an Ancestral Burst of Gene Duplications Predating the Diversification of Aphidomorpha
2019
Aphids (Aphidoidea) are a diverse group of hemipteran insects that feed on plant phloem sap. A common finding in studies of aphid genomes is the presence of a large number of duplicated genes. However, when these duplications occurred remains unclear, partly due to the high relatedness of sequenced species. To better understand the origin of aphid duplications we sequenced and assembled the genome of Cinara cedri, an early branching lineage (Lachninae) of the Aphididae family. We performed a phylogenomic comparison of this genome with 20 other sequenced genomes, including the available genomes of five other aphids, along with the transcriptomes of two species belonging to Adelgidae (a close…
Immunity and other defenses in pea aphids, Acyrthosiphon pisum
2010
Background Recent genomic analyses of arthropod defense mechanisms suggest conservation of key elements underlying responses to pathogens, parasites and stresses. At the center of pathogen-induced immune responses are signaling pathways triggered by the recognition of fungal, bacterial and viral signatures. These pathways result in the production of response molecules, such as antimicrobial peptides and lysozymes, which degrade or destroy invaders. Using the recently sequenced genome of the pea aphid (Acyrthosiphon pisum), we conducted the first extensive annotation of the immune and stress gene repertoire of a hemipterous insect, which is phylogenetically distantly related to previously ch…
Sex versus parthenogenesis: A transcriptomic approach of photoperiod response in the model aphid Acyrthosiphon pisum (Hemiptera: Aphididae)
2007
International audience; Most aphids develop a cyclic parthenogenesis life-cycle. After several generations of viviparous parthenogenetic females, it follows a single annual generation of sexual individuals, usually in autumn, that mate and lay the sexual eggs. Shortening of photoperiod at the end of the summer is a key factor inducing the sexual response. With the survey here reported we aimed at identifying a collection of candidate genes to participate at some point in the cascade of events that lead to the sexual phenotypes. Following a suppression subtractive hybridization methodology (SSH) on the model aphid Acyrthosiphon pisum, we built and characterised two reciprocal cDNA libraries …
Molecular markers linked to breeding system differences in segregating and natural populations of the cereal aphid Rhopalosiphum padi L.
1999
The aphid Rhopalosiphum padi shows coexistence of sexual and asexual populations, providing an opportunity to study the evolution of breeding system variation in the context of theories on the origin and maintenance of sex. However, assessments of the distribution of sexual and asexual lineages of this aphid are complicated by the difficulties in rapidly characterizing their breeding system. To facilitate this task and to gain insight into the genetic relatedness between sexual and asexual genotypes, molecular markers linked to breeding system differences were recently developed. In this study, we have successfully converted a random amplified polymorphic DNA (RAPD) marker associated with l…
Species composition and richness of aphid parasitoid wasps in cotton fields in northern China
2017
AbstractThe cotton aphid, Aphis gossypii (Hemiptera: Aphididae), is a serious pest of cotton across the globe, particularly in the cotton agroecosystems of northern China. Parasitic wasps are deemed to be important natural enemies of A. gossypii, but limited information exists about their species composition, richness and seasonal dynamics in northern China. In this study, we combine sampling over a broad geographical area with intensive field trials over the course of three cropping seasons to describe parasitoid-hyperparasitoid communities in cotton crops. We delineate a speciose complex of primary parasitoids and hyperparasitoids associated with A. gossypii. Over 90% of the primary paras…
Effects of Bacillus thuringiensis δ-Endotoxins on the Pea Aphid ( Acyrthosiphon pisum )
2009
ABSTRACT Four Bacillus thuringiensis δ-endotoxins, Cry3A, Cry4Aa, Cry11Aa, and Cyt1Aa, were found to exhibit low to moderate toxicity on the pea aphid, Acyrthosiphon pisum , in terms both of mortality and growth rate. Cry1Ab was essentially nontoxic except at high rates. To demonstrate these effects, we had to use exhaustive buffer-based controls.
Phylogenetic evidence for hybrid origins of asexual lineages in an aphid species
2003
International audience; Understanding the mode of origin of asexuality is central to ongoing debates concerning the evolution and maintenance of sexual reproduction in eukaryotes. This is because it has profound consequences for patterns of genetic diversity and ecological adaptability of asexual lineages, hence on the outcome of competition with sexual relatives both in short and longer terms. Among the possible routes to asexuality, hybridization is a very common mechanism in animals and plants. Aphids present frequent transitions from their ancestral reproductive mode (cyclical parthenogenesis) to permanent asexuality, but the mode of origin of asexual lineages is generally not known bec…