Aphids

Generalities

Aphids (order: Hemiptera) as biting-sucking insects, feed mostly on the phloem of plants and weaken the host plant by taking nutrients and/or transmitting viruses responsible for many diseases. Approximately 250 species of aphids (among 4000 listed) are important pests in agricultural or forest environments. The aphid is at the core of a network of abiotic (photoperiod, temperature) and biotic (host plant, symbiotic bacteria, natural enemies, phytoviruses, processions of food webs based on honeydew) interactions.

French research teams are studying the major biological functions that are responsible for the aphids’ high demographic and adaptive potential, such as relations with the host plant, nutrition, symbiosis, virus vectoring, interaction with natural enemies, phenotypic plasticity and reproduction mode. The development of genomics now provides a better understanding of the mechanisms behind these adaptations and interactions. Efforts made since 2003 through the International Consortium for Aphid Genomics focuses on the pea aphid Acyrthosiphon pisum, whose genome was published in 2010; other species are also being studied for the development of genomic resources.

Name : Acyrthosiphon pisum
Phylogenetic classification : phylum Arthropoda, order Hemiptera, family Aphididae
Genome sequencing: complete since 2012
Genome size : about 530 million pb on 4 chromosomes.
Number of genes : about34.000.
Trivia:
- Numerous duplicated genes with no evidence of genomic duplication ;
- Numerous examples of gene duplication/expansion associated with divergent gene evolutions ;
- Examples of loss of certain metabolic or signalling pathways ;
- Few horizontal gene transfers from the bacterial symbiote to the host aphid genome ;
- Examples of horizontal transfers of genes from other bacteria or fungi

Reproduction

Similar to all aphids, 4 larval instars follow one another during the development phase in Acyrthosiphon pisum.

There is no true metamorphosis in aphids, and the larval stages look similar to the adult stage. Breeding is carried out in laboratory on the host plant under conditions where the aphids multiply by viviparous parthenogenesis: thus it is a clone breeding. Phenotypic plasticity makes it possible to produce individuals of the same clone but with different phenotypes: winged (by increasing colony density, for example), or sexed individuals (by reducing the photoperiod). In this case, sexed fertilized females lay diapausing eggs from which new parthenogenetic individuals will emerge.

The parthenogenetic phase of the life cycle is short (about 10 days from birth to the birth of the first offspring), whereas the sexual phase lasts several months: the eggs are diapausant (more than 80 days) and the parthenogenetic colonies resulting from the spring hatching of these eggs are insensitive for several weeks to the photoperiodic changes necessary for the production of sexed individuals (founder effect).

Tools

Several natural lineages characterized on different phenotypic characteristics maintained in France, but also in the USA and Japan
RNAi by injection or feeding
ESTs and RNA-Seq libraries
DNA microarrays (24 000 genes) for transcriptomic analysis
Catalogues of small non-coding RNA (miRNA, piRNA)
Methylome data
Molecular markers for population characterization
Complete genome for several lineages of the pea aphid Acyrthosiphon pisum

Databases

Genomic ressources :

https://bipaa.genouest.org/is/aphidbase/

Metabolic networks :

http://acypicyc.cycadsys.org/

Phylogenomics :

http://www.phylomedb.org/phylome_16

Infrastructures

Experts

Bibliography

Articles about genomics are listed on the web tool Aphidbase : https://bipaa.genouest.org/is/aphidbase/