Aphids are important agricultural pests that have alternate life cycle from parthenogenetic to sexual generations. They are small, soft-bodied insects that feed exclusively on plant phloem sap by inserting their slender mouthparts into sieve elements, the primary food conduits of plants. Presence of the intracellular symbiotic bacteria that synthesize essential amino acids, aphids are role model for biological studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. More than 5,000 aphid species are known which attack agricultural plants and inflict damage.An annual loss of hundreds of millions of dollars havs been estimated dur to aphid attack.

Microsatellite or Simple Sequemce Repeats (SSR)

SSR are highly valueable marker in multi-allelic, codominance, and genetic polymorphism analysis. They are randomly distributed throughout the genome and could be further characterize into two types:

1. EST-SSR

2. Genomic SSR

Since EST-SSR are present in the transcribed region of genome, they are valuable in study of phylogentic study among the related species. However, genomic SSR could be efficiently used for genetic diversity study of a species.