Microsatellite Markers Reveal a Predominant Sugarcane Aphid (Homoptera: Aphididae) Clone is Found on Sorghum in Seven States and One Territory of the USA

The sugarcane aphid (Melanaphis sacchari) has become a serious pest causing severe economic losses to sorghum [Sorghum bicolor (L.) Moench] grown in the southern United States. Since its original detection in four states in 2013, M. sacchari on sorghum has now, in 2016, spread to 19 states. The presence of one or multiple genotypes on sorghum in the United States has not yet been established. In this study, genome sequencing of M. sacchari was used to develop microsatellite markers. A total of 8,665,267 reads and 1.44 Gb of nucleotide sequences were generated, and 79.6% of the reads were from M. sacchari. Melanaphis sacchari DNA from 46 samples from 17 locations across seven states and one US territory was polymerase chain reaction (PCR) amplified using 38 newly created microsatellite markers, as well as 14 published microsatellite markers. Genotyping with the 52 microsatellite markers indicated that the samples of M. sacchari on sorghum were all one genotype, with the exception of a single sample collected from Sinton, TX, which had the predominant genotype as well as another genotype. Genotyping of the aphid samples with 12 microsatellite markers for Buchnera aphidicola, the obligate aphid symbiont, had nearly identical results. The invasive M. sacchari on sorghum appears to be spreading in the United States on sorghum as primarily one asexual clone.