Morphometric and Molecular Discrimination of Melanaphis sacchari (Zehntner, 1897) and Melanaphis sorghi (Theobald, 1904)

Nibouche S, Costet L, Medina RF, Holt JR, Sadeyen J, Zoogones AS, Moretti S, Halbert SE, Blackman RL

PLoS One 2020, DOI:x

This is code to replicate the analyses of the morphometric data reported in our manuscript. Code developed by Samuel Nibouche (samuel.nibouche 'at' cirad 'dot' fr) | 2020

Abstract

Melanaphis sacchari (Zehntner) and Melanaphis sorghi (Theobald) are major worldwide crop pests causing direct feeding damage on sorghum and transmitting viruses to sugarcane. It is common in the scientific literature to consider these two species as synonyms, referred to as the ‘sugarcane aphid’, although no formal study has validated this synonymy. In this study, based on the comparison of samples collected from their whole distribution area, we use both morphometric and molecular data to better characterize the discrimination between M. sacchari and M. sorghi. An unsupervised multivariate analysis of morphometric data clearly confirmed the separation of the two species. The best discriminating characters separating these species were length of the antenna processus terminalis relative to length of hind tibia, siphunculus or cauda. However, those criteria sometimes do not allow an unambiguous identification. Bayesian clustering based on microsatellite data delimited two clusters, which corresponded to the morphological species separation. The DNA sequencing of three nuclear and three mitochondrial regions revealed slight divergence between species. In particular, the COI barcode region proved to be uninformative for species separation because one haplotype is shared by both species. In contrast, one SNP located on the nuclear EF1-α gene was diagnostic for species separation. Based on morphological and molecular evidence, the invasive genotype damaging to sorghum in the US, Mexico and the Caribbean since 2013 is found to be M. sorghi.

Data analysis

Data

Morphometric data are available at DOI:10.18167/DVN1/PDPDS4

Code

Use 'SAS code apterous.md' for univariate analysis of apterous data with SAS.
Use 'SAS code alates.md' for univariate analysis of alate data with SAS.
Use 'R code.md' for multivariate analysis of apterous data with R.