Morphometric and molecular discrimination of the sugarcane aphid, Melanaphis sacchari, (Zehntner, 1897) and the sorghum aphid Melanaphis sorghi (Theobald, 1904).

Samuel Nibouche,Roger L. Blackman,Jocelyn R. Holt,Anne-Sophie Zoogones,Joëlle Sadeyen,Laurent Costet,Paul Brown,Raul F. Medina,Bernd Schierwater

doi:10.1371/journal.pone.0241881

Abstract

Melanaphis sacchari (Zehntner, 1897) and Melanaphis sorghi (Theobald, 1904) 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.

Highlights

The species Melanaphis sacchari [1] and Melanaphis sorghi [2] were described at the turn of the 20th century by Zehntner [1] on sugarcane in Java and by Theobald [2] on sorghum in Sudan respectively
Using Blackman & Eastop’s (2006) key, we identified these specimens as M. sacchari or M. sorghi, but the identification sometimes was ambiguous given the continuous and overlapping nature of the criteria used to separate both species
We examined the Theobald type series of Aphis sacchari collected in Sudan in 1902, which is stored in the Natural History Museum of London (NHM)

Summary

Introduction

The species Melanaphis sacchari [1] and Melanaphis sorghi [2] were described at the turn of the 20th century by Zehntner [1] on sugarcane in Java and by Theobald [2] on sorghum in Sudan respectively. The objectives of this study were (1) to improve the description of the morphometric differences between M. sorghi and M. sacchari, and (2) to delimit the molecular separation of M. sorghi and M. sacchari

Material and methods

Findings

Methods