Mitochondrial COI and morphological evidence for host specificity of the black cherry aphids Myzus cerasi (Fabricius, 1775) collected from different cherry tree species in Europe (Hemiptera, Aphididae)

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

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.

Geographical variation in morphology of Chaetosiphella stipae stipae Hille Ris Lambers, 1947 (Hemiptera: Aphididae: Chaitophorinae)

Chaetosiphella stipae stipae is a xerothermophilous aphid, associated with Palaearctic temperate steppe zones or dry mountain valleys, where there are grasses from the genus Stipa. Its geographical distribution shows several populations that are spread from Spain, across Europe and Asia Minor, to Mongolia and China. Geographical variation in chaetotaxy and other morphological features were the basis to consider whether individuals from different populations are still the same species. Moreover, using Ch. stipae stipae and Stipa species occurrences, as well as climatic variables, we predict potential geographical distributions of the aphid and its steppe habitat. Additionally, for Stipa species we projected current climatic conditions under four climate change scenarios for 2050 and 2070. While highly variable, our results of morphometric analysis demonstrates that all Ch. stipae stipae populations are one very variable subspecies. And in view of predicted climate change, we expect reduction of Stipa grasslands. The disappearance of these ecosystems could result in stronger separation of the East-European and Asian steppes as well as European 'warm-stage' refuges. Therefore, the geographic morphological variability that we see today in the aphid subspecies Ch. stipae stipae may in the future lead to speciation and creation of separate subspecies or species.

Congruence between cytochrome oxidase I (COI) and morphological data in Anuraphis spp. (Hemiptera, Aphididae) with a comparison between the utility of the 5' barcode and 3' COI regions

The discrimination of species in the genus Anuraphis is particularly difficult due to the overlap of morphological characters. In this study, we used the 5' (barcode) and 3' regions of cytochrome oxidase I (COI) to test their utility in the identification of species in this genus as well as closely related species. Both regions were useful to discriminate all the species tested. However the non-barcode 3' region resulted in higher resolution and support for species relationships when the data were analyzed using both Maximum Likelihood and MrBayes. We propose the development of an integrated database that encompasses morphological, molecular, life-cycle, host plant and bibliographic information to facilitate and increase the accuracy of aphid identification.