Identifying bird cherry‐oat aphid Rhopalosiphum padi emigrants, alate exules and gynoparae: application of multivariate methods to morphometric and anatomical features

Abstract

Multivariate analysis methods were used to distinguish between the three female alate morphs of Rhopalosiphum padi (L.) (emigrants, alate exules and gynoparae). Fourteen morphometric descriptors and seven anatomical parameters indicative of their potential fecundity were considered. Three populations or clones from distinct areas were also taken into account. The three alate morphs were separated with between 93% and 100% success. Some simplified criteria allowing distinction are described, and as an example one of them was applied to R. padi alatae caught in three suction traps. The reliability of the samples analysed is discussed. Practical use of identification techniques described may have implications for forecasting (e.g. Barley Yellow Dwarf Virus Disease), and for improving knowledge of aphid population biology. Résumé Recherche de critères morphométriques et anatomiques de différenciation des trois formes femelles ailées (émigrants, exules ailés et gynopares) du puceron des céréales Rhopalosiphum padi Des techniques d'analyse multivariée ont été appliquées sur des données morphométriques et anatomiques obtenues pour les trois formes femelles ailées (émigrants, exules ailés et gynopares) de Rhopalosiphum padi (L.) dans le but de les différencier. Pour cela des paramètres de la fécondité potentielle (nombre d'ovarioles, nombre d'embryons) et des variables morphologiques (mensurations, nombre de rhinaries) ont été évalués pour chacun des morphes sur des individus de trois populations ou clones d'origines géographiques distinctes (Angleterre, Normandie, Bretagne). Les analyses factorielles discriminantes réalisées sur ces données nous ont permis de séparer avec un taux de succès compris entre 93% et 100% les individus selon leur morphe. A partir de celles‐ci nous avons pu proposer des critères susceptibles de différencier ces trois formes ailées. Le rapport ARS/TARS2 (longueur de l'article apical du rostre/longueur du deuxième segment du tarse postérieur) semble très bien discriminer les émigrants des exules ailés et a été appliqué sur des ailés de R. padi capturés par deux pièges à succion français et un suisse. La séparation des gynopares des exules ailés est par contre moins simple. La représentativité de l'échantillon analysé a été discutée. Les possibilités d'application des méthodes d'identification des morphes de R. padi sur les ailés capturés aux pièges à succion ont été envisagées dans le cadre de la prévision des risques d'infection des céréales par le virus de la Jaunisse Nanisante de l'Orge (BYDV) et de l'amélioration des connaissances en Biologie des Populations aphidiennes.

Genetic diversity and mode of reproduction in French populations of the aphid Rhopalosiphum padi L.

“…These results suggest that in regions with cold winters, summer populations are largely recruited from holocyclic clones, whereas in areas with milder winters, summer populations are mainly derived from anholocyclic clones. Intermediate situations, where summer populations are an admixture of types, were found in the north of France, confirming the results of earlier morphological studies (Simon et a!., 1991b Our results suggest that allozyme analyses can be employed to infer the dominant mode of reproduction employed by populations of R. padi. Although the incidence of sexual reproduction might be esti-…”

Annotated expressed sequence tags for studies of the regulation of reproductive modes in aphids

“…It was maintained in conditions of continuous parthenogenetic reproduction under long photoperiod (16-h light/8-h dark) and warm temperature (18 v C). In order to enrich the cDNA library in transcripts upregulated under sexual-reproductive mode, insects were placed in sex-induction conditions using a standard protocol (Simon et al, 1991) (Fig. 1).…”

Geographic distribution and seasonal variation of mitochondrial DNA haplotypes in the aphidRhopalosiphum padi(Hemiptera: Aphididae)

“…Precise collection sites are available from the corresponding author. Individuals collected on the secondary hosts in early spring and late autumn were assumed to belong to obligately parthenogenetic populations first because their holocyclic counterparts typically shift back to P. padus by the end of the summer and do not return to the secondary hosts until the middle of May (Dixon & Glen, 1971;Simon et al, 1991b), and because their mode of reproduction was previously inferred from allozyme data (Simon et al, 1996a;Simon, unpublished data). Collections on the primary host in spring included only fundatrices (the first generation after sexual reproduction), while in autumn both gynoparae and males were collected.…”

“…However, there is no information on the frequency of such gene flow between cyclically and obligately parthenogenetic lineages in nature. Because direct breeding system determinations are extremely difficult and time consuming, several attempts have been made to differentiate between cyclic and obligate parthenogens of R. padi using morphological (Simon et al, 1991b;Lowles, 1995) or allozyme (Simon et al, 1996a) criteria. Recently, molecular markers linked to life-cycle variation have been identified in this aphid.…”