Morph identification in natural populations of alate female bird cherry aphids, Rhopalosiphum padi L., by multivariate methods

A discriminant analysis was done to determine which morphological characteristics contributed most to the identification of alate female morphs of Rhopalosiphum padi in natural populations collected from either Prunus padus or in suction traps. Twenty two characters were measured or counted, including wing dimensions, and three ratios were included. Analyses were done to separate morphs that might occur naturally together, i.e. emigrants and 'early' exules, or 'late' exules and gynoparae. Emigrants were distinguished readily from early exules, but gynoparae were not so easily separated from late exules. The biological significance of the morphological: differences between morphs and the practical implications of being able to identify the different morphs are discussed.