LIFE-CYCLE AND MORPH PRODUCTION IN THE ARCTIC APHID ACYRTHOSIPHON BREVICORNE

The life-cycle of the sub-Arctic, Dryas-feeding aphid, Acyrthosiphon b revicorne, is described and shown to be intermediate between that of t he high-Arctic aphid (Acyrthosiphon svalbardicum) and typical holocycl ic, monoecious, temperate species. The fundatrix of A. brevicorne can give rise directly to both sexual morphs, a necessary adaptation to th e short Arctic summer. Production of males is predetermined; some male s are produced by all-viviparous mothers, but at lower frequencies in the birth sequences of the fundatrix than in subsequent generations. B y contrast, the production of oviparae is controlled, at least in part , by photoperiod.