Abstract
The life-cycles of three species of Rhopalosiphum commonly occurring in Hokkaido were surveyed, especially on their primary host. Though they have different species of winter host trees, i. e. Prunus (Pad us) for padi (L.), Sorb us, Malus and Crataegus for insertum (Walker), and Prunus (Prunophora) and Malus for rufiabdominale (Sasaki), seasonal occurrence of the morphs was similar in three species. Grown fundatrices were seen in May. Emigrants and apterous fundatrigeniae were observed in June, though in rufiabdorninale continued to occur even in July. The apterous fundatrigeniae of insertum were rarely found as said in Europe. Gynoparae may emerge in later half of September, and were observed on trees in October. Males and oviparae were also seen in October.
