Reproductive Strategies of the Alate Morphs of the Bird Cherry-Oat Aphid Rhopalosiphum padi L.

Host alternating aphids like the bird cherry-oat aphid exist in several distinct morphs (Dixon 1973). The alate morphs are difficult to separate morphologically (Rogerson 1948) but are easily separated behaviourally. The emigrants leave the primary host, bird cherry, Prunus padus L., before the end of June and colonize various grasses. The alate exules, which are then produced on the secondary hosts, spread to other grass plants. Triggered by fall in temperature and decrease in day-length in autumn, exules no longer produce more exules, but gynoparae and males instead, which finally return to the primary host on which the aphid overwinters as an egg (Dixon & Glen 1971). Each morph in the sequence that is produced in the annual cycle of a host alternating aphid has a different function to perform. Associated with their different functional roles it is acceptable that these morphs also exhibit different reproductive strategies. It is the aim of this paper to describe these differences in the reproductive behaviour of all the alate female morphs of Rhopalosiphum padi L. and to relate the differences to the aphid's way of life.