Variation in the photoperiodic response within natural populations ofMyzus persicae(Sulz.)

Abstract

In laboratory experiments, the responses to short photoperiod (10 h) of clones ofMyzus persicae(Sulz.) established from random samples of summer populations in southern England were generally stable and characteristic for each clone, and were of four distinct categories: (i) holocyclic, with clones terminated under short photoperiod by production of male and female sexual forms, (ii) intermediate, with a mixed response involving alatae intermediate between gynoparae and virginoparae, (iii) androcyclic, with production of some males along with continued parthenogenesis, and (iv) truly anholocyclic, with no significant response to short photoperiod. All four types can occur within one population, but holocyclic and androcyclic forms are most common. There were clear differences in the proportions of these forms occurring simultaneously on adjacent crops of different host-plants, and in different years on the same crop in the same field. Males of androcyclic clones were able to transmit their partially anholocyclic character through the sexual phase.