The ‘interval timer’ and photoperiod in the determination of parthenogenetic and sexual morphs in the aphid, Drepanosiphum platanoides

Abstract

The ability of the sycamore aphid to produce sexuales (males and females) is regulated by a timing mechanism (‘interval timer’) which restrains the appearance of these morphs in the spring under short day conditions. In this species there are two ‘interval timers’: one, sensitive to day-length and controlling the production of sexual females, and another insensitive to day-length and controlling the production of males. In the production of sexual females day-length acts directly on the aphid and not through the host plant. The restraining effect of the ‘interval timer’ results in a gradual transition from parthenogenetic to gamic reproduction over a period of several generations and is still operational in the autumn. This enables the sycamore aphid to continue very effectively to exploit its host plant at a time when it provides a rich food source, although some individuals ensure continuity of the population by laying eggs before any premature adverse conditions.