The photoperiodic counter in the black bean aphid, Aphis fabae

Abstract

The photoperiodic counter mechanism in the black bean aphid, Aphis fabae, was analysed by exposing newly-born, presumptive gynoparae to a variety of photoperiodic regimes at 15°C, and by the development of a model. It was shown that the counter accumulated long as well as short scotophases and that the “inductive strength”, or “value”, of long and short scotophases depended on photophase duration. Whilst the value of a long, 12-h, scotophase increased when accopanied by long photophases (>32 h), the value of a short, 8-h, scotophase decreased when accompanied by short photophases (<14 h). There was no detectable change in sensitivity to either long or short nights during the 4-day postnatal sensitive period. The counter mechanism appeared similar to that of the vetch aphid Megoura viciae, except that in M. viciae the value of a 12-h scotophase decreased with long photophases, whilst it increased in A. fabae.