Night-interruption experiments and action spectra for dawn and dusk in relation to the photoperiodic clock of the cabbage whitefly,Aleyrodes proletella (Homoptera: Aleyrodidae)

The dark period (scotophase) is the most photoperiodically important part of a light-dark cycle in Aleyrodes proletella. Night-interruption studies have revealed three distinct dark stages: the photosensitive stage 1 lasts for about 3 h after dusk and 1-h light breaks both stop and re-set the photoperiodic clock; stage 2 also lasts about 3 h, but is photorefractory to some degree; stage 3 is photosensitive, but short light breaks do not re-set the clock although a 4-h light break (equivalent to a main photophase) does restore the capacity to respond to a normal critical night length in the post-interruption scotophase.Action spectra revealed peak photoperiodic sensitivity to blue light (410–430 nm) with 50% responses., at 1.5 μWcm⁻² and 2.5 μWcm⁻² for the dusk and dawn peaks respectively. These data are consistent with the view that the photopigment is a carotenoprotein.The results are interpreted in terms of the photoperiodic clock in A. proletella operating on the hour glass principle.