Spectral sensitivity and intensity thresholds in Nasonia photoperiodic clock

Abstract

FEMALES of the parasitic wasp Nasonia vitripennis give rise to diapausing progeny (fourth instar larvae) when maintained at short daylength (< 15.25 h/24) but to continuously-developing or non-diapause progeny at long daylength (>15.25 h/24) (ref. 1). Although the precise anatomical location of this photoperiodic ‘clock’ has not been determined, it is entirely maternal since the eggs are committed for either diapause or non-diapause development before they are deposited within the host blowfly puparium: by analogy with the aphid Megoura viciae² and the silkmoth Antheraea pernyi³, the clock and photoreceptors are probably in the brain. Photoperiodic time measurement in N. vitripennis is known to be a function of the circadian system⁴, and in all probability two separate circadian oscillators, one phase-set by the ‘on’ transition of the photoperiod and one by the ‘off’ transition, serve to ‘measure’ the phase-angle between ‘dawn’ and ‘dusk’⁵. Since, in principle, an experimentally observed action spectrum should correspond directly with the absorption spectrum of the pigment molecule involved and thereby lead to its identification, the spectral sensitivities of the ‘dawn’ and ‘dusk’ transitions of the daily photoperiod were determined for N. vitripennis.