SPECTRAL EFFICIENCY OF THE WESTERN FLOWER THRIPS, FRANKLINIELLA-OCCIDENTALIS

Western flower thrips have sexually-dimorphic swarming behaviour in which many males (but not females) aggregate on flowers and artificial substrates of only certain colours. To test whether this behavioural dimorphism has a physiological basis involving gender differences in the peripheral visual system, we recorded the thrips' electroretinogram from 365 to 620 nm and determined spectral efficiency. The thrips' electroretinogram is a phasic-tonic cornea-negative potential with no OFF potential change. With both male and female thrips, our results demonstrated two peaks of spectral efficiency, one in the ultraviolet range and one in the visible with lambda(max) around 540 nm. Differences between the sexes were minimal with females having a greater efficiency than males in the ultraviolet. Thus the gender differences in attractiveness of certain colours for the western flower thrips is not solely due to differences in spectral properties of the photoreceptors, but results from higher order processing mediating the behavioural choices of males.