PHOTORECEPTION 181 



insect to specific wavelengths may vary with the physiological state. 

 Use (1928) has observed, for example, that cabbage butterflies {Pieris 

 brassicae) normally land preferentially on blue or yellow flowers or 

 paper models of the same colours, while gravid females ready to 

 oviposit shift their preference to green and blue-green (1937). On the 

 other hand, electrophysiological studies have confirmed the more 

 general behavioural findings (Crescitelli and Jahn, 1939; Jahn and 

 CrescitelU, 1939; Jahn, 1946; Jahn and Wulff, 1948; Donner and 

 Kriszat, 1950; Autrum and Stumpf, 1953; Goldsmith, 1958 a, 1958 b; 

 Goldsmith and Ruck, 1958; Walther, 1958 a, 1958 b; Walther and 

 Dodt, 1957, 1959). Spectral sensitivity curves were obtained in these 

 cases by relating the magnitude of some selected components of the 

 ERG to the wavelength of light or, more accurately, by plotting some 

 function of the quanta necessary to produce a given response against 

 wavelength. For the moth Samia cecropia (Crescitelli and Jahn, 1939) 

 and the grasshopper Melanoplus differentialis (Jahn and Crescitelli, 

 1939) the greatest sensitivity, exclusive of ultra-violet, which was not 

 tested, is in the blue-green (from about 460-530 mfi). The curve for 

 night and day eyes of Dytiscus fasciventris also shows a maximum 

 in the blue-green (about 520-575 m\L). It is based upon the magnitude 

 of the a wave. This was plotted against intensity. From the family of 

 curves (one for each colour) obtained, a constant response magnitude 

 was selected and plotted against wavelength (Jahn and Wulff, 1948). 

 Curves for Musca domestica, Lucilia caesar, Calliphora vomitoria, 

 Pollenia rudis, and Drosophila meJanogaster based upon measurements 

 of the on-efTect of the ERG at wavelengths of equivalent quantum 

 intensity show maxima in the green and in the near ultra-violet 

 (Donner and Kriszat, 1950). 



A spectral effectiveness curve for Calliphora erythrocephala shows 

 a peak at 540 m(x (blue-green) and one at 630 m\i (red) (Autrum and 

 Stumpf, 1953) (Fig. 89). This curve is based on the amplitude of the on- 

 effect of the ERG, or the height of the flicker potential occurring as a 

 reaction to twenty-seven flashes, produced by stimulation by light of 

 different wavelengths but equal quantal value. No tests were made 

 with ultra-violet, but the rising curve at the shorter wavelength 

 suggested ultra-violet sensitivity. This expectation was realized in tests 

 subsequently conducted by Walther (1957) and Walther and Dodt 

 (1957, 1959). A spectral sensitivity curve (reciprocal of the quanta 

 necessary to generate a constant magnitude of on-effect plotted as a 

 percentage of the maximum of 507 m(a against the wavelength) for 

 Calliphora shows maxima in the red (about 630 mjx), the blue-green 



