1978] 
Shapiro — Pierid Butterflies 
281 
expression and ultimately couple it to a reliable seasonal predictor, 
normally a pre-existing photoperiodic control of diapause. 
This postulated evolutionary sequence can be further rationalized 
by noting that the pattern of interaction among genetics, photo- 
period, and temperature is completely in accord with Darwinian 
predictions. For multivoltine species, which in Pieridae are weedy 
colonizers, photoperiodic determination of diapause can be over- 
ridden by high temperature in some individuals, allowing them to 
gamble on an extra generation in an unusually warm autumn. But 
photoperiodic determination of vernal phenotype is absolute; this 
makes sense insofar as autumn is colder than summer and any 
direct-developing butterflies will be aided in their feeding and repro- 
ductive activities by the thermoregulatory properties of the vernal 
phenotype. Estival phenotypes are not irreversibly determined by 
summer photoperiods. Cold can act on the young pupa just a few 
days before hatch to produce more or less of the vernal phenotype, 
giving rise to darker animals on short notice in unseasonably cold 
conditions. Hoffmann’s Rocky Mountain C. p. eriphyle and Sha- 
piro’s coastal P. n. venosa are commonly exposed to unseasonable 
cold and switch readily without regard to photoperiod. But lowland 
C. eurytheme and P. protodice, which rarely face such conditions, 
are arcane enough in their “sensitive period” characteristics that 
they were missed altogether in laboratory experiments for years. 
Acknowledgements 
I thank Sydney Bowden for bringing Lorkovic’s paper to my 
attention and for sending me a translation of the German summary, 
and Prof. Dr. Z. Lorkovic for lending me an original copy of the 
paper, for amplifying on its contents, and for, in his words, feeling 
“content to live so long to see that I was discovered after 49 years, 
indeed!” 
Literature Cited 
Barker, R. J., A. Mayer, and C. F. Cohen. 
1963. Photoperiod effects in Pieris rapae. Ann. Entomol. Soc. Amer. 56: 
292-294. 
Bowden, S. R. 
1978. Seasonal polyphenism in Artogeia napi (L.) (Lep.: Pieridae). Ent. Rec. 
90: 176-180. 
