Rearing immatures of Thyanta calceata in a Iange of photoperiods showed that a threshold photoperiod is involved in the adult dimorphic response (color and pubescence) with the mean threshold near 12.5L: 11.5D. This threshold is consistent with the seasonal distribution of the adult morphs.
McPherson, J. E.
"Effects of Various Photoperiods on Color and Pubescence in Thyanta Calceata (Hemiptera: Pentatomidae),"
The Great Lakes Entomologist, vol 11
Available at: https://scholar.valpo.edu/tgle/vol11/iss3/5