Rearing immatures of Euschistus tristigmus tristigmus in a range of photoperiods showed that a threshold photoperiod is involved in the adult dimorphic response (shoulder shape and number of midventral abdominal spots) with the mean threshold probably near 14.5L:9.5D (light: dark). This threshold is consistent with the seasonal distribution of the adult morphs.
McPherson, J. E.
"Effects of Various Photoperiods on Morphology in Euschistus Tristigmus Tristigmus (Hemiptera: Pentatomidae),"
The Great Lakes Entomologist, vol 12
Available at: https://scholar.valpo.edu/tgle/vol12/iss1/4