Queried GO terms:

  idGO:0009648   Detailed information
  namephotoperiodism
  namespacebiological_process
  def"Any process that results in a change in state or activity of an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of detection of, or exposure to, a period of light or dark of a given length, measured relative to a particular duration known as the 'critical day length'. The critical day length varies between species." [GOC:jid, GOC:pj, ISBN:0582015952, ISBN:0697037754, ISBN:0709408862]
  synonym"response to day length" EXACT []
  synonym"response to night length" EXACT []
  synonym"response to photoperiod" EXACT []
  xrefWikipedia:Photoperiodism
  is_aGO:0009416 ! response to light stimulus

Monarch genes with this GO terms:

  DPGLEAN08466