Time of the season: the effect of host photoperiodism on diapause induction in an insect herbivore, Leptinotarsa decemlineata

Diapause, seasonal physiological dormancy, is the primary life history strategy used by insect species inhabiting temperate climates for seasonal synchronisation. Biotic signals for diapause induction originating from host plants may provide dependable cues for insects expanding from subtropical regions. We investigated the effect of plant‐mediated photoperiod cues on diapause initiation within the Colorado potato beetle, Leptinotarsa decemlineata Say. The effect of photoperiod changes on potato leaf composition and its subsequent correlation with diapause initiation was tested. Analyses revealed a significant effect of short‐day ( LD 8 : 16 h and LD 10 : 14 h) photoperiod growth regimens on both nitrogen content in potato leaves and diapause initiation within L. decemlineata . Potato plants grown under short day conditions displayed significantly higher levels of leaf nitrogen compared with long‐day treated plants. Over 65% of beetles feeding upon short‐day treated plants initiated diapause compared with