The effect of larval photoperiod on pupal colour and diapause in swallowtail butterflies

ABSTRACT. There are significant differences in the effects of larval photo‐period on diapause and pupal colour among the species Papilio polyxenes Fabr., P.troilus L., Battus philenor (L.) and Eurytides marcellus (Cramer). Diapause and pupal colour in P.polyxenes and P.troilus are strongly influenced by larval photoperiod, short photophase eliciting brown diapausing pupae. Photoperiods of 15L:9D permit the expression of the green and brown pupal colour alternatives. Pupal colour in B.philenor and E.marcellus is not affected by larval photoperiod, but short photophase induces diapause in these species. All species except B.philenor show an association between brown pupal colour and diapause: Emarcellus when reared on long (midsummer) photophase, P.polyxenes and P.troilus when reared on short (autumnal) photophase. In P.polyxenes , short photophase can affect pupal colour responses directly, whether the individual enters diapause or not. Differences among the species are related to differences in the ecology of their natural pupation sites.