Maladaptive photoperiodic response in an invasive alien insect, Milionia basalis pryeri (Lepidoptera: Geometridae), in southern Kyushu, Japan

Abstract

The geometrid moth, Milionia basalis pryeri Druce, is an important pest of Podocarpaceae trees that has recently become established in the southern part of the main island of Kyushu, Japan. The species exhibits a multivoltine seasonal life cycle, with adults emerging mostly from spring to autumn, and occasionally being observed in winter. In this study, life-history traits and overwintering success were examined for a population collected in southern Kyushu. A long-day photoperiodic response was shown in larval and pupal development, with larvae and pupae developing significantly more slowly under short-day conditions than under long-day conditions. The critical photophases for this response were 12–13 h/day at 20 °C and 10–12 h/day at 25 °C. In the field, only individuals that pupated at a particular time in autumn remained in the pupal stage during winter, but all of them failed to eclose normally to adults, although some of them attained the wing pigmentation stage in winter to spring. This maladaptive seasonality in M. basalis pryeri in southern Kyushu is attributed to inconsistency between the climate of the new habitat and the innate ability of M. basalis pryeri to respond to seasonal cues, and is considered to be an ecological cost of a range-expanding insect.