Diapause and cold tolerance inAsian species of the parasitoidLeptopilina(Hymenoptera:Figitidae)

Abstract

AbstractDiapause and cold tolerance are essential for temperate insects to pass the winter, with the mechanisms controlling these two traits varying considerably among insects. In the present study, diapause and cold tolerance are compared among threeLeptopilinaspecies:Leptopilina japonicaNovković & Kimura,Leptopilina victoriaeNordlander andLeptopilina ryukyuensisNovković & Kimura, all larval parasitoids of frugivorous drosophilid flies, with the aim of understanding their climatic adaptations. The first species is divided into the temperate (Leptopilina japonica japonica) and subtropical subspecies (Leptopilina japonica formosana), and the latter two species are distributed in the tropical and subtropical regions. The temperate subspecies ofL. japonicaenters prepupal diapause at low temperatures (15 or 18 °C), irrespective of photoperiod, and some individuals enter diapause when exposed to 0 °C for 1 or 2 day(s) or when placed at low humidity.Leptopilina victoriaealso shows signs of diapause initiation at 15 °C, althoughL.ryukyuensisandL. j. formosanafrom the subtropical regions do not. Preimaginal viability at low temperature (13, 14 or 15 °C) is usually lower inL. victoriaefrom the tropical regions compared withL. japonicaorL. ryukyuensisfrom the temperate or subtropical regions. Diapausing prepupae of the temperate subspecies appear to be cold tolerant. However, the cold tolerance of nondiapausing prepupae, pupae and adult females varies little among the tropical, subtropical and temperate species or subspecies, and adult males of the temperate subspecies ofL. japonicaare less cold tolerant than those of the tropical or subtropical species or subspecies. Cold tolerance may be unnecessary, except for diapausing individuals of the temperate species, because nondiapausing individuals appear in warmer seasons.