The role of temperature and photoperiod in diapause induction in the brassica leaf beetle, Phaedon brassicae (Coleoptera: Chrysomelidae)

Abstract

The brassica leaf beetle, Phaedon brassicae Baly (Coleoptera: Chrysomelidae), one of the pests infesting cruciferous vegetables in China and Japan, is a multivoltine species that oversummers and overwinters as an adult. The effects of both temperature and photoperiod on reproductive diapause induction were systematically investigated in this beetle. Under 16L : 8D, most of the beetles entered reproductive diapause at 12-30°C, indicating that photoperiod played a crucial role in estivation diapause induction. Under 12L : 12D, all adults developed without diapause at 28 and 30°C; less than 25% of the individuals entered reproductive diapause at 16-24°C; however, 46.1% of the individuals entered diapause at 12°C, suggesting that low temperature also had a relatively important influence on the determination of diapause. The photoperiodic response curves indicate that this species is a typical short-day species. The critical day-lengths at 20, 24 and 28°C were 13.2, 13.6 and 13.8 h, respectively. Transferring them from 16L : 8D to 12L : 12D or vice versa at different ages and/or stages during their development revealed that the photoperiod experienced by adults during the first 11 days might be important for diapause determination, even though an effect of photoperiod on the larval and pupal stages can not be excluded. Transferring individuals kept at a photoperiod of 12L : 12D from 25°C to 12°C or vice versa at different ages and/or stages during their development revealed that the temperature cue for diapause is mainly perceived by the late instar larvae and pupae.

Keywords

• chrysomelidae
• brassica leaf beetle
• phaedon brassicae
• photoperiod
• reproductive diapause induction
• temperature