Bimodal life cycle of the burying beetle Nicrophorus quadripunctatus in relation to its summer reproductive diapause

Abstract

1. Under natural conditions in Kyoto, Japan, the reproductive activities of Nicrophorus quadripunctatus Kraatz (Coleoptera: Silphidae) decreased in summer and the species showed a bimodal life cycle. 2. In the laboratory, most adult pairs raised at 20°C under a LD 12:12 h regime reproduced when provided with a piece of chicken. In adults raised at 20°C under a LD 16:8 h regime, however, both reproductive behaviour and ovarian development were reduced. It is concluded that these adults entered a reproductive summer diapause. 3. High temperature (25°C) also suppressed the reproductive behaviour even under a favourable LD 12:12 h regime. In the field, therefore, adults reduce their reproductive activity in summer because of diapause induced by long-day photoperiods and direct inhibition of reproduction by high temperatures. 4. When the temperature was changed from 20°C to 25°C immediately after hatching of larvae, they reached the wandering stage in 95% of adult pairs. When the temperature was changed from 20°C to 25°C immediately after oviposition, however, no larvae hatched in 85% of pairs. Egg mortality was significantly higher at 25°C than at 20 and 22.5°C; no eggs hatched at 27.5°C. The physiological mechanisms for reducing reproduction probably prevent the beetles from inefficient oviposition in summer.