Dormancy and the influence of photoperiod and temperature on sexual maturity in Nicrophorus nepalensis (Coleoptera: Silphidae)

Carrion beetles (Nicrophorus spp.) use small vertebrate carcasses for food and reproduction. Their ecology and behaviors are highly affected by the availability of carcasses and the surrounding environmental conditions. Our results revealed that in subtropical Fushan, northern Taiwan, N. nepalensis was mainly active in spring (February to May), and could also be found in autumn (October and November); but there was no capture record in summer (June to September) and winter (December and January). A laboratory temperature tolerance study indicated that N. nepalensis adults become inactive at temperatures above 26 degrees C, and had the highest mortality when the temperature was raised from 27 degrees C to 28 degrees C. Furthermore, N. nepalensis became sexually mature at 20 degrees C, depending on the photoperiod: the longer the day, the lower the percentage of sexually mature 2-week-old females after emergence. In another experiment, N. nepalensis virgins were paired under three possible conditions at Fushan. At 15 degrees C and 20 degrees C, if carcasses were presented to the pairs within 3 days after emergence, all laid eggs in the second week after emergence. If carcasses were presented 1 week after emergence, most began to reproduce at 20 degrees C with 12.5 h of daylight. However, at 15 degrees C with 11 h of daylight, the carrion beetles hibernated first, and reproduced in the ninth week after emergence. At 25 degrees C with 14 h of daylight, carrion beetles did not bury the mouse carcasses, the females did not lay eggs, and the adult lifespan was only one-third of that at 20 degrees C. This study revealed that both photoperiod and temperature influence the time needed to reach the sexual maturity of N. nepalensis; and also implied that the narrow temperature tolerance range and dormancy behavior of carrion beetles are highly regulated by those environmental factors.