Diapause hormone terminates larval diapause in the bamboo borer, Omphisa fuscidentalis (Hampson)

- Various concentrations of Ompfu-DH successfully terminate larval diapause in O. fuscidentalis.
- Ompfu-DH increases the hemolymph ecdysteroid level in diapausing larvae of O. fuscidentalis.
- The responses of larval diapause to Ompfu-DH may rely on the sensitivity of larvae.

The larvae of the bamboo borer (Omphisa fuscidentalis Hampson) maintain a diapause state for approximately nine months. However, changes in the ecdysteroid titer lead to the termination of larval diapause when juvenile hormone analogue (JHA) is applied. The hormonal mechanisms that terminate larval diapause are still unknown. Recently, it was found that the O. fuscidentalis diapause hormone and pheromone biosynthesis activating neuropeptide genes (Ompfu-DH-PBAN) were expressed during the development of both larvae and pupae and during the late larval diapause. This result suggested that diapause hormone (DH) might be involved in the termination of larval diapause. Thus, our study aims to determine the effect of DH on diapause termination in the bamboo borer. The response of diapausing larvae to DH was assayed using the synthesized O. fuscidentalis diapause hormone (Ompfu-DH). After injection with different concentrations of DH (25, 50 and 100 ng/larvae), nearly half of the individual larvae (approximately 45%) became completed or incompleted pupae within 30 days. The mean days of pupation in larvae injected with 25, 50 and 100 ng DH were 26.81 ± 17.86, 26.30 ± 16.45 and 25.30 ± 16.12, respectively. The hemolymph ecdysteroid titer in Ompfu-DH injected-larvae was significantly higher 10-15 days after Ompfu-DH injection and reached a maximum before the formation of the pupal cuticle. These results indicate that Ompfu-DH terminates larval diapause in O. fuscidentalis by increasing the ecdysone in hemolymph, reflecting a new role of DH in the regulation of larval diapause in this species.

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