Abstract
The Chinese citrus fruit fly, Bactrocera minax, is an economically important pest of citrus. It exhibits pupal diapause from November to May to combat harsh environmental conditions. Such a long pupal diapause is a barrier for laboratory rearing and development of control strategies against this pest. In the present study, 20-hydroxyecdysone (20E) was used to break pupal diapause of B. minax by topical application. After diapause termination by 20E treated, the pupal ontogenetic processes were observed along the temporal trajectory. The pupal response time to 20E was estimated by detecting the relative expression of 20E responsive genes at different times after 20E-treatment. Results revealed that 20E could effectively terminate the pupal diapause in a dose-dependent manner and significantly shorten the time for 50% adult emergence (Et50). 20E response genes, including ecr, broad and foxo, were up-regulated within 72h, indicating these genes are involved in pupal metamorphosis and diapause termination processes. Morphological changes showed the pupal metamorphosis began ~7 days after 20E-treatment at 22 °C. This study does not only pave the way for artificial rearing in the laboratory through manipulating of pupal diapause termination, but also deepens our understanding of the underlying pupal diapause termination mechanism of B. minax.
Highlights
A salient feature of insect’s life cycle is diapause, which is a genetically determined response to environmental stimuli, such as dehydration, extremely low or high temperatures, scarcities of food and other hostile conditions[1]
B. minax pupal diapause could be effectively terminated by topical application of 20E in a dose-dependent manner (Fig. 1)
The results from this study indicate that topical application of 20E on the B. minax pupae plays a crucial role in pupal diapause development and termination
Summary
A salient feature of insect’s life cycle is diapause, which is a genetically determined response to environmental stimuli, such as dehydration, extremely low or high temperatures, scarcities of food and other hostile conditions[1]. Pupal diapause can be terminated by different ways, including environmental cues, chemicals and hormonal stimuli. Bactrocera minax (Enderlein) (Diptera: Tephritidae) is an important economic pest of citrus in China and its neighboring countries[20,21] It is univoltine with long pupal diapause, which is a great obstacle for artificial rearing and development of control strategies against this pest. The relative mRNA expression of these genes, including ecr, foxo, broad, bhr[3], e74a and vrille[33,34], were detected with quantitative real-time polymerase chain reaction (qRT-PCR) after pupae topically treated with 20E to further understand the mechanism of pupal diapause in B. minax
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