Adult nutrient shortage impairs female reproduction via the attenuated juvenile hormone signaling during vitellogenesis in <i>Helicoverpa armigera</i> (Lepidoptera: Noctuidae)

In insect reproduction, vitellogenesis is a prerequisite to oocyte maturation and critically depends on nutrient acquisition, supporting reproductive success. In Helicoverpa armigera (Hübner 1809), a hallmark of female reproduction is that vitellogenin (Vg) synthesis is initiated following adult eclosion, and juvenile hormone (JH) plays a principal role in this process. The adults commonly visit flowers to feed on nectar, which implies the possible linkage between adult nutrient and vitellogenesis. The preliminary experiment demonstrated that the supplemental nutrition with 10% honey during vitellogenesis significantly shortened the preoviposition period, extended the oviposition duration, and improved female fecundity. Ovary dissection showed that the ovarian development was somewhat delayed in water-fed females, while their ovarian degradation occurred in advance. Consistent with this, on days 1 and 2 of vitellogenesis, the water-fed females possessed a larger proportion of previtellogenic follicles in the ovaries and higher triglyceride content than those in honey-fed individuals. On days 3 and 4, the Vg transcription was significantly downregulated in the fat body of water-fed females. Besides, the water feeding during vitellogenesis resulted in an attenuated JH biosynthesis and a notable decline in intrinsic JH content. The expressions of JH pathway genes, Met and Kr-h1, in the fat body were reinforced in honey-fed females at day 4 of vitellogenesis. These results elucidated the promoting effect of adult nutrient on female reproduction, and we proposed that the adult nutrient shortage impairs female vitellogenesis partly via the attenuated JH signaling.