ther species. The maximal similarity was observed with A. Scutellarein ipsilon, which was the closest phylogenetic relative with 95% and 98% similarity for positivity and identity, respectively. Bootstrap values were high in all nodes, and the topology was consistent with the current known phylogenies based on other genes. Regarding the insect species, Lepidoptera and Diptera clustered in phylogenetically coherent groups. Discussion In the present study, HaHMGR was cloned and characterized as the HMGR homologue from the cotton bollworm, H. armigera. This is the first report that used RNA interference to demonstrate the regulatory role of the HaHMGR gene on the oviposition of H. armigera. The results clearly suggested that silencing of the HaHMGR 27216982 gene influenced the fecundity of the females and effectively reduced the oviposition in H. armigera. Silencing the HaHMGR gene also decreased the levels of vitellogenin mRNA 
expression. RNAi of the HMGR Gene in the Helicoverpa armigera The HaHMGR gene showed the characteristic genetic organization of HMGR enzymes, which was confirmed by the following criteria: the cDNA yielded an amino acid sequence showing 98%, 90% and 88% homology with A. ipsilon, B. mori and S. cynthia ricini sequences, respectively; the hydrophobicity plot of the protein showed classical organization of animal-type HMGR with a N-terminal region containing the potential membrane-spanning domains followed by a short linker that connects the C-terminal region containing the catalytic domain; eight membrane-spanning domains were present in the hydrophobicity plot, which was consistent with other animal-type HMGR sequences; and the catalytic domain in the C-terminal region included His809, which is known to be a conserved region in all HMGR sequences characterized to date. Importantly, the relative levels of HaHMGR mRNA exhibited a significant increase in 4-day-old female pupae. Based on this result, 2-day-old female pupae were treated by injecting dsRNA 21836025 of the target gene to determine the efficiency of RNAi in moths at this developmental stage. Because RNAi is a knockdown method, silencing is not complete, and the effect is transient. The life stage of insects is one of the important factors that influences the silencing effect. We conducted experiments to choose the appropriate life stage in this moth for silencing the target gene. For example, no silencing effect was observed in the adult moth after treating 5th instar larvae of H. armigera with HaHMGR dsRNA by injection or feeding in the larval diets . A previous report has also shown that feeding long dsRNA to H. armigera larvae is not successful. In contrast, a strong silencing effect was observed in female moths after injecting dsRNA into 2day-old female pupae. The present results suggested that HaHMGR RNAi treatment effectively inhibited oviposition in H. armigera compared to the control. HMGR was the first gene to be cloned in the mevalonate pathway, and it is also the most widely studied gene in this pathway in insects because of its potential regulatory role in the production of JH in insects. It is likely that the knockdown of HaHMGR decreases the biosynthesis of JH and then reduces the expression of vitellogenins. In response to the suppression of JH, the mevalonate pathway can also produce other final products, such as dolichol, which behaves as a donor of oligosaccharide residues in the glycosylation of proteins, e.g., in the synthesis of vitellogenins in most insect species. I