The Expression Of Heliocoverpa Armigera SCP-2 In Different Tissues And The Bioassay Of The Of Biological Activity Of SCP-2 Inhibitors

Cholesterol is an important component of insect celluar membranes (total membrane composed of 14%) and as a precursor for the molting hormone (ecdysone) and the other hormones.It play an important role in physiological and metabolic processes of insects. Insects lack key enzymes in the cholesterol synthesis pathway, so they do not synthesize cholesterol de novo,and must obtain cholesterol in the diet. This physiological constraint implies that cholesterol absorption/transport is particularly important for insects.Therefore, the SCP-2 that involved in cholesterol uptake/translocation is a validated target for the development of novel larvicides. The mosquito SCP-2 is a validated target for the developing novel mosquitocide,and some mosquito sterol carrier inhibitors were screened,which are effective on lethality to mosquito.Some Aedes aegypti SCP-2 inhibitors also block cholesterol binding SCP-2 and lethal to Manduca sexta (Lepidoptera). SCP-2s in Lepidoptera are also potential targets for insecticide.In experiment, we do reserch in the unique target Lepidoptera Helicovera armigera SCP-2, the differential expression of HaSCP-2 in different tissues and different developmental periods, and the biological activity of its inhibitors.First, we used RT-PCR technique to detect the transcription of HaSCP-2 gene in different tissues of H. armigera larvae,and the HaSCP-2 transcription is detectable in feeding larvae with little tissue-specific profiles. To determine the quantitative differences of HaSCP-2 expression in different tissues including Fat body(FB), Malpighian tube(Mt), Hindgut(Hdg),Midgut(Mdg),Epidermis(Ep) and Head of different instars including the fourth instar (day1 and 2), the fifth instar (day1,2and 3), The levels of transcripts was determined via qPCR analysis. The highest levels of HaSCP-2 mRNA were detected in the midgut samples, whereas all other tissues had detectable levels of transcripts during the feeding stages.It showed the lepidopteran larval midgut is the site of sterol absorption, Therefore, the spatial transcription profiles of the HaSCP-2 gene is consistent with its proposed role in aiding cholesterol uptake in the midgut.To test the effect of the SCP-2 inhibitors on the growth and development of Helicoverpa armigera, We used SCPI inhibitors (SCPI-2 and SCPI-7)with a series of concentration gradient (0.1 mM, 1mM, 10mM,25mM) testing its biological activity in Helicoverpa armigeram, and the experiment was carried out from the first day of first instar Helicoverpa armigera larvae. The results showed that the SCPI-2 treated larvae experienced weight gain and it is more effective against young instars than to those in the final growth period; very small amount of them development process was slow; some become black before pupation and could not pupate; few of the pupa could not change to moths or in the prosess of changing to moth they were blocked, resulting in the pupa shell was exuviate incomplete. These results suggested that the SCPIs has a certain impact on the Helicoverpa armigera.This experiment laid the foundation to clarify the the molecular structure of the HaSCP-2 gene,and play an important role in reveling the role of this gene in cotton bollworm growth and development. It laid the foundation to identification of HaSCP-2 inhibitors,which is an important step toward the development of targeted new insect growth regulators.