Identification And Expression Pattern Of JH-related Genes In Plutella Xylostella And Their Responses To External Modulators

The diamondback moth (DBM), Plutella xylostella (L.), is a destructive pest of cruciferous crops all over the world. It has high fecundity and can become resistant to any insecticide within a comparatively short time. It is in great necessities of new management measures. Juvenile hormone (JH) is the most important hormone of insects and has become a key target for new insecticide development. In this thesis, based on the genome data of DBM(www.iae.fafu.edu.cn/DBM), the candidate genes involved in synthesis, transportation, metabolism and reception were identified. The expression pattern of all the candidate genes in different life stages as well as in different tissues was investigated. The effect of starvation, short-term high temperature,3-octylthio-1,1,1-trifluoro-2-propanone (OTFP), pyriproxyfen and the combination of these two chemicals on survival, growth and development of the third instar larvae of DBM was studied. Meanwhile, the changes in the expression of above mentioned genes and juvenile hormone esterase (JHE) activity after treatments were detected.The gene Px009591 was identified as the candidate gene of juvenile hormone acid methyl-transferase (JHAMT), Px010755 as nuclear juvenile hormone binding protein (nuclear JHBP), Px010760 as hemolymph juvenile hormone binding protein(hJHBP), Px016154 as juvenile hormone esterase binding protein (JHEBP) and Px004734 as juvenile hormone receptor (methoprene-tolerant, Met). All the genes were expressed in egg, larva, pupa and adult stages of DBM. Compared in the four instars, they were all expressed highest in the 4th instar larvae. For different tissues, they were all expressed highest in fatbody.After 48h of starvation, the mortality of the tested insects increased and the molting rate decreased. Both the expression and its activity of JHE decreased. Also, the expression of both nuclear JHBP and hJHBP decreased, but that of JHAMT and Met genes increased.After 24h of treatment at 32 ℃, the molting rate of the tested insects increased. Both the JHE gene expression and its activity of JHE increased. Meanwhile, the expression of the genes of JHEBP, nuclear JHBP and hJHBP also increased but that of JHAMT and Met decreased.Treatment with OTFP delayed the molting time of the 3rd instar larvae. The pupation of the 4th instar larvae was postponed and the pupation rate decreased but the pupal weight increased. For gene expression, only that of JHEBP increased, but the others including JHAMT, nuclear JHBP, hJHBP, JHE and Met decreased.Pyriproxyfen treatment delayed the molting time of the 3rd instar larvae and inhibited the pupation of the 4th instar larvae completely. Both JHE gene expression and its activity increased. The expression of JHEBP and Met genes increased but that of JHAMT, nuclear JHBP and hJHBP decreased.After being treated with the combination of OTFP and pyriproxyfen, the mortality of the tested insects increased and the pupation was completely inhibited. The expression of JHE, JHEBP and Met genes increased and JHE activity increased, too. But the expression of JHAMT, nuclear JHBP and hJHBP decreased.