Comparative Study On Effects Of Epibrassinolide And 20-hydroxyecdysone On Biological And Biochemical Characteristics Of Diamondback Moth

Brassinosteroids (BRs) are a class of plant polyhydroxysteroids, and the structures of BRs are similar to those of insect ecdysteroids. There are many common chacters in the physiological function of BRs and insect ecdysteroids. BRs play an essential role in the growth and development of plant, and have been recognized as a new kind of phytohormones. Now, BRs are used to improve the agronomic traits and ability to confront different stress of crops to increase yield and quality. The effect of BRs on insect is not well known now. 20-hydroxyecdysone (20E) is the main active one among insect ecdysteroids, and coorperated with juvenile hormone to mediate the decelopment and reproduction of insect.In order to explore the relathionship between BRs and 20E, effect of epibrassinolide and 20E on feeding of lava, development and reproduction of the diamondback moth (DBM), Plutella xylostella (L.), activity of protective enzyme and detoxifying enzymes, content of protein and titers of ecdysteroids in the insect body were comparied. The result showed that:Ingesting epibrassinolide and 20-hydroxyecdysone both exerted adverse effect on development and reproduction maily by causing encumbrance to metabolism, disturbing synthesis of protein and titers of ecdysteroids. There were difference between the characteristics of action of epibrassinolide and 20-hydroxyecdysone. When ingesting same concentration of 20E and epiBL, the adverse effects of 20-hydroxyecdysone to biology of diamondback was much stronger, and the adverse effect caused by ingesting epibrassinolide was much lasting not only in the same-concentration-treatment but also the same-stress-treatment.The different effects of epibrassinolide and 20E to DBM including (1) The development of larvae and pupae of DBM were delayed by ingesting brassinolide, while ingesting low concentrations of 20-hydroxyecdysone led to anticipation of molting of each instar larvae.(2) Epibrassinolide could not exert adverse effect on the feeding of 3rd instar of DBM larvae, while same concentrations of 20-hydroxyecdysone impeded the feeding of larvae by decreasing the food consumption during 24h and the whole instar. (3) Epibrassinolide did not exert repellent effect on oviposition of female adult of DBM, whle 20-hydroxyecdysone exerted significant repellent effect. (4) Epibrassinolide exerted adverse effect on embryonic development in eggs by decreasing the percentage of hatch and increasing the percentage of unembyonated eggs, while same concentrations of 20-hydroxyecdysone did not exert obvious adverse effect on embryonic development in eggs. (5) Epibrassinolide exerted more obvious induction effect to the activity of superoxide dismutase (SOD) and catalase (CAT) than 20-hydroxyecdysone, but could not inhibit the activity of peroxidease (POD); 20-hydroxyecdysone could obviously suppress the activity of POD; (6) The inhabitation effect of epibrassinolde was weaker than that of 20-hydroxyecdysone and the latter could significangtly inhibit the activity of carboxylesterase (CarE) and glutathione-s-transferase after treated for 24h and 48h.The common effects of epibrassinolide and 20E to DBM include (1) Ingesting epibrassinolide and 20-hydroxyecdysone both exert adverse effect on development of DBM larvae including making the duration of instar prolonged, weight gain during unit interval decreased and mortality of larvae increased; (2) Ingesting epibrassinolide and 20-hydroxyecdysone both led to decreasing of percentage of pupation, weight of pupae and percentage of emergence; and these phenomena were more obvious in experiments with high instar larvae tested; (3) Ingesting epibrassinolide and 20-hydroxyecdysone by the last instar larvae exert adverse effect on survival and reproduction of adult of diamondback moth, including led to the longevity of male adult obviously shortened, the fecundity of female adult decreased; (4) Ingesting epibrassinolide and 20-hydroxyecdysone both exerted adverse effect on synthesis of protein of protein of DBM larvae by decreasing the content of protein in body of the 4th instar of DBM after treated for 48h and 72 h. (5) Ingesting epiBL and20-hydroxyecdysone both exerted effect on the titer of ecdyseoids in that, at 24h after treatment, concentrations lower than 21.25 mg/kg of epibrassinolide led to slightly increase of titer of ecdysteroids in body of 4th instar larvae of DBM; at 48 h and 72 h after treatment, ingesting epibrassinolide could obviousy suppress the producing of ecdysteroids.