| Summary: | 碩士 === 國立中興大學 === 昆蟲學系所 === 95 === Cultured filtrate of the entomopathogenic fungus, Nomuraea rileyi SH1, seems contain proteinaceous substances which are inhibitory to larval growth of Spodoptera litura. The cultured filtrate of 12-h-culture were purified with ammonium sulfate precipitation, gel filtration, and hydrophobic interaction chromatography. SDS-PADE profile showed that the final toxic fraction consisted of two protein bands, both with a molecular weight of ca. 30 kDa and an isoelectric point of 9.7. Injection of S. litura fifth-instar larvae with the purified proteins caused 95.56% mortality. However, 40% of the filtrate-injected fifth-instar larvae was able to recover from growth retardation and to pupate normally when injected with 10-6 M 20-hydroxyecdysone every 24 h, totaling 7 times. The rescue effect on larval death by injection of 20-hydroxyecdysone was a dose-dependent response. Although 20-hydroxyecdysone at 10-4 M could rescue the filtrate-injected larvae from intoxication, their body weight increased slowly and fifth-instar duration extended 1-2 days. Once the sixth-instar larvae molted from the fluid-injected fifth-instars, they grew normally without any adverse effect and could emerge to adult. Injection of fifth-instar larvae with 20-hydroxyecdysone which had been treated with N. rileyi cultured filtrate (M20E) could not rescue the filtrate-injected larvae, resulting in only 7.5% pupation of these larvae. However, M20E-treated larvae which had been injected with fungal cultured filtrate could be rescued by injecting 10-4 M 20-hydroxyecdysone, resulting in 47.75% pupation. Therefore, it seems that the toxic proteins produced by N. rileyi SH1 interfere with hormonal action in S. litura.
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