A putative juvenile hormone in a stink bug,Plautia stali: The corpus allatum produces and releases a JH-active product different from any known JHs in vitro

Summary

A radiochemical method was adopted to analyze the in vitro products of the corpus allatum (CA) of Plautia stali. The radiolabel derived from ³H-methionine added to the incubation medium was incorporated and released by CA as two main radiolabelled products. They showed Rf values of about 0.3 and 0.5, respectively, in the thin layer chromatography (TLC) system used. The release of these products was shown to be CA-specific since in control incubations using the brain, midgut, aorta and flight muscle, virtually no release of these products was observed. The locations where these main products migrated on the TLC did not coincide with spots of synthetic standards of JH I-III or JHB₃, a JH found in higher Diptera. An addition of precursors of JH III, farnesoic acid or farnesol stimulated the CA to biosynthesize the products with an Rf value of 0.5 up to about 10-fold, suggesting that the product in question may have a sesquiterpenoid skeleton similar to JH III. Topical applications of the hexane extracts of the medium in which the CA had been incubated exerted a juvenilizing, metamorphosis-inhibiting effect on final instar nymphs in a dose-dependent fashion. The nymphs treated with the hexane extracts at a high dose moulted to intermediates with reduced forewings and scutellum, as well as nymphs implanted with the CA from reproductively active females. Based on this juvenilizing effect found in the hexane extracts, the JH-active fraction was determined after TLC separation. This assay indicated that the products found at an Rf value of about 0.5 was JH-active. These results suggest the presence of a new JH different from any known JHs in P. stali.     

Effects of low temperature on diapause termination and body colour change in adults of a stink bug, Plautia stali

Abstract. Diapause adults of Plautia stali Scott maintained at 20°C under short day conditions (LD 12:12 h) were exposed to four temperatures of 5–20°C to examine the effect on diapause development which was assessed in terms of oviposition. Diapause adults kept at 20°C under short day conditions changed their body colour gradually from brown to green and started egg laying after a prolonged preoviposition period. Those transferred to either 10 or 15°C also showed colour change but did not lay eggs. Bugs exposed to 5°C underwent neither body colour change nor oviposition and died more rapidly than those kept at higher temperatures. When 30-day-old diapause adults were chilled at 5, 10 or 15°C for 30 or 60 days and returned to 20°C and long day conditions (LD 16:8 h), the preoviposition period varied primarily depending on the chilling, but not on the temperature. On the other hand, when 60day-old diapause adults chilled for 30 days were observed at 20°C and long day conditions, their preoviposition period tended to be longer as the chilling temperature was lower In this case, a temperature of 10°C appeared to intensify diapause. Therefore, the effect of chilling on diapause development varied depending on the age at which insects were chilled. When chilled bugs were transferred to short day conditions at 20°C, most females failed to lay any eggs and some turned green, then after a while, some green bugs changed to brown again. These results indicate that bugs remained sensitive to short day conditions even after a 60-day chilling at 10 or 15°C.