Effects of ultralow doses of fenoxycarb on juvenile hormone–regulated physiological parameters in the silkworm, Bombyx mori L.

✍ Scribed by Hervé Monconduit; Bernard Mauchamp

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 194 KB
• Volume: 37
• Category: Article
• ISSN: 0739-4462
• DOI: 10.1002/(sici)1520-6327(1998)37:2<178::aid-arch6>3.0.co;2-q

✦ Synopsis

Effects of fenoxycarb at ultralow doses were investigated on juvenile hormone (JH)-regulated parameters in the silkworm, B. mori. Like JH, this non-terpenoid carbamate is able to induce permanent larvae in the last larval instar. However, whereas micrograms of JH are needed to produce this effect, only a few picograms of fenoxycarb are necessary to induce the same effect. The effects of fenoxycarb observed in this study were only visible from day 4 of the last larval instar-that is, when the JH titer has dropped to undetectable levels and JHrepressed physiological parameters would naturally be expressed. We observed that the permanent larvae induced with low doses of fenoxycarb (100 pg/larva) had no 20-hydroxyecdysone (20E) peak. Their prothoracic glands (PGs) were completely inactive and very weakly sensitive to prothoracicotropic hormone (PTTH). Fenoxycarb at doses of 1 ng/larva also significantly inhibited silk gland growth and coloration, whereas carotenoid content of the hemolymph was maintained at high levels, which could reflect an inhibition of its uptake by the silk glands. Total hemolymph protein levels in last instar larvae were also depressed at these doses. So, it seems that low doses of fenoxycarb are sufficient to maintain in a juvenilized status the physiological parameters that are normally expressed when JH titer has declined. Moreover, from an endocrinological viewpoint, we demonstrated that the corpora allata (CA) are not necessary for fenoxycarb to induce those effects and discussed its possible mode of action. Arch.