In vivo and in vitro-tissue specific metabolism of juvenile hormone during the last stadium of the cabbage looper, Trichoplusia ni

Abstract

In vitro metabolism of racemic JH III (5 μM) was measured in fat body, midgut and integument homogenate during the last stadium of the cabbage looper, Trichoplusia ni. The JH esterase activity per mg protein peaked in these tissues in prewandering larvae on day 2 and was elevated in the fat body only in prepupae (on day 4). The JH epoxide hydrolase activity peaked on day 2 in midgut and on day 3 (in wandering larvae) in fat body and integument. No differences were noted in the overall JH III metabolism in vitro per insect between wandering (day 3) larvae and prepupae (day 4) and in the in vivo metabolism of 10R11S-JH II when injected in oil and buffer or when topically applied at physiological concentrations into these same stages. Regardless of the method of introduction of JH II, JH diol was produced in both wandering larvae and prepupae. JH acid and JH acid, diol were also produced but the predominant product was a water soluble metabolite. The preferred substrate for JH epoxide hydrolase at physiological concentrations was JH II as opposed to JH II acid. Approximately half of the JH II after injection into wandering larvae was associated with the alimentary canal and carcass. The metabolites of JH II were evenly distributed. The importance of JH epoxide hydrolase in JH metabolism in last stadium Lepidoptera is discussed.