Fenoxycarb, a potent contaminant of the silkworm, Bombyx mori L., does notinfluence its juvenile hormone titer

Fenoxycarb (FC) effects were studied on juvenile hormone (JH) titers and JH -esterase activities in the silkworm, B. mori. In the literature, FC was ob served to induce high JH titers but also to act without corpora allata (CA) . These contradictory results did not permit us to conclude whether FC was a potent JH mimic or it was acting through the enhancement of JH titers in the hemolymph. Analysis of hemolymph JH-esterase activities during the last larval instar reveals that FC was not a JH-esterase inhibitor. Considering JHs, only JH II was detected in the European hybrid 200x300. Furthermore, JH titer was exactly identical in control and FC-treated larvae, i.e., it d ropped during the first 2 days of the last larval instar and became undetec table after day 2. This result is important since it contradicts the genera lly admitted concept that FC was acting by increasing the titer of JH. On t he contrary, it was found that, despite its non-terpenoid chemical structur e, FC might be a JH mimic. In addition, FC suspected contamination of mulberry leaves was analyzed fro m a physiological viewpoint, me observed that "contaminated" mulberry leave s-fed larvae became permanent larvae through the inhibition of their protho racic glands (PC;) activity and without any modification of their JH titers , i.e., exactly as for FC-treated larvae. This last point adds information concerning the suspected implication of FC in the induction of the non-spin ning syndrome. (C) 1999 Wiley-Liss, Inc.