Fenoxycarb levels and their effects on general and juvenile hormone esterase activity in the hemolymph of the silkworm, Bombyx mori

We studied the relationship between fenoxycarb levels and general esterase (GE) activity, juvenile hormone esterase (JHE) activity, and induction of permanent fifth instar (dauer) larvae in Bombyx mori. Fenoxycarb (1 mug/animal) was topically applied to B. mori at 0 h of the fifth instar. Hemolymph fenoxycarb levels, as determined by an ELISA, reached a peak within I h, and then decreased to undetectably low at 42 h. After 48 h, the feces of these larvae contained 99% of the applied fenoxycarb dose. The above fenoxycarb treatment induces dauer larvae with persistently increased hemolymph GE and JHE activities for the rest of the fifth instar. Application of fenoxycarb later in the fifth instar (48 h), when it still could induce dauer larvae, resulted in a similar pattern of elimination from the hemolymph and produced steadily elevated hemolymph GE and JHE activities for the rest of the fifth instar. Application of fenoxycarb late in the fifth instar (132h) did not prevent pupal ecdysis; it increased hemolymph JHE activity, but not GE activity. The latter treatment prevented the JHE activity decrease observed in control larvae before pupal ecdysis. In vivo, in control animals, the highest hemolymph JHE activity was observed 12 h after pupal ecdysis. At that developmental time, fenoxycarb inhibited this enzyme in vitro (IC50 approximate to 2 muM). The combined results suggest: (1) fenoxycarb, is rapidly excreted from the larval body; (2) induction of dauer larvae and increased hemolymph GE and JHE activities are not directly associated with its presence in the larval body of B. mori. (C) 2002 Elsevier Science (USA). All rights reserved.