title: Effects of juvenile hormone (JH) analog insecticides on larval development and JH esterase activity in two spodopterans.
abstract: Juvenile hormone analog (JHA) insecticides are biological and structural mimics of JH, a key insect developmental hormone. Toxic and anti-developmental effects of the JHA insecticides methoprene, fenoxycarb, and pyriproxyfen were investigated on the larval and pupal stages of Spodoptera littoralis and Spodoptera frugiperda. Bioassays showed that fenoxycarb has the highest toxicity and fastest speed of kill in 2nd instar S. littoralis. All three JHAs affected the development of 6th instar (i.e., final instar) and pupal S. frugiperda. JH esterase (JHE) is a critical enzyme that helps to regulate JH levels during insect development. JHE activity in the last instar S. littoralis and S. frugiperda was 11 and 23 nmol min(-1) ml(-1) hemolymph, respectively. Methoprene and pyriproxyfen showed poor inhibition of JHE activity from these insects, whereas fenoxycarb showed stronger inhibition. The inhibitory activity of fenoxycarb, however, was more than 1000-fold lower than that of OTFP, a highly potent inhibitor of JHEs. Surprisingly, topical application of methoprene, fenoxycarb or pyriproxyfen on 6th instars of S. littoralis and S. frugiperda prevented the dramatic reduction in JHE activity that was found in control insects. Our findings suggest that JHAs may function as JH agonists that play a disruptive role or a hormonal replacement role in S. littoralis and S. frugiperda.
authors.affiliation: Department of Entomology and Nematology, and the UC Davis Cancer Center, University of California, Davis, CA 95616, USA; Department of Plant Protection, Faculty of Agriculture, University of Zagazig, Zagazig 44511, Egypt.
authors.forename: El-Sayed A
authors.initials: el-SA
authors.lastname: El-Sheikh
authors.affiliation: Department of Entomology and Nematology, and the UC Davis Cancer Center, University of California, Davis, CA 95616, USA.
authors.forename: Shizuo G
authors.initials: SG
authors.lastname: Kamita
authors.affiliation: Department of Entomology and Nematology, and the UC Davis Cancer Center, University of California, Davis, CA 95616, USA. Electronic address: bdhammock@ucdavis.edu.
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Hammock
mesh_terms: D000818:Animals; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism; D007306:Insecticides / Q000494:pharmacology*; D007605:Juvenile Hormones / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects* / Q000254:growth & development; D018411:Spodoptera / Q000254:growth & development*
chemical_list: D007306:Insecticides; D007605:Juvenile Hormones; D002265:Carboxylic Ester Hydrolases; C038003:juvenile hormone esterase
keywords: Inhibition; JH esterase; Juvenile hormone (JH) analog insecticide; S. frugiperda; Spodoptera littoralis