Insecticidal activity and up-regulation of juvenile hormone response genes by juvenile hormone agonists in the western flower thrips, Frankliniella occidentalis

Insect juvenile hormone (JH) agonists have been utilized as insect growth regulators for pest management against several pest insect species. We investigated insecticidal activity and the induction ratios of two JH-inducible genes, Krüppel homolog 1 (Kr-h1) and broad (br), using 12 test compounds in the western flower thrips Frankliniella occidentalis (Pergande). In insecticidal assays against propupae to inhibit metamorphosis to the adult, the activities of pyriproxyfen, KF-13, ETB, and KF-31 were potent at 10 mM, while those of the other 8 test chemicals were not. In quantitative RT-PCR, these 4 chemicals up-regulated the transcript levels of Kr-h1 and br, while the induction of transcription by chemicals with lower insecticidal activities was relatively small. Thus, the induction ratios of Kr-h1 and br correlated with insecticidal activity. Assessments of the induction ratios of these genes may be a useful method in the preliminary screening of JH agonists.