The mode of action of juvenile hormone (JH) is one of entomology’s longest standing mysteries. In the pine engraver beetle, Ips pini, pheromone components are produced de novo via the mevalonate pathway. Feeding and JH III treatment induce an increase in pheromone biosynthetic gene expression in male midgut cells, especially 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-R) and synthase (HMG-S). Microarray analysis has identified several mevalonate pathway genes, as well as a few unknowns, that appear to be JH-responsive. Further expression analyses using real-time and semi-quantitative RT-PCR prepared from midguts at various time points (within the first 8 hours) after JH treatment have revealed some that are rapid, primary JH-responders, with transcripts visible after only 1 hour. Curiously, HMG-R may be a secondary responder. The promoter regions of JH-responsive genes are needed to search for putative JH response elements. Therefore, an I. pini genomic library is being screened with JH-responsive clones in order to isolate their 5’ flanking regions. Important regions for induction will be mapped by transcriptional assays of GFP reporter constructs transfected into isolated midguts. The isolation of JH-inducible genes and their regulatory sequences will provide important information about the mechanism of JH action in the Coleoptera.
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