Innervation of the corpus allatum in the Colorado potato beetle as revealed by retrograde diffusion with horseradish peroxidase.

The application of horseradish peroxidase for tracing the cells innervating the corpus allatum in adult Leptinotarsa decemlineata, using simple instruments, is described. The corpus allatum in this insect appears to be innervated by a single group of about eight cells. The size and position of these cells indicate that they belong to the L-type lateral neurosecretory cells. The axons from each of these cells split into two pathways: one pathway arborizes extensively in the dorsal part of the brain adjacent to the pars intercerebralis whereas the other passes unbranched through the neuropil of the protocerebral lobe and corpus cardiacum into the corpus allatum. Additional cell groups in the pars intercerebralis which were stained when the corpus cardiacum was also contaminated with horseradish peroxidase are illustrated. The possible involvement of the lateral neurosecretory cells in the regulation of juvenile hormone biosynthesis is discussed.