Evidence for a Phe-Gly-Leu-amide-like allatostatin in the beetle Tenebrio molitor

The allatostatins (ASTs) with Phe-Gly-Leu-amide C-terminal sequence are multifunctional neuropeptides discovered as inhibitors of juvenile hormone (JH) synthesis by corpora allata (CA) of cockroaches. Although these ASTs inhibit JH synthesis only in cockroaches, crickets, termites and locusts, isolation of peptides or of cDNA/genomic DNA or analysis of genomes indicates their occurrence in many orders of insects with the exception of coleopterans. The gene for these ASTs has not been found in the genome of the red flour beetle Tribolium castaneum (Family Tenebrionidae). Yet, in view of widespread occurrence of these peptides in insects, crustaceans and nematodes, they would be expected to occur in beetles. This study provides evidence for the presence of FGLa-like ASTs in the tenebrionid beetle, Tenebrio molitor, and scarabid beetle, Popillia japonica. Extract of brain from both beetles inhibited JH synthesis by cockroach CA dose dependently and reversibly. 20 brain equivalents of T. molitor and P. japonica extracts inhibited JH synthesis 64 ± 5 and 65 ± 0.6% respectively. Antibody against cockroach allatostatin (Diploptera punctata AST-7) used in an enzyme-linked immunosorbent assay reacted with brain extract of these beetles. Antibody against D. punctata AST-5 localized FGLa-like ASTs in the brain and subesophageal ganglion of T. molitor and P. japonica. In addition, pretreatment of T. molitor brain extract with anti-D. punctata AST-5 reduced the inhibition of JH synthesis and pretreatment of anti-D. punctata AST-5 with D. punctata AST-5 diminished the immunoreactivity of the antibody. Thus we predict that FGLa-like allatostatins will be found in beetles.