IP Endocrinology

The first adipokinetic hormone isolated from a dermapteran insect

noptera: Megachilidae)

Department of Animal Ecology 1, University of Bayreuth, 95440 Bayreuth, Germany

The adipokinetic/red pigment-concentrating hormone family (AKH/RPCH) of neuropeptides represents one of the largest peptide families in arthropods. In insects, where more than 30 members of this peptide family are known from about 70 species, representing 11 of the 27 extant pterygote orders, they are mainly involved in the release of lipids, carbohydrates and amino acids from the fat body, inhibition of lipid, protein and RNA biosynthesis and in neuromodulation/myoregulation. Although the Deramaptera are one of the commonly known and relatively conspicous insect orders, no information on their AKH is available. Therefore, we choose the common earwig Forficula auricularia for the first study on dermapteran AKHs. Paired corpora cardiaca (pCC) were dissected (from animals that had been collected in the vicinity of Bayreuth), immediately transferred into ice-cold acidic methanol and extracted twice. The crude extract (equivalent to 214 pCC) was purified by high-performance liquid chromatography (HPLC) on a C18 reversed phase column using a gradient of acetonitrile in water, containing 0.1% trifluoro-acetic acid. Only one prominent peak with a retention time similar to synthetic Gryllus bimaculatus-AKH (Grb-AKH) showed strong adipokinetic activity when injected into earwigs at a concentration of 1 pCC equivalent. Equal amounts of the native Forficula-AKH and synthetic Grb-AKH were co-chromatographed on the HPLC using four solvent systems with different selectivities. In each run, the two peptides eluted as a single pure peak, confirming the identity of the Forficula-AKH with Grb-AKH (pQVNFSTGWamide), which had previously been found only in ensiferan species and recently in wasps. Upon injection of synthetic Grb-AKH, haemolymph (HL) lipid titres (control level: 17 mg lipids/ml HL as measured with the sulphophosphovanillin method) rose in a dose-dependent manner (threshold concentration of 0.05 pmol Grb-AKH, maximum increase 152% at 10 pmol injected). Haemolymph carbohydrates (control levels: ca. 4 mg total carbohydrates/ml HL as measured with the anthrone method; 65% trehalose, 35% glucose as determined by HPLC) did not change significantly at up to 10 pmol Grb-AKH injected, however, some increase of HL carbohydrates occurred due to the handling of the animals. Only at the highest dose injected (50 pmol) a significant increase in HL carbohydrates was observed. These results suggest, that F. auricularia, although not a flying insect, uses mainly lipids as a fuel.

Index terms: Forficula auricularia, Gryllus bimaculatus, AKH, lipid mobilisation

Copyright: The copyrights of this original work belong to the authors (see right-most box in title table). This abstract appeared in Session 18 – REPRODUCTION AND DEVELOPMENT Symposium and Poster Session, ABSTRACT BOOK II – XXI-International Congress of Entomology, Brazil, August 20-26, 2000

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Zoology - Analysis of Complex Systems 103 (2000), Supplement III, page 89 (Lorenz, M.W.: The adipokinetic hormone of the common earwig, Forficula auricularia (Dermaptera)). Note, that after these abstracts had been accepted, I became aware that a paper by Gaede, G. (Physiol. Entomol. 24, 327-332 (1999) had been published during the review process, descibing the isolation and characterization of an adipokinetic hormone from two earwigs (Labidura riparia and Forficula auricularia) that is identical to the adipokinetic hormone described in the above abstracts.