The rationale of "green pesticides" in food security is to use information about endogenous hormones of pest insects to make peptide mimetics that will act against the pest insects to alter their behaviour or physiology, while taking care not to harm beneficial insects or other organisms in the food chain. Such "green" insecticides are designed thus, on the basis of neuropeptide ligand-receptor interaction and it is of paramount interest to have finally a mimetic at hand that is harmful only to pest insects. For this concept to work, one has to identify the ligands in pest and beneficial insects. In this study we investigate adipokinetic hormones (AKHs) from a hemipteran source. The most harmful hemipterans on an economic scale are aphids (Hemiptera: Sternorrhyncha: Aphidoidea) of which the AKH is known. Here we identify the AKH complement of a member of a related suborder, the raintree bug or froghopper Ptyelus flavescens (Hemiptera: Cicadomorpha: Cercopoidea). Identification and sequence elucidation of the adipokinetic peptides of this species was achieved by a heterospecific and conspecific trehalose-mobilizing bioassay, and by liquid chromatography coupled to positive electrospray mass spectrometry (LC-ESI-MS) including tandem MS2spectra obtained by collision-induced dissociation. High resolution MS was employed to distinguish between Gln and Lys residues in the peptides. Three AKHs are discovered in the raintree bug: an octapeptide (Peram-CAH-I: pEVNFSPNW amide) previously known from cockroaches, and two novel decapeptides (Ptyfl-AKH-I: pEINFSTGWGQ amide and Ptyfl-AKH-II: pEINFSTAWGQ amide). The novel peptides were synthesized and the sequence assignments were unequivocally confirmed by co-elution of synthetic peptides and the natural equivalent and by identical MS data of the two forms. A conspecific bioassay in the froghopper describe the endogenous peptide Ptyfl-AKH-I as hypertrehalosemic. In heterologous bioassays the two novel AKHs induce an increase of circulating carbohydrates in cockroaches: Ptyfl-AKH-I is much more active than Ptyfl-AKH-II. Moreover, if the Ile2in Ptyfl-AKH-II is replaced with a Leu2residue, biological activity is further diminished. The current data show that the raintree AKH decapeptides differ by four amino acids from the aphid AKH (Acypi-AKH: pEVNFTPTWGQ amide). Therefore, it may be permissible to use the aphid AKH ligand-receptor pair to develop a "green" insecticide to target aphid metabolism.

Biology Centre Czech Academy of Sciences 37005 České Budějovice Czech Republic

Department of Biological Sciences University of Cape Town Private Bag Rondebosch 7700 South Africa

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