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  • Author or Editor: Adrien Fónagy x
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Our current knowledge regarding primary structure, synthesis, release, receptor-binding, structure-activity relationship and mode of action of insect neuropeptides has increased dramatically during the past decade. Thanks to the development of insect neuroendocrinology -in parallel to this- an even increasing need for modern, yet environmentally sound strategies of plant protection has arisen, becoming a driving force for insect physiologists to concentrate their efforts to combat pests more efficiently. The ultimate aim of these researchers is, however, not the total eradication of harmful insects, but rather, selective targeting by using species- or group-specific control strategies which can only be achieved by taking note of recent results in insect physiology, endocrinology, biochemistry and ecology. The rationale behind this approach is, that, since neuropeptides regulate key biological processes, these“special agents”or their synthetic analogues, mimetics, agonists or antagonists may be effective tools in combating insect pests in an environmentally more sound manner than with conventional pesticides. In this review, taking into account possible practical aspects, some representative insect neuropeptides/groups have been selected, which may be important due to their characteristic structure and/or physiological action, and could be used for the design of novel, safe and selective compounds to control pests.

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Plant sucking aphids cause both quantitative and qualitative yield losses in cereals; moreover aphid-transmitted viruses are responsible for other quantitative and qualitative damages, thus direct or indirect effects of aphid infection are in focus of interest. Bread-making quality of wheat flour is determined primarily by the protein content and composition, the gluten proteins (glutenins, gliadins) being the prime factors. Allelic composition of the gliadin- and glutenin loci as well as the absolute amount and/or the relative ratio of gliadins to glutenins are very important in dough making and in determining baking quality. Wheat plants were caged at the beginning of stem elongation. Cages were treated with 0.1% methyl parathion. One week later, the caged plants were artificially infected with 5 alata individuals of Metopolophium dirhodum, Diuraphis noxia, Sitobion avenae and Rhopalosiphum padi. Flour from grains originating from plants infected artificially with cereal aphids were analyzed for glutenin and gliadin and total protein content, using Size Exclusion HPLC. It was found that aphid infection had significant effect on the glutenin and gliadin content, the total protein content and the gliadin/glutenin ratio. Both the glutenin and gliadin content was significantly higher in the seeds harvested from aphid infected plants. However, the gliadin/glutenin ratio was significantly lower in wheat flour prepared from aphid infected plants than in those from uninfected control. The most significant decrease in gliadin/glutenin ratio was caused by M. dirhodum, D. noxia, S. avenae infection followed by R. padi at high-abundance and low-abundance, respectively. As the gliadin/glutenin ratio was significantly lower in flours made from aphid infected wheat seeds, it may be suggested that aphid feeding results in decreased bread making quality of wheat flour.

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The need for more environmentally sound strategies of plant protection has become a driving force in physiological entomology to combat insect pests more efficiently. Since neuropeptides regulate key biological processes, these “special agents” or their synthetic analogues, mimetics, agonists or antagonists may be useful tools. We examined brain-suboesophageal ganglia and corpora cardiaca-corpora allata complexes of the cabbage moth, Mamestra brassicae , in order to obtain clues about possible peptide candidates which may be appropriate for the biological control of this pest. With the aid of bioassays, reversed phase high performance liquid chromatography, and mass spectrometry, five neuropeptides were unequivocally identified and the presence of a further three were inferred solely by comparing mass spectra with known peptides. Only one neuropeptide with adipokinetic capability was identified in M. brassicae . Data from the established homologous bioassay indicated that the cabbage moths rely on a lipid-based metabolism which is aided by an adipokinetic hormone (viz. Manse-AKH) that had previously been isolated in many different lepidopterans. Other groups of neuropeptides identified in this study are: FLRFamides, corazonin, allatostatin and pheromonotropic peptide.

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In Bombyx mori, pheromone-producing cells accumulate a number of lipid droplets in the cytoplasm preceding the production of the sex pheromone, bombykol. The process of lipid droplet formation in the pheromone-producing cells was investigated by using light and electron microscopy. Light microscopy revealed that the lipid droplets appeared from 2 days before adult eclosion and dramatic accumulation took place between 2 days and 1 day before eclosion. Electron microscopical studies revealed that smooth endoplasmic reticulum and numerous vesicles, their sizes being less than 1 µm, were detectable 2 days before eclosion, and some vesicles were fused with mitochondria at this stage. These characteristic changes in the pheromone-producing cells suggest that fatty acyl-CoA synthesis following de novo fatty acid synthesis takes place at this time. Involutions in the basal plasma membrane of the cells occurred throughout the observed period, which were extensive on the day before adult eclosion. Besides extensive basal involutions, immature lipid droplets appeared and then mature fully electron-dense lipid droplets were observed on the day of adult eclosion. These ultrastructural observations, combined with recent physiological studies suggest, that the basal involutions presumably reflect the uptake of lipidic components required for the construction of lipid droplets, the function of which is to store the bombykol precursor and to provide it for bombykol biosynthesis in response to pheromonotropic stimuli by pheromone biosynthesis activating neuropeptide (PBAN).

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