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The feeding cycle of the adult female cockroach Blattella germanica parallels vitellogenesis. The study of the mechanisms that regulate this cycle led us to look for food-intake inhibitors in brain extracts. The antifeedant activity of brain extracts was tested in vivo by injecting the extract and measuring the carotenoids contained in the gut from carrot ingested after the treatment. By HPLC fractionation and tracking the biological activity with the carrot test, we isolated the sulfakinin EQFDDY(SO 3 H) GHMRFamide (Pea-SK). A synthetic version of the peptide inhibited food intake when injected at doses of 1 mg (50% inhibition) and 10 mg (60% inhibition). The sulfate group was required for food-intake inhibition. These biological and structural features are similar to those of the gastrincholecystokinin (gastrin-CCK) family of vertebrate peptides. However, heterologous feeding assays (human CCK-8 tested on B. germanica, and Pea-SK tested on the goldfish Carassius auratus ) were negative. In spite of this, alignment and cluster analysis of these and other structurally similar peptide families suggest that sulfakinins and gastrin -CCKs are homologous, and that mechanisms of feeding regulation involving these regulatory peptides may have been conserved during evolution between insects and vertebrates.Keywords: Blattella germanica; food-intake control; German cockroach; sulfakinin.How do insects regulate food intake and satiety? The answer holds an obvious academic interest, but it may also offer great potential for the design of new insecticides. Indeed, the induction of immediate satiety may prevent the attack of insects on our crops and stored food.In vertebrates, a variety of mechanisms are involved in the regulation of food intake and energy balance, for example, physiological signals such as neuronal inputs related to circadian rhythms, metabolic signals reflecting the rate of use of various energy sources by brain and abdominal viscera, gastrointestinal signals elicited by gastric distension, and the release of peptides from the gastrointestinal tract in response to nutrient ingestion that act on the brain [1,2]. Most of these factors are peptides, which may be peripheral, central or circulatory. Satiety factors include: the short-term and peripheral peptides cholecystokinin (CCK), bombesin, enterostatin and glucagon-like peptide-1; the central peptides corticotropin-releasing factor and melanocortin; and the long-term circulatory proteinaceous factor leptin. Conversely, hunger factors are central and include neuropeptide Y, galanin and orexin [3].The equivalent information has not been acquired for insects, although recent developments indicate that the endocrine regulation of physiological processes is at least as complex as in vertebrates. Therefore, thorough research in this field may unveil the factors involved in the presumably complex regulatory systems governing food intake in insects.The adult females of anautogenous insect species, which require food as a prerequisite for oogenesis, are suitable ex...

Ecdysteroid hormones regulate key developmental processes throughout the life cycle of insects. 20-Hydroxyecdysone (20E) acts upon binding to a heterodimeric receptor formed by the nuclear receptors EcR and USP. The receptor, once 20E bounds to it, elicits cascades of gene expression that mediate and amplify the hormonal signal. The molecular characterization of the 20E-mediated hierarchy of transcription factors has been analyzed in detail in holometabolous insects, especially in Drosophila melanogaster, but rarely in more basal hemimetabolous species. Using the hemimetabolous species Blattella germanica (German cockroach) as model, we have cloned and characterized five isoforms of B. germanica E75, a member of the nuclear receptor family participating in the 20E-triggered genetic hierarchy. The five isoforms present characteristic expression patterns during embryo and nymphal development, and experiments in vitro with fat body tissue have shown that the five isoforms display specific 20E responsiveness. RNAi experiments in vivo during the penultimate and last nymphal instars of B. germanica revealed that BgE75 is required for successfully complete nymphal-nymphal and nymphal-adult transitions. Detailed analysis of knockdown specimens during the last nymphal instar showed that BgE75 is required for the rise of circulating ecdysteroids that occurs towards the end of the instar. The main cause of ecdysteroid deficiency in BgE75 knockdowns is the premature stage-specific degeneration of the prothoracic gland. As a consequence, BgE75 knockdown nymphs do not molt, live for up to 90 days and start the adult developmental program properly, in spite of remaining as nymphs from a morphological point of view. Finally, RNAi of specific isoforms during the last nymphal instar of B. germanica has showed that they are functionally redundant. Furthermore, it also revealed the occurrence of a complex regulatory relationship among BgE75 isoforms, which is responsible of their sequential expression.