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Abstract:

We are not far from celebrating the centennial of the introduction of the concept of locust density-dependent phase polymorphism (Uvarov, 1921) which causes the same locust species to occur in either a solitarious or gregarious phase. All current findings concerning this topic have been summarized recently (Pener and Simpson, 2009). Although both phases and some aspects of gregarisation are well described, the underlying molecular events of this phenotypic plasticity remain to be unravelled.During the past twenty years, the synthesis of several macromolecules (mRNA transcripts, peptides, proteins) have been shown to be differentially regulated or expressed in both phases. Although these molecules are clearly linked to the polyphenic phenotypes none of them acquired the status of being the primary inducer that triggers the phase-transition cascade. Neither can they explain how these two phases (phenotypes) are generated from one genotype, nor how the gregarious trait is passed on from generation to generation, nor how solitarious locusts can acquire gregarious characteristics during life. The center for regulation of behavioural gregarisation is likely to reside in the central nervous system (CNS). The first indications for grounding the latter were recently provided and indicated that the neurotransmitter serotonin was both necessary and sufficient to induce aggregating behaviour by topical application of serotonin solution on the metathoracic ganglion (Anstey et al., 2009). Nevertheless, more research is needed in order to elucidate both upstream and downstream players of the phase-transition cascade in order to target specific compounds towards the development of an unambiguous plague control strategy.Upon realizing that for drug delivery in the body, lipidization is a technique used in the pharmaceutical industry, we took into consideration that corazonin melanizes the cuticle of albino Locusta migratoria only when injected in an emulsion in oil and not when applied in an aqueous solution. In Boerjan et al., (2011a) we have shown that oral administration of corazonin in oil was not only active, it also induced red cuticular colouration in some animals, and it was also unexpectedly lethal for nymphs, but not for adults. These results necessitate the revision of the potential of (some) peptides for insect control. Also, they suggest practical recommendations for the application of other peptides in physiological assays where oil could be used as a simple slow release formula.The 21st century is in the biological field also called the post-genomic era. With the completion of full genomes of different organisms new analytical and bioinformatical approaches have emerged. One of the aims of this work was to explore whether the recently established locust EST-databases (Kang et al., 2004; Badisco et al., 2011a) might be used in combination with post-genomic approaches.We used the desert locust EST-database in order to analyse 90 selected protein spots of the prothoracic gland proteome. Of the latter fifty could be identified with an EST-based identification strategy. This implicates that the lack of genomic sequence information for the desert locust does not necessarily have to be a bottleneck for further proteomic experiments. Making use of the reverse genetics approach in the form of RNA interference, we are among the first to show that the function for the fruitless transcription factor has been conserved in hemimetabolous insects (Boerjan et al., 2011b). Copulation and copulation success are clearly affected by knocking down fruitless mRNA in early nymphal males. Analysis of post-mating effects in females suggests that sperm or seminal fluids might be affected by the fru RNAi treatment of males. Finally, we propose the possible involvement of an epigenetic model, involving DNA methylation, for locust phenotypic plasticity. The rationale and parallels with both vertebrate and invertebrate phenotypic plasticity are depicted. We show that the epigenetic machinery and functional DNA methylation are present in the desert locust. Our DNA methyltransferase expression profiles provide the first step in supporting this novel conceptual framework. Furthermore, our data suggests that longevity gets imprinted during the early larval stages, but further research will tell whether locust phenotypic plasticity is a true case of imprinting mediated by DNA methylation.