Cyanobacteria (“blue-green algae”) from marine and freshwater habitats are known to produce a diverse array of toxic or otherwise bioactive metabolites. However, the functional role of the vast majority of these compounds, particularly in terms of the physiology and ecology of the cyanobacteria that produce them, remains largely unknown. A limited number of studies have suggested that some of the compounds may have ecological roles as allelochemicals, specifically including compounds that may inhibit competing sympatric macrophytes, algae and microbes. These allelochemicals may also play a role in defense against potential predators and grazers, particularly aquatic invertebrates and their larvae. This review will discuss the existing evidence for the allelochemical roles of cyanobacterial toxins, as well as the potential for development and application of these compounds as algaecides, herbicides and insecticides, and specifically present relevant results from investigations into toxins of cyanobacteria from the Florida Everglades and associated waterways.

The synthesis of juvenile hormone (JH) is an attractive target for control of insect pests and vectors of disease, but the minute size of the corpora allata (CA), the glands that synthesize JH, has made it difficult to identify important biosynthetic enzymes by classical biochemical approaches. Here, we report identification and characterization of an insect farnesol dehydrogenase ( Aa SDR-1) that oxidizes farnesol into farnesal, a precursor of JH, in the CA. Aa SDR-1 was isolated as an EST in a library of the corpora allata-corpora cardiaca of the mosquito Aedes aegypti . The 245-amino acid protein presents the typical short-chain dehydrogenase (SDR) Rossmann-fold motif for nucleotide binding. This feature, together with other conserved sequence motifs, place Aa SDR-1 into the “classical” NADP ⁺ -dependent cP2 SDR subfamily. The gene is part of a group of highly conserved paralogs that cluster together in the mosquito genome; similar clusters of orthologs were found in other insect species. Aa SDR-1 acts as a homodimer and efficiently oxidizes C ₁₀ to C ₁₅ isoprenoid and aliphatic alcohols, showing the highest affinity for the conversion of farnesol into farnesal. Farnesol dehydrogenase activity was not detected in the CA of newly emerged mosquitoes but significant activity was detected 24 h later. Real time PCR experiments revealed that Aa SDR-1 mRNA levels were very low in the inactive CA of the newly emerged female, but increased >30-fold 24 h later during the peak of JH synthesis. These results suggest that oxidation of farnesol might be a rate-limiting step in JH III synthesis in adult mosquitoes.

Our understanding of JH biosynthesis has significantly changed in the last years. In this review I would like to discuss the following topics: (1) the progresses in understanding the JH biosynthesis pathway. Access to genome sequences has facilitated the identification of all the genes encoding biosynthetic enzymes and the completion of comprehensive transcriptional studies, as well as the expression and characterization of recombinant enzymes. Now the existence of different flux directionalites, feed-back loops and pathway branching points in the JH biosynthesis pathways can be explored; (2) the new concepts in the modulation of JH synthesis by allatoregulators. The list of putative JH modulators is increasing. I will discuss their possible role during the different physiological states of the CA; (3) the new theoretical and physiological frameworks for JH synthesis analysis. I will discuss the bases of the flux model for JH biosynthesis. JH plays multiple roles in the control of ovary development in female mosquitoes; therefore, the CA presents different physiological states, where JH synthesis is altered by gating the flux at distinctive points in the pathway; (4) in the final section I will identify new challenges and future directions on JH synthesis research.