Ultramicrochemistry of insect semiochemicals

Chemical ecology of the Insecta comprises an invisible environment where semiochemicals are the principal factors regulating the mating and host-selection of the one million or more species. Biologically effective concentrations of these semiochemicals range from 10^–10 to 10^–3 g at the insect antennal receptors. These levels are virtually undetectable by conventional microchemistry, and can be measured only by behavioral bioassay and by electrophysiology which are about 10,000 and 100-fold more sensitive than gas chromatography.Despite more than 40 years of study, the sex pheromones have been identified from only about 1300 species of insects (0.1%). The dearth of information about kairomones from host plants for phytophagous insects is even more astonishing, and only about 400 plant species have been studied extensively (ca. 0.2%), and the odorant spectra characterized in only 10 important crop plants. These odorants are chemically complex and their action as semiochemicals for insect herbivores, involves degrees of receptor specificity and synergism that are virtually unstudied.These lacunae in our knowledge of chemical ecology are fundamental to the study of ecology, behavior, and evolution of insects; but also are of vital importance in applied entomology. There is much societal pressure to progress from broadcast application of insecticides, to specific and innovative methods for insect control that are non-hazardous to human health and to environmental quality. Pest management strategies involving the use of semiochemicals are essential to reach this goal. These include monitoring insect populations vis-a-vis the economic threshold, the use of attracticide baits, and strategies for mating confusion and behavioral confusion of insect pest populations in row and orchard crops.The immensity of the semiochemical environments of plant and insect communities, the intellectual challenges for understanding ecology and evolution, and the immediate need for application to applied entomology provide compelling reasons for enhanced study of the microchemistry of semiochemicals.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

Analysis of cyanobacterial toxins by physicochemical and biochemical methods

Cyanobacteria (blue-green algae) produce a wide range of low molecular weight metabolites that include potent neurotoxins, hepatotoxins, and cytotoxins. The accumulation of such toxins in freshwaters, and in brackish and marine waters presents hazards to human and animal health by a range of exposure routes. A review is presented of developments in the detection and analysis of cyanobacterial toxins, other than bioassays, including application of physicochemical, immunoassays, and enzyme-based methods. Analytical requirements are considered with reference to recently derived guideline levels for the protection of health and to the availability, or otherwise, of purified, quantitative cyanobacterial toxin standards.