Pheromone dispersal

This review considers evidence for selective forces that mold the chemical signal and behavioral response, including the characteristics of pheromone dispersal and the plume-tracking maneuvers that influence the success of mate finding. Recent reviews that consider mechanisms of evolutionary change in moth pheromones include Phelan (1992,1996,1997), Lofstedt (1993), Linn and Roelofs (1995), and Lofstedt and Kozlov (1996). 

Wright (1958) and Bossert and Wilson (1963) independently introduced the use of Sutton s equation to analyze pheromone dispersion in the wind. Bossert and Wilson solved the equation for the maximum distance of communication ... 

Fares et al. (1980) were the first to apply a general Gaussian plume model (3.5) to pheromone dispersion and the first to emphasize the importance of atmospheric stability on pheromone communication. They used dispersion coefficients derived from tracer experiments conducted in a pine forest. They hypothesized that the diurnal pattern of bark beetle responses to pheromone may relate to diurnal changes in stability. (For further discussion of the selective forces influencing diurnal activity patterns see Card6 and Baker, Chapter 12.)... 

Our research on pheromone dispersion has been supported by NSF Grant PMC 7912014 and by a grant from the USDA Expanded Gypsy Moth Program. We are greatly indebted to Conrad Mason, John Murlis, Roger Shaw and Ralph Charlton for invaluable discussion and review of this paper. 

These examples show that, in addition to the posited interspecific effects of competition for an exclusive communication channel, other factors including energetics, predation, pheromone dispersion, physiochemical constraints, and stabilizing selection, may dictate the design of these signals. We will now consider in detail the sexual communication system of the oriental fruit moth, G. molesta, as an example of the interplay of the chemical and non-chemical signals in sexual communication and the potential role of sexual selection. 

The other major class of extracellular LBPs of mammals is the lipocalins (Flower, 1996). These are approximately 20 kDa, P-sheet-rich proteins, performing functions such as the transport of retinol in plasma or milk, the capture of odorants in olfaction, invertebrate coloration, dispersal of pheromones, and solubilizing the lipids in tears (Flower, 1996). The retinol-binding protein (RBP) of human plasma is found in association with a larger protein, transthyretin, the complex being larger than the kidney threshold and thus not excreted, although the RBP itself may dissociate from the complex to interact with cell surface receptors in the delivery of retinol (Papiz et al., 1986 Sundaram et al., 1998). 

One recent study addressed the response of a parasitoid to the host s spacing pheromone. Aphidius rhopalosiphi did not respond to the spacing pheromone of one host, the cherry-oat aphid Rhopalosiphum padi, which consists of 6-methylhept-5-en-2-one 16,6-methylhept-5-en-2-ol, tridecan-2-one and methyl salicylate. These compounds did not attract or repel the parasitoid. Because the aphid spacing pheromone can potentially be used to cause aphids to disperse, the failure of the parasitoid to respond to the spacing pheromone makes simultaneous use of the spacing pheromone and the parasitoid possible in aphid management [87]. 

Although not studied extensively, males of social hymenoptera certainly produce pheromones. Male ants produce aggregation pheromones that attract both sexes to mating areas [6] as well as cause virgin alates to disperse from their colony [ 6 ]. However, these have not been chemically elucidated. 

One may wonder why lobsters appear to use urine as a dispersal solvent for chemical signals, whereas terrestrial arthropods such as the well-studied insects use direct release of gland products into the air. Perhaps the answer is that small animals in air (such as insects) are always in danger of desiccation. By contrast, marine lobsters and crabs are relatively large and may experience only minor water loss problems due to osmosis. Thus, it may not be difficult for a 500-g lobster to store 10 ml of urine and release it during a dominance battle at a rate of up to 1 ml/min (27). The advantage of urine-carried pheromones is that the dispersal mechanism already exists urine is injected into the gill current, which in turn injects into ocean currents. 

Pheromone propagation by wind depends on the release rate of the pheromone (or any other odor) and air movements (turbulent dispersion). In wind, the turbulent diffusivity overwhelms the diffusion properties of a volatile compound or mixture itself. Diffusion properties are now properties of wind structure and boundary surfaces, and preferably termed dispersion coefficients. Two models have dominated the discussion of insect pheromone propagation. These are the time-average model (Sutton, 1953) and the Gaussian plume model. 

The Gaussian plume model estimates the average pheromone flux by multiplying the measured odor concentration by mean wind speed, using the following formula (Elkinton etal, 1984). Everything is the same as in the Sutton model, except that ay and az, respectively, replace the terms Cy and Cz of the Sutton model. Dispersion coefficients are determined for each experiment separately. 

Water may be better than air for studying the dynamics of stimulus dispersal, because in this denser medium fluid dynamic processes are attenuated (Atema, 1988). As interindividual distances increase with increasing body size, pheromone communication becomes less and less practical in water, particularly because of signal delays, dilution, and cross-currents. 

Elkinton, J. S., Card6, R. T., and Mason, C. J. (1984). Evaluation of time-average dispersion models for estimating pheromone concentrations in a deciduous forest. Journal of Chemical Ecology 10,1081-1108. 

Diffusion is the gradual dispersal of one substance through another substance, such as one gas through another gas (Fig. 4.20). Diffusion explains the spread of perfumes and pheromones, the chemical signals between animals, through air. It also helps to keep the composition of the atmosphere approximately constant, because abnormally high concentra-... 

Ecological and behavioral considerations, especially with regard to dispersal and mating characteristics, may ultimately determine whether or not the use of pheromones is feasible and practical for a given insect species. 

Until a more detailed understanding of mating behavior, dispersal behavior and a complete identification of additional pheromone components is achieved, further field work on mating disruption with budworm can only proceed on an empirical basis. Additionally, treatment effects will be difficult to interpret unequivocally due to the local and long range movements of budworm adults into and out... 

Pheromones are powerful modulators of insect behavior. Since the isolation and identification of the first pheromone, (10E, 12Z)-hexadec-10,12-dien-l-ol, the sex attractant of the silk moth Bombyx mori, thousands of other insect pheromones have been identified. Our understanding of the sensory apparatus required for pheromone detection has also increased significantly. Coincidentally, B. mori was instrumental in many of these advances (see below). Volatile pheromones are detected by a specialized olfactory system localized on the antennae. The precise recognition of species-specific nuances in the structure and composition of pheromone components is essential for effective pheromone-based communication. The pheromone olfactory system of species studied so far exhibits remarkable selectivity towards the species-specific pheromone blend. Pheromones are emitted in low (fg-pg) quantities and are dispersed and greatly diluted in air plumes. Thus, pheromone olfaction systems are among the most sensitive chemosensory systems known. (Schneider et al., 1968). This chapter summarizes efforts (particularly over the past 10 years) to understand the molecular basis for the remarkable selectivity and sensitivity of the pheromone olfactory system in insects. The chapter will also outline efforts to design compounds that interfere with one or more of the early events in olfaction. 

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