Perception of Pheromones by Insects and Vertebrates

The pheromone communication system is very primitive and chemical communication among protozoan cells was an evolutionary step preliminary to the formation of metazoans (4, 8, 209, 210). It is suggestive that according to recent behavioral studies fetal rats may be sensitive to the odor quality of aminiotic fluid (211). 

A mathematical model for the transmission of a chemical signal has been developed by Bossert and Wilson (2). According to this model, the substance is transmitted through the air in accordance with simple laws of diffusion when the air is still and the substance cannot adsorb on or react with other substances. At any point away from the emitter, pheromone concentration is a function of 1) the rate of molecular emission, 2) the diffusion coefficient of the substance, 3) the distance from the source and 4) the time from the initiation of the emission. 

The perception of pheromones by insects and vertebrates is a matter of several reviews and discussions 212-239). Hypotheses attempting to explain changes in the odor of organic molecules with changes in molecular structure and with spatial arrangement of the atoms, and to explain the effect of chirality on odor perception have been advanced by several authors 212, 216, 219, 223, 238). Other theories are based on vibrational energy levels of the molecules, intermolecular interactions and molecular shape and size 219, 220, 222, 233, 239). 

Insects detect pheromones in surprisingly small amounts. Thus, male Bombyx mori begin to react when air contains as little as 100 molecules of the female sex pheromone per cm 210). The trail pheromone of the leaf cutting ant Atta texana, methyl-4-methyl-pyrrole-2-carboxyl-ate (46) is perceived at a concentration of 0,08 pg/cm, that is 3.48 molecules/cm 240), about the same as that recorded for the trail pheromone cw-3-cw-6-/ran5-8-dodecatrien-l-ol of Reticulitermes virgin-icus termite workers (47) 241). 

It has long been known that pheromones in insects are detected by means of organs located in the antennae, but chemoreceptors have also been found in the tips of maxillary and labial palps, in the buccal cavity, in the epipharynx and at the inner face of the chpeolabrum 217). 

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