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Pheromone-behavior under a Wide Range of Variables

Many investigators routinely anesthetize insects at one time or another during their adult life to facilitate differentiation of sexes, for transfer to fresh containers, or for various surgical operat...

Many investigators routinely anesthetize insects at one time or another during their adult life to facilitate differentiation of sexes, for transfer to fresh containers, or for various surgical operations. The possible effect of such anesthetization on pheromone behavior is rarely questioned. However, Brady and Smithwick (1968) found that treatment of female Indian meal moths with nitrogen, carbon dioxide, or ether vapors suppressed sex pheromone release for up to nine hours. Holding the females at a cold temperature of 8 C, which resulted in a high degree of immobilization, had no effect on subsequent male pheromone releasing behavior. More studies of this type are needed to determine how pheromones can be used in conjunction with other agents of insect control in pest management programs.

The control of sex pheromone-behavior obviously is not simple. Pheromone-behavior for men, like most other insect behavior, is probably precoded in a manner somewhat analogous to a computer program within a pheromone-behavior ‘center’ located in the central nervous system. Most of the time the behavior is not expressed because inhibitory messages arrive at the center over nervous system channels from some of the other, competing nervous system centers (such as the ‘feeding behavior center’ or ‘escape behavior center’). Also, most of the time inhibitory messages will arrive over some of the sensory channels that communicate the state of the outside environment and of the internal physiology of the insect. The details of the degree of control of pheromone-behavior exerted by each of the environmental and physiological variables discussed in this chapter vary from one species to the next. Some species exhibit pheromone-behavior under a wide range of variables and others may be restricted to a narrow range. The simultaneous action of the variables can be appreciated by a summary of some of the information presented in this chapter concerning male pheromone responsiveness in one species, the cabbage looper moth. Males respond optimally to female sex pheromone: 1) during a few specific hours of the night; 2) at a light intensity equivalent to moonlight or darker; 3) at a temperature above 12 C; 4) when the wind velocity is below male ight speed (about 3 m/sec); 5) when the male has reached the physiological age (about 2 days after emergence) so that sperm is available for mating; 6) when he has not mated already during that same dark period; and 7) when he has not been recently exposed to a high level of the pheromone. Any one of these restrictive conditions alone can entirely prevent his response to pheromone during some potential reproductive periods, as when the temperature does not exceed 12 C at the mechanisms of orientation to a distant pheromone source. This varies with pheromone effects.

Insects of many species utilize sex pheromones for recruiting mates. The pheromone is emitted by one sex, the sender, and transported through the air to a prospective mate, the receiver. If the receiver perceives an above threshold concentration of the pheromoneFeature Articles, it initiates a series of responses which eventually bring it to the vicinity of the source of the chemical.

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ABOUT THE AUTHOR


Alexander P is a blogger from Los Angeles that studies pheromones.



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