Pheromone production regulation

Pheromone production regulated by gland development and cellular plasticity... 

Abstract Pheromones are utilized by many insects in a complex chemical communication system. This review will look at the biosynthesis of sex and aggregation pheromones in the model insects, moths, flies, cockroaches, and beetles. The biosynthetic pathways involve altered pathways of normal metabolism of fatty acids and isoprenoids. Endocrine regulation of the biosynthetic pathways will also be reviewed for the model insects. A neuropeptide named pheromone biosynthesis activating neuropeptide regulates sex pheromone biosynthesis in moths. Juvenile hormone regulates pheromone production in the beetles and cockroaches, while 20-hydroxyecdysone regulates pheromone production in the flies. 

The role of the nervous system in pheromone biosynthesis in moths is not clearly understood. Christensen and co-workers [208-211] proposed that the neurotransmitter octopamine may be involved as an intermediate messenger during the stimulation of sex pheromone production in H. virescens. These workers suggested that octopamine was involved in the regulation of pheromone production and that PBAN s role lies in the stimulation of octopamine release at nerve endings. However, contradicting results concerning octopa-mine-stimulated pheromone production were reported in the same species as well as other moth species [163,172,212-214]. 

It appears that, in beetles, pheromone production is regulated by JH III, despite the variations in biosynthetic pathways. JH apparently regulates pheromone production in beetles that utilize both fatty acid and isoprenoid biosynthetic pathways [8,98]. Environmental and physiological factors will in turn regulate production of JH. The endocrine regulation of pheromone production in the beetles has been best studied with regard to the bark beetles. 

The evidence for 20-hydroxyecdysone stimulating sex pheromone production in the housefly comes from both direct and indirect studies. A correlation was found between ovarian development and sex pheromone production in female flies [236,237]. Surgical removal of ovaries immediately after adult emergence resulted in no sex pheromone production, whereas allatectomized (which removes the source of JH production) females produced the same amount of pheromone as did normal females [238,239]. Additionally, ovariectomized females that received ovary implants produced sex pheromone [238]. These data demonstrate that 20-hydroxyecdysone and not JH regulates pheromone production in the housefly [111]. 

Additional evidence came from the finding that sex pheromone production could be stimulated in male houseflies that do not normally produce detectable sex pheromone components. Male houseflies were found to have longer chain alkenes, Z9-27 H,but did not have Z9-23 H. Implantation of ovaries into male houseflies resulted in a change in hydrocarbon biosynthesis such that the longer chain alkenes were not made but rather they produced the shorter chain length Z9-23 H [240]. Likewise, injection of 20-hydroxyecdysone into males induced sex pheromone production in a dose-dependent manner. These studies demonstrated that males possess the biosynthetic capability to produce sex pheromone, but normally do not produce the 20-hydroxyecdysone necessary to induce sex pheromone production. Males became an excellent model in which to study the hormonal regulation of pheromone biosynthesis in the housefly. 

Another aspect of the sex pheromone communication system concerns the endogenous signals that control pheromone production and release from the emitting insect. A number of hormones have been found to be involved in the control of pheromone production in various insect species (18). Juvenile hormone was found to induce vitellogenesis and sex pheromone production in some cockroach and beetle species. However, ecdysteroids were found to be involved in regulating reproductive processes, including vitellogenin synthesis, in dipteran species. 

In moths, it was discovered in Helicoverpa zea that a peptide produced in the subesophageal ganglion portion of the brain complex regulates pheromone production in female moths (19). This factor has been purified and characterized in three species, Helicoverpa zea (20), Bombyx mori (21, 22), and Lymantria dispar (23). They are all a 33- or 34-amino acid peptide (named pheromone biosynthesis activating neuropeptide, PBAN) and have in common an amidated C-terminal 5-amino acid sequence (FXPRL-amide), which is the minimum peptide fragment required for pheromon-tropic activity. In the redbanded leafroller moth, it was shown that PBAN from the brain stimulates the release of a different peptide from the bursae copulatrix that is used to stimulate pheromone production in the pheromone gland found at the posterior tip of the abdomen (24). 

The biosynthesis and endocrine regulation of pheromone production in beetles has been reviewed [33, 34]. Nevertheless, some more general pathways will be briefly discussed here. As corresponding structures are widespread among insects [2], the examples shown here are selected mostly from taxa other than beetles. Structures representing beetle pheromones will be shown in the context of the discussion of the corresponding species. 

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