Insect behavioral compounds systems

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. 

Fabre tested this hypothesis and subsequently rejected the idea that electromagnetic radiation was involved in the sexual communication systems of moths however he remained skeptical of the involvement of the sense of smell. Sixty years later the case for smell was finally settled when German chemists, led by A. Butenandt (3-5), were the first to isolate, identify, and synthesize an insect sex pheromone, that of the female silkworm (Bombyx morl). They found that the compound responsible for eliciting sexual behavior from the male moth was ( E, Z)-10,12-hexadecadien-l-ol. 

Insects are the most diverse group animals on earth, with approximately five million species described to date (Novotny et al. 2002). Amidst this great diversity are adaptations common to all insects that maximize inclusive fitness in their respective habitats. One such fundamental adaptation is the ability to respond to cues in the environment, in particular the ability to detect external biological compounds via a chemical sensor. The sophisticated olfactory system of insects is able to sense volatile odorants derived from prey, host plants, and conspecific individuals. These compounds are detected by olfactory receptor neurons (ORNs) housed in the antennae, and these ORNs relay information about food sources, oviposition sites, and mates that leads to behavior based on neural responses mediated by the ORNs. The binding... 

The observation that both xylamine and desipramine are potent inhibitors of octopamine uptake and acetylation suggests that they, and their relatives, represent potential tools for the assessment of the suitability of these systems as a target for the development of novel insect control agents. Preliminary studies with xylamine injected into adult American cockroaches and adult tobacco budworms suggests that the activity is depressive rather than stimulatory. However, more detailed studies of the physiological and behavioral actions of these compounds are warranted. 

The sensitivity of pheromone perception in bark beetles appears to be generally typical of the very high sensitivity shown by many insects to their pheromones (Seabrook, 1978 Payne, 1979 see also Mustaparta, Chapter 2). In general, beetles have a lower threshold for their own pheromonal components than to other terpenes and related compounds (Mustaparta et al., 1979 Dickens, 1981). In I. pini, receptor cells specialized for pheromone perception respond minimally, if at all, to host compounds, and vice versa (Mustaparta et al., 1979,1980). However, the behavioral interruption of the response of I. pini to (- )ipsdienol by a few percent of (+ )ipsdienol or by ipsenol must be due to processing in the central nervous system of the insect and not to any interaction of compounds at the antennal receptor sites. Similarly, the synergistic effect of a pheromone blend is due to central integration. 

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