Insect behavioral compounds

See also Antimony (Sb) Indium (In) Insect behavior, compounds affecting, 14 345-346... 

Use of automated headspace SPDE/GC-MS not only enabled the identification in female African elephant urine of a number of known insect pheromones (compounds 2-6, Fig. 2.1), but also revealed the presence of the beetle biochemical precursors to frontalin (2), exo-brevicomin (3) and ent/o-brevicomin (4), thus suggesting a common biosynthetic pathway (Goodwin et al. 2006). Extensive behavioral bioassays must be performed to determine whether any of these compounds is functioning as a pheromone among African elephants. 

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. 

The external cuticle of insects is covered by a waxy layer composed of mixtures of hydro-phobic lipids that include long-chain alkanes, alkenes, wax esters, fatty acids, alcohols, aldehydes, and sterols. The primary purpose of this layer is to maintain water balance and prevent desiccation, as described in Chapter 6, but many of the cuticular lipid components have important secondary roles as intraspecific contact chemical signals (pheromones). These roles include species and sex recognition during reproductive interactions, and nestmate recognition and other colony organization functions in social insects. Thus, these compounds are essential mediators of insect behaviors. Cuticular compounds are also exploited by parasitoids and predators as interspecific contact cues (kairomones) to aid in host location. 

Compounds that alter insect behavior in other ways may also be useful e.g. chemicals that increase insect locomotor activity should enhance the uptake of pesticides from treated surfaces. Such compounds are already known among the formamidines insecticides and their relatives that stimulate octopamine receptors (12), and further research in this area of pest biochemistry could reveal other locomotor stimulators such as phosphodiesterase inhibitors. A... 

It was mentioned earlier in this chapter that alkaloids have no selective toxicity to invertebrates. Therefore, for many insects, these compounds are more attractive than toxins (Figure 4.5). The cases of butterfly or beetle behaviors just mentioned are very evident examples of the importance of plants for invertebrates. In both cases, alkaloids are secondary compounds that take part in the attraction for feeding. Moreover, it is also known that Manduca sexta flourish on alkaloid-rich Nicotiana plants and bmchid beetles BrucMdius villosus) on quinolizidine-alkaloid-iich plants.Such examples are a consequence of the herbivore model for choosing a specific plant diet. This model is based on the plant-herbivore interaction. The plant alone can either attract or deter the insect adult or larvae. It is necessary to highlight that alkaloids represent only one group of the secondary compounds through which plants worldwide interact with insects and other animals. 

The rapid growth of knowledge of natural products with biological activities toward pests now provides an option for treatment, a clearer understanding of biochemical mechanisms, and a basis for biorational approaches to the design of pest control agents Compounds that modify insect behavior are also valuable for pest control because they are normally not toxic to the target insect or to the environment ... 

Inscoe, M. N., and M. Beroza Analysis of pheromones and other compounds controlling insect behavior. In G. Zweig and J. Sherma, Eds., Analytical Methods for Pesticides and Plant Growth Regulators, Vol. VIII, Government Regulations, Pheromone Analysis, Additional Pesticides, p. 31—114. New York Academic Press. 1976. 

Chemical cues hold considerable promise for manipulating behavior in vertebrates, provided we understand an animal s natural history, biology, and behavior well. However, the development of chemical attractants, stimulants, inhibitors, and repellents for vertebrates has progressed rather slowly for several reasons. First, chemical stimulus and behavior are not connected as rigidly as in insects, for example. Second, the same stimulus may elicit different behaviors, depending on the state of the recipient and the context. Third, chemical cues often are rather complex mixtures of compounds. Fourth, learning, especially early experience plays a major role in vertebrate, notably mammalian behavior. Finally, many behaviors are modulated by several sensory modalities so that chemical stimuli alone trigger only incomplete responses at best. 

---