Insect pheromones semiochemicals

Fig-1 Schematic view of the overall olfactory processing in insects. Pheromones and other semiochemicals are detected by specialized sensilla on the antennae, where the chemical signal is transduced into nervous activity. The olfactory receptor neurons in the semiochemi-cal-detecting sensilla are connected directly to the antennal lobe. Here the semiochemical-derived electrical signals are processed and sent out (through projection neurons) to the protocerebrum. Olfactory information is then integrated with other stimulus modalities, a decision is made, and the motor system is told what to do... 

Recently, comprehensive World Wide Web (Internet) databases have been established on insect pheromones and semiochemicals The Pherolist , a database of chemicals identified from sex pheromone glands of female lepidopteran insects and other chemicals attractive to male moths (Am et al., 1999) and The Pherobase , a database of pheromones and semiochemicals for Lepidoptera and other insect orders (El-Sayed, 2006). These large databases on behavior modifying chemicals have extensive cross-linkages for animal taxa, indexes of compounds and source (reference) indexes. The indexes include those compounds cited in this chapter and many more with pheromone and semiochemical function acetate esters, diols, epoxides, ethers, ketones and secondary alcohols. For example, The Pherolist reports approximately 90 epoxy derivatives of C17-C23 of n-alkancs, mono-alkenes and di-alkenes as insect semiochemicals. 

El-Sayed, A. M. (2009). The Pherobase Database of Insect Pheromones and Semiochemicals. http //www.pherobase.com. 

Biochemical pesticides include, but are not limited to, products such as semiochemicals (e.g., insect pheromones), hormones (e.g., insect juvenile growth hormones), natural plant and insect regulators, and enzymes. When necessary the Agency will evaluate products on an individual basis to determine whether they are biochemical or conventional chemical pesticide. ... 

It was most timely that the only known mammalian semiochemicals which fit nicely into the concept of insect pheromones - two steroids present in the saliva of the domestic boar (5a-androst-16-en-3-one and 3a-hydroxy-5a-androst-16-ene) - were isolated by Patterson (1969), just at the time when interest in olfactory communication was rising. 

Prokopy, R. J. (1981a) Epideictic pheromones that influence spacing patterns of phytophagous insects. In Semiochemicals Their Role in Pest Control (Nordlund, D. A., Jones, R. L. and Lewis, W. J., eds) pp. 181-213. Wiley Press, New York. 

Steps in accomplishing the goal of utilizing pheromone semiochemicals from insects to control pests and invasive weeds include 1) establishing laboratory cultures of the insect species having economic impact on agriculture... 

The first volume ends with a chapter by G. Pohnert on chemical defence in the marine environment. Defense compounds, which can be regarded as allomones, are often, but not always, more complex than other semiochemicals and may have unique modes of action. The biological mechanisms are not always easy to unravel, which is shown by some of examples. The reader may be tempted to compare the chemical complexity with that of terrestrial insect defence, which can be found in the second volume chapter by D. Daloze and J.-C. Braekman. Insects thus do not only produce interesting pheromones, but also complex allelochemicals for their own protection. 

Abstract Hymenoptera is a very large and diverse insect order that includes the majority of both the social and the parasitic insects. With such diversity comes a variety and complexity of semiochemicals that reflect the varied biology of members of this order. This chapter reviews the chemical identification of pheromones and semiochemicals in the order Hymenoptera since 1990. For this review, the species in Hymenoptera have been classified as solitary, parasitic, or social. The chemical diversity of semiochemicals in Hymenoptera and future trends in pheromone identification are also discussed. 

All of the suborder Symphyta and many species in the superfamily Aculeata in the suborder Apocrita are solitary insects. Although not requiring the complex semiochemistry of parasitic or social insects, solitary insects employ pheromones for mating, territorial marking, and host marking. Unfortunately, very few of these have been chemically identified. The pheromones of sawflies and seed wasps were extensively reviewed in 1999 [ 14]. The semiochemicals recently identified in solitary hymenoptera, discussed below, are summarized in Table 2 and Fig. 1. 

Parasitic hymenoptera hold promise in integrated pest management schemes, because they parasitize many economically important insect pests in a species-and stage-selective manner. The pheromones and kairomones of the parasitic hymenoptera have been studied for a long time, and there are many examples where there is evidence of chemical mediation of parasitoid behavior. This review emphasizes work done since the last major reviews [11, 12, 42] and, where it is available, on the primary bioassay-guided chemical identification of the semiochemical (Fig. 2 and Tables 3 and 4). 

The repertoire of chemicals that can be used for communication is limited by the biosynthetic ability of the insect. Compared to other insect orders, pheromone biosynthesis in Hymenoptera has received little study [191]. However, the biosynthetic origins of chemically diverse hymenopteran semiochemicals likely include aromatic, fatty acid, and terpenoid pathways as well as simple modifications of host-derived precursors. Notable recent studies include the biosynthesis of the fatty acid components (2 )-9-oxodec-2-enoic acid 52 and (2 )-9-hydroxydec-2-enoic acid of the honeybee queen mandibular pheromone from octadecanoic acid [192,193], and the aliphatic alcohol and ester... 

Because the chemical signals (semiochemicals) are normally produced in minute amounts and diluted in the environment with a complex mixture of chemical compounds derived from a myriad of sources, the olfactory system in insects evolved as a remarkably selective and sensitive system, which approaches the theoretical limit for a detector. For example, it has been estimated that the male silkworm moth is able to distinguish within 1 s 170 nerve impulses generated by the female silkworm moth s sex pheromone from 1700 spontaneous nervous impulses [ 1 ], thus, operating on a remarkably low S/N ratio ... 

Largely, the insect detectors for pheromones and other semiochemicals are arrays of hair-like sensilla distributed over the surface of the antennae and palps. In some species, such as scarab beetles [3, 4] and the honeybee [5], semiochemicals are received by olfactory plates. The more ubiquitous hair-like sensilla typically consist of hollow cuticular hairs (10-400 pm long, 1-5 pm thick) innervated by one or several olfactory receptor cells (neurons) and three auxiliary cells [6]. 

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