- Email: [email protected]
Pheromones
Ecotoxicology | Pheromones Gupta AP and Lewontin R (1982) A study of reaction norms in natural populations of Drosophila pseudoobscura. Evolution 36: 934–948. Ketterson ED and Nolan V, Jr. (1992) Hormones and life histories: An integrative approach. American Naturalist 140: S33–S62. Mitchell SD (1990) The units of behavior in evolutionary explanation. In: Bekoff M and Jamieson D (eds.) Interpretation and Explanation in the Study of Animal Behavior, vol. II, pp. 63–83. Boulder, CO: Westview Press. Otte D (1972) Simple versus elaborate behavior in grasshoppers. Analysis of communication in the genus Syrbula. Behaviour 42: 291–322. Page RE, Jr., Scheiner R, Erber J, and Amdam GV (2006) The development and evolution of division of labor and foraging
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specialization in a social insect (Apis mellifera L.). Current Topics in Developmental Biology 74: 253–286. Scharloo W (1989) Developmental and physiological aspects of reaction norms. BioScience 39: 465–471. Schlichting CD and Pigliucci M (1998) Phenotypic Evolution. A Reaction Norm Perspective. Sunderland: Sinauer Associates. Sih A (2004) A behavioral ecological view of phenotypic plasticity. In: DeWitt TJ and Scheiner SM (eds.) Phenotypic Plasticity: Functional and Conceptual Approaches, pp. 112–125. Oxford: Oxford University Press. Wenzel JW (1992) Behavioral homology and phylogeny. Annual Review of Ecology and Systematics 23: 361–381. West-Eberhard MJ (2003) Developmental Plasticity and Evolution. New York: Oxford University Press.
Pheromones O Anderbrant, Lund University, Lund, Sweden ª 2008 Elsevier B.V. All rights reserved.
Further Reading
Pheromones, from Greek pherein, to transfer, and hormon, to excite, are intraspecific chemical signals, first defined in 1959 as ‘‘substances secreted to the outside by an individual and received by a second individual of the same species in which they release a specific reaction, for instance a defined behaviour (releaser pheromone) or developmental process (primer pheromone).’’ Since the first chemical characterization of a pheromone in 1959, pheromones have been identified, or at least proved to exist, in a couple of thousand species, terrestrial as well as aquatic. Pheromones can release a variety of behaviors in the receiving individual and often they are specified according to their function, for example, sex pheromone (mate attraction or other reproductive behavior – usually sex specific), aggregation pheromone (attraction of both sexes to a common resource), alarm pheromone (common in social insects), and hostmarking or oviposition-deterring pheromones. A pheromone may consist of a single substance (e.g., some alarm pheromones in social insects, transferring comparatively simple messages) or usually a blend of several compounds in a more or less specific ratio (most sex pheromones, where specificity is important). The chemical nature of the compounds varies depending on their origin and biosynthesis and covers several classes of chemicals. Several hundred different substances have been shown to elicit pheromone activity. Some substances are synthesized de novo by the emitting individual via primary biosynthetic pathways, whereas others may originate from compounds obtained through the food. The size and structure of the molecules involved are important for the function of the pheromone. In terrestrial
species, pheromones are often used for transferring messages over relatively large distances, typically 10–100 m, which means that the compounds constituting the pheromone have to be volatile. On the other hand, less-volatile compounds will remain for longer periods where they are released or deposited, which might be a desired character of, for example, host-marking pheromones or pheromones defining a territory border. In moths (Lepidoptera), the most-studied group of insects from a pheromone perspective, the typical pheromone consists of two to four straight-chain fatty-acid derivatives, 10–18 carbon atoms long, with one or two double bonds and different functional groups, such as alcohol, ester, or aldehyde. Such long-chain molecules may also appear as ketones or epoxides. The biochemical basis of these moth pheromones is found in the fatty acid biosynthesis pathway. Many pheromone substances have a regularly branched carbon skeleton and several of these are terpenoid compounds, biosynthesized through the intermediate mevalonic acid. These terpenoid substances are built up by linking two or more isoprene (five-carbon) units. Yet other pheromone components are cyclic with carbons only in the ring or heterocyclic containing oxygen or nitrogen. Also polycyclic pheromone compounds exist. Many of the compounds identified from pheromones can exist in different structural forms, the so-called isomers. For instance, the double bonds in the carbon chain can be in different places (positional isomers) or the double bond is locking the molecule so that two different geometric isomers can exist. When a carbon atom binds to four different ligands (atoms or parts of molecule), we talk about optical isomers. The fate of the
2708 Ecotoxicology | Pheromones
released pheromone molecules in the environment depends on their structure. Some are oxidized and others are sensitive to ultraviolet (UV) light and break down into more simple structures. Pheromones usually show a high degree of species specificity, with few ‘errors’ made, although they might be exploited by natural enemies that have evolved capability to detect them. Furthermore, they are often produced and released in minute amounts, in insects typically 1–100 ng per day, and in correspondence to a sensitive and finely tuned detection apparatus in the receiving individual. Several of the above-mentioned characteristics have made pheromones tractable for use in management of pest organisms, in particular insects. Pheromones are usually species specific, active at very low concentration, affecting critical steps in the life cycle such as mate finding or oviposition, and consist of naturally occurring, degradable, and nontoxic compounds. A disadvantage in connection to practical application is that each target species requires a new scientific effort in order to characterize the pheromone and sometimes also to synthesize it. Pheromones are used for various purposes in pest management. For detection and monitoring. A trap is equipped with a dispenser (release device) loaded with the synthesized pheromone and attracts individuals of the target species. Since attraction is the key behavioral element for a trap to work, only sex and aggregation pheromones can be used for this purpose. The type of trap, trap position, dispenser, and release rate to be used vary among species, purpose, and habitat. Attractive traps may answer questions such as where, when, and how many. The first question may be relevant for mapping the distribution range or for detection of alien and potentially invasive species. Answers to the second question can be useful when timing treatments to control the target species and the third question is important when estimating population densities or establishing thresholds for future control. Pheromone-based attractive traps are commercially available for several hundred different insect species, notably moths and beetles, and are used on a large scale in forestry, agriculture, and for indoor pests. For population control. Several methods have been developed to be able to manipulate a large-enough proportion of a population to affect its future damage potential. In essence, two strategies have been followed, one known as mass trapping, including attract and kill, and a second called mating disruption or confusion. Mass trapping: The idea with this strategy is to catch as many individuals as possible in order to reduce the population below a level where it does not cause any harm. To date this has mainly been used against species using an aggregation pheromone resulting in catch of both sexes. Bark beetles infesting conifers in the northern temperate region have been subject to large-scale mass-trapping attempts. Mass trapping using sex-specific pheromones
(e.g., female-produced sex pheromones in moths) is limited by the fact that most male moths can mate many times, and even with an efficient mass-trapping system the few nontrapped males may copulate with a large fraction of the females. ‘Attract and kill’ is a variant in which the pheromone is combined with a poison (e.g., an insecticide) which kills the attracted specimens. In this case no container or other device to catch the attracted individuals is needed. Mating disruption: This method is used against species with sex pheromones, usually female-produced. The mate-finding behavior in males is disturbed or disrupted by the release of relatively large amounts of synthetic female sex pheromone (typically 100 g ha1, effective over a period from weeks to a whole season). By sensing the smell of female ‘‘everywhere’’ the male is unable to find his way to the females, he is ‘‘confused.’’ This leads to fewer matings within the treated area, fewer offspring, and less damage. Mating disruption is used on a large scale, that is, hundreds of thousands of hectares, against gypsy moths in North America and fruit and grape pests in many parts of the world. Other pheromone-based methods include the pushpull strategy, in which an attractive pheromone is combined with a repulsive chemical signal in order to direct the target species to an area where it can be handled more easily. From an ecotoxicological point of view, effects of pheromones have not received much attention so far and no ecotoxicological side effects have been reported. The reason for this is quite obvious considering the nontoxic chemical structures of most pheromone molecules, their degradability, and the small quantities in which they are used. A few reports exist in which a behavioral effect on the target species has been recorded after the pheromone dispensers have been removed. These reports are from mating-disruption treatments and presumably some pheromone has been adsorbed on plants or other material and released later on. Two risk factors, though not ecotoxicological, are worth taking into consideration during repeated and long-lasting treatment with pheromones. First, there is a theoretical possibility of resistance development, that is, individuals with a pheromone deviating from that used in the treatment will be favored because they escape masstrapping or mating disruption. However, this can be monitored and the synthetic pheromone composition altered when necessary. Second, nontarget species may be trapped and killed. This is most likely to hit natural enemies of the species in focus, but can sometimes be avoided by modifying, for instance, the trap design. The use of pheromones in pest control, and possibly also in conservation biology, can be expected to increase worldwide in the future. An increased need for environmentally acceptable, albeit effective, pest control methods points toward use of various biologically based rather than traditional chemical methods. Pheromones and
Philosophy of Ecology | Philosophy of Ecology: Overview
other semiochemicals (information-carrying chemicals, also including those transferring messages between species) provide one such strategy. See also: Chemical Communication.
Further Reading Agosta WC (1992) Chemical Communication: The Language of Pheromones. San Francisco: Scientific Library, W.H. Freeman. Anon (2003) Insect Pheromones: Mastering Communication to Control Pests. National Academy of Sciences, USA. http:// www.beyonddiscovery.org/content/view.article.asp?a ¼ 2702 (accessed January 2008).
2709
Blomquist GJ and Vogt RG (eds.) (2003) Insect Pheromone Biochemistry and Molecular Biology, 745pp. Amsterdam: Elsevier. Carde´ RT and Minks AK (eds.) (1997) Insect Pheromone Research, New Directions, 684pp. New York: Chapman and Hall. El-Sayed AM (2005) The Pherobase: Database of Insect Pheromones and Semiochemicals; http://www.pherobase.com/ (accessed January 2008). Hardie J and Minks AK (eds.) (1999) Pheromones of Non-Lepidopteran Insects Associated with Agricultural Plant, 466pp. Wallingford: CABI Publishing. Howse P, Stevens I, and Jones J (1998) Insect Pheromones and Their Use in Pest Management, 369pp. London: Chapman and Hall. Witzgall P, Lindblom T, Bengtsson M, and To´th M (2004) The Pherolist. http://www-pherolist.slu.se/pherolist.php (accessed January 2008). Wyatt TD (2003) Pheromones and Animal Behaviour, Communication by Smell and Taste, 391pp. Cambridge: Cambridge University Press.
Philosophy of Ecology: Overview K deLaplante, Iowa State University, Ames, IA, USA ª 2008 Elsevier B.V. All rights reserved.
Introduction Ecology: The Study of Ecological Phenomena Two Conceptions of the Domain of Ecology Issues in the Philosophy of Ecology: Restrictive Mode
Issues in the Philosophy of Ecology: Expansive Mode Ecology-the-Science and Ecology-the-Worldview Further Reading
Introduction
ameliorate humanity’s dysfunctional relationship with nature (deep ecology, social ecology, socialist ecology, ecofeminism, etc.). Do all of these philosophies count as philosophies of ecology? Are they all branches of the philosophy of ecology? Within academic philosophy, the most common approach to this question tries to draw a distinction between ecological science and the ethical, social, and broader philosophical uses of the term. Proponents of this approach reserve the term ‘philosophy of ecology’ for the philosophical study of ecological science qua science, with a focus on conceptual issues in fields like behavioral ecology, population ecology, community ecology, evolutionary ecology, and ecosystem ecology. On this view, ecology is conceived as a branch of the natural, biological sciences, and the philosophy of ecology as a specialization within the philosophy of science. Though they may occasionally appeal to the ecological sciences for intellectual support for their various philosophical positions, deep ecology, social ecology, and other radical ecophilosophies are regarded as branches of social theory or environmental philosophy, not the philosophy of ecology. The approach just described has much to recommend it, but the conception of the philosophy of ecology that will be developed in this article takes a somewhat different tack, one that endorses a broader conception of both
At its most general level, the philosophy of ecology is the philosophical study of (1) ecological phenomena and (2) those disciplines that study ecological phenomena. This definition has certain virtues, but it lacks content until we specify what we mean by ‘ecological phenomena’ and what sorts of disciplines study such phenomena. The task is complicated by the fact that the term ‘ecology’ is used in different ways in different contexts. Ecology is of course a science, but ecology is also identified with a broader philosophical and ethical worldview that in various respects predates modern ecological science. In the ‘romantic ecology’ of the nineteenth century associated with writers like Wordsworth, Thoreau, and Emerson, it was associated with a rejection of mechanistic, atomistic, and reductionistic science and philosophy that was believed to be responsible for a variety of human and natural ills. This conception carried over into the ‘ecology movement’ of the 1960s, an environmental movement tied to broader sociocultural movements of that decade (women’s liberation, civil rights, and a range of anticonsumerist, anticapitalist, and antimilitarist movements). In recent decades the term has been appropriated by a number of sociopolitical movements and philosophies that seek to diagnose and
2707
specialization in a social insect (Apis mellifera L.). Current Topics in Developmental Biology 74: 253–286. Scharloo W (1989) Developmental and physiological aspects of reaction norms. BioScience 39: 465–471. Schlichting CD and Pigliucci M (1998) Phenotypic Evolution. A Reaction Norm Perspective. Sunderland: Sinauer Associates. Sih A (2004) A behavioral ecological view of phenotypic plasticity. In: DeWitt TJ and Scheiner SM (eds.) Phenotypic Plasticity: Functional and Conceptual Approaches, pp. 112–125. Oxford: Oxford University Press. Wenzel JW (1992) Behavioral homology and phylogeny. Annual Review of Ecology and Systematics 23: 361–381. West-Eberhard MJ (2003) Developmental Plasticity and Evolution. New York: Oxford University Press.
Pheromones O Anderbrant, Lund University, Lund, Sweden ª 2008 Elsevier B.V. All rights reserved.
Further Reading
Pheromones, from Greek pherein, to transfer, and hormon, to excite, are intraspecific chemical signals, first defined in 1959 as ‘‘substances secreted to the outside by an individual and received by a second individual of the same species in which they release a specific reaction, for instance a defined behaviour (releaser pheromone) or developmental process (primer pheromone).’’ Since the first chemical characterization of a pheromone in 1959, pheromones have been identified, or at least proved to exist, in a couple of thousand species, terrestrial as well as aquatic. Pheromones can release a variety of behaviors in the receiving individual and often they are specified according to their function, for example, sex pheromone (mate attraction or other reproductive behavior – usually sex specific), aggregation pheromone (attraction of both sexes to a common resource), alarm pheromone (common in social insects), and hostmarking or oviposition-deterring pheromones. A pheromone may consist of a single substance (e.g., some alarm pheromones in social insects, transferring comparatively simple messages) or usually a blend of several compounds in a more or less specific ratio (most sex pheromones, where specificity is important). The chemical nature of the compounds varies depending on their origin and biosynthesis and covers several classes of chemicals. Several hundred different substances have been shown to elicit pheromone activity. Some substances are synthesized de novo by the emitting individual via primary biosynthetic pathways, whereas others may originate from compounds obtained through the food. The size and structure of the molecules involved are important for the function of the pheromone. In terrestrial
species, pheromones are often used for transferring messages over relatively large distances, typically 10–100 m, which means that the compounds constituting the pheromone have to be volatile. On the other hand, less-volatile compounds will remain for longer periods where they are released or deposited, which might be a desired character of, for example, host-marking pheromones or pheromones defining a territory border. In moths (Lepidoptera), the most-studied group of insects from a pheromone perspective, the typical pheromone consists of two to four straight-chain fatty-acid derivatives, 10–18 carbon atoms long, with one or two double bonds and different functional groups, such as alcohol, ester, or aldehyde. Such long-chain molecules may also appear as ketones or epoxides. The biochemical basis of these moth pheromones is found in the fatty acid biosynthesis pathway. Many pheromone substances have a regularly branched carbon skeleton and several of these are terpenoid compounds, biosynthesized through the intermediate mevalonic acid. These terpenoid substances are built up by linking two or more isoprene (five-carbon) units. Yet other pheromone components are cyclic with carbons only in the ring or heterocyclic containing oxygen or nitrogen. Also polycyclic pheromone compounds exist. Many of the compounds identified from pheromones can exist in different structural forms, the so-called isomers. For instance, the double bonds in the carbon chain can be in different places (positional isomers) or the double bond is locking the molecule so that two different geometric isomers can exist. When a carbon atom binds to four different ligands (atoms or parts of molecule), we talk about optical isomers. The fate of the
2708 Ecotoxicology | Pheromones
released pheromone molecules in the environment depends on their structure. Some are oxidized and others are sensitive to ultraviolet (UV) light and break down into more simple structures. Pheromones usually show a high degree of species specificity, with few ‘errors’ made, although they might be exploited by natural enemies that have evolved capability to detect them. Furthermore, they are often produced and released in minute amounts, in insects typically 1–100 ng per day, and in correspondence to a sensitive and finely tuned detection apparatus in the receiving individual. Several of the above-mentioned characteristics have made pheromones tractable for use in management of pest organisms, in particular insects. Pheromones are usually species specific, active at very low concentration, affecting critical steps in the life cycle such as mate finding or oviposition, and consist of naturally occurring, degradable, and nontoxic compounds. A disadvantage in connection to practical application is that each target species requires a new scientific effort in order to characterize the pheromone and sometimes also to synthesize it. Pheromones are used for various purposes in pest management. For detection and monitoring. A trap is equipped with a dispenser (release device) loaded with the synthesized pheromone and attracts individuals of the target species. Since attraction is the key behavioral element for a trap to work, only sex and aggregation pheromones can be used for this purpose. The type of trap, trap position, dispenser, and release rate to be used vary among species, purpose, and habitat. Attractive traps may answer questions such as where, when, and how many. The first question may be relevant for mapping the distribution range or for detection of alien and potentially invasive species. Answers to the second question can be useful when timing treatments to control the target species and the third question is important when estimating population densities or establishing thresholds for future control. Pheromone-based attractive traps are commercially available for several hundred different insect species, notably moths and beetles, and are used on a large scale in forestry, agriculture, and for indoor pests. For population control. Several methods have been developed to be able to manipulate a large-enough proportion of a population to affect its future damage potential. In essence, two strategies have been followed, one known as mass trapping, including attract and kill, and a second called mating disruption or confusion. Mass trapping: The idea with this strategy is to catch as many individuals as possible in order to reduce the population below a level where it does not cause any harm. To date this has mainly been used against species using an aggregation pheromone resulting in catch of both sexes. Bark beetles infesting conifers in the northern temperate region have been subject to large-scale mass-trapping attempts. Mass trapping using sex-specific pheromones
(e.g., female-produced sex pheromones in moths) is limited by the fact that most male moths can mate many times, and even with an efficient mass-trapping system the few nontrapped males may copulate with a large fraction of the females. ‘Attract and kill’ is a variant in which the pheromone is combined with a poison (e.g., an insecticide) which kills the attracted specimens. In this case no container or other device to catch the attracted individuals is needed. Mating disruption: This method is used against species with sex pheromones, usually female-produced. The mate-finding behavior in males is disturbed or disrupted by the release of relatively large amounts of synthetic female sex pheromone (typically 100 g ha1, effective over a period from weeks to a whole season). By sensing the smell of female ‘‘everywhere’’ the male is unable to find his way to the females, he is ‘‘confused.’’ This leads to fewer matings within the treated area, fewer offspring, and less damage. Mating disruption is used on a large scale, that is, hundreds of thousands of hectares, against gypsy moths in North America and fruit and grape pests in many parts of the world. Other pheromone-based methods include the pushpull strategy, in which an attractive pheromone is combined with a repulsive chemical signal in order to direct the target species to an area where it can be handled more easily. From an ecotoxicological point of view, effects of pheromones have not received much attention so far and no ecotoxicological side effects have been reported. The reason for this is quite obvious considering the nontoxic chemical structures of most pheromone molecules, their degradability, and the small quantities in which they are used. A few reports exist in which a behavioral effect on the target species has been recorded after the pheromone dispensers have been removed. These reports are from mating-disruption treatments and presumably some pheromone has been adsorbed on plants or other material and released later on. Two risk factors, though not ecotoxicological, are worth taking into consideration during repeated and long-lasting treatment with pheromones. First, there is a theoretical possibility of resistance development, that is, individuals with a pheromone deviating from that used in the treatment will be favored because they escape masstrapping or mating disruption. However, this can be monitored and the synthetic pheromone composition altered when necessary. Second, nontarget species may be trapped and killed. This is most likely to hit natural enemies of the species in focus, but can sometimes be avoided by modifying, for instance, the trap design. The use of pheromones in pest control, and possibly also in conservation biology, can be expected to increase worldwide in the future. An increased need for environmentally acceptable, albeit effective, pest control methods points toward use of various biologically based rather than traditional chemical methods. Pheromones and
Philosophy of Ecology | Philosophy of Ecology: Overview
other semiochemicals (information-carrying chemicals, also including those transferring messages between species) provide one such strategy. See also: Chemical Communication.
Further Reading Agosta WC (1992) Chemical Communication: The Language of Pheromones. San Francisco: Scientific Library, W.H. Freeman. Anon (2003) Insect Pheromones: Mastering Communication to Control Pests. National Academy of Sciences, USA. http:// www.beyonddiscovery.org/content/view.article.asp?a ¼ 2702 (accessed January 2008).
2709
Blomquist GJ and Vogt RG (eds.) (2003) Insect Pheromone Biochemistry and Molecular Biology, 745pp. Amsterdam: Elsevier. Carde´ RT and Minks AK (eds.) (1997) Insect Pheromone Research, New Directions, 684pp. New York: Chapman and Hall. El-Sayed AM (2005) The Pherobase: Database of Insect Pheromones and Semiochemicals; http://www.pherobase.com/ (accessed January 2008). Hardie J and Minks AK (eds.) (1999) Pheromones of Non-Lepidopteran Insects Associated with Agricultural Plant, 466pp. Wallingford: CABI Publishing. Howse P, Stevens I, and Jones J (1998) Insect Pheromones and Their Use in Pest Management, 369pp. London: Chapman and Hall. Witzgall P, Lindblom T, Bengtsson M, and To´th M (2004) The Pherolist. http://www-pherolist.slu.se/pherolist.php (accessed January 2008). Wyatt TD (2003) Pheromones and Animal Behaviour, Communication by Smell and Taste, 391pp. Cambridge: Cambridge University Press.
Philosophy of Ecology: Overview K deLaplante, Iowa State University, Ames, IA, USA ª 2008 Elsevier B.V. All rights reserved.
Introduction Ecology: The Study of Ecological Phenomena Two Conceptions of the Domain of Ecology Issues in the Philosophy of Ecology: Restrictive Mode
Issues in the Philosophy of Ecology: Expansive Mode Ecology-the-Science and Ecology-the-Worldview Further Reading
Introduction
ameliorate humanity’s dysfunctional relationship with nature (deep ecology, social ecology, socialist ecology, ecofeminism, etc.). Do all of these philosophies count as philosophies of ecology? Are they all branches of the philosophy of ecology? Within academic philosophy, the most common approach to this question tries to draw a distinction between ecological science and the ethical, social, and broader philosophical uses of the term. Proponents of this approach reserve the term ‘philosophy of ecology’ for the philosophical study of ecological science qua science, with a focus on conceptual issues in fields like behavioral ecology, population ecology, community ecology, evolutionary ecology, and ecosystem ecology. On this view, ecology is conceived as a branch of the natural, biological sciences, and the philosophy of ecology as a specialization within the philosophy of science. Though they may occasionally appeal to the ecological sciences for intellectual support for their various philosophical positions, deep ecology, social ecology, and other radical ecophilosophies are regarded as branches of social theory or environmental philosophy, not the philosophy of ecology. The approach just described has much to recommend it, but the conception of the philosophy of ecology that will be developed in this article takes a somewhat different tack, one that endorses a broader conception of both
At its most general level, the philosophy of ecology is the philosophical study of (1) ecological phenomena and (2) those disciplines that study ecological phenomena. This definition has certain virtues, but it lacks content until we specify what we mean by ‘ecological phenomena’ and what sorts of disciplines study such phenomena. The task is complicated by the fact that the term ‘ecology’ is used in different ways in different contexts. Ecology is of course a science, but ecology is also identified with a broader philosophical and ethical worldview that in various respects predates modern ecological science. In the ‘romantic ecology’ of the nineteenth century associated with writers like Wordsworth, Thoreau, and Emerson, it was associated with a rejection of mechanistic, atomistic, and reductionistic science and philosophy that was believed to be responsible for a variety of human and natural ills. This conception carried over into the ‘ecology movement’ of the 1960s, an environmental movement tied to broader sociocultural movements of that decade (women’s liberation, civil rights, and a range of anticonsumerist, anticapitalist, and antimilitarist movements). In recent decades the term has been appropriated by a number of sociopolitical movements and philosophies that seek to diagnose and