蛾类昆虫性信息素受体及其作用机理

蛾类昆虫性信息素受体首先从烟芽夜蛾Heliothis virescens和家蚕Bombyx mori中鉴定出来, 到目前为止已经克隆得到了19种蛾类昆虫的几十种性信息素受体基因, 并且这些基因在系统发育树中聚成一个亚群。性信息素受体从蛾类蛹期开始表达, 主要表达在雄性触角的毛形感器中, 少部分受体在雌性触角、 雄性触角其他感器以及身体其他部位中也有表达。大部分蛾类性信息素受体的配体并不是单一的, 而是能够对多种性信息素组分有反应, 部分性信息素受体还能够识别性信息素以外的其他物质, 还有一部分性信息素受体的识别配体目前尚不清楚。另外发现在雌性蛾类触角中也存在一些嗅觉受体能够识别雄性分泌的性信息素。在蛾类性信息素受体与性信息素识别的过程中, 性信息素结合蛋白不仅能够特异性地运送配体到嗅觉神经元树状突上, 还能够提高性信息素与性信息素受体之间的结合效率。另外, OrCo类受体与性信息素受体共表达在嗅觉神经元中, 在蛾类性信息素受体与配体的识别过程中扮演了重要角色。但是蛾类信息素对神经元刺激的终止并非由性信息素受体控制, 而是由细胞中的气味降解酶等其他因子调控。蛾类性信息素受体研究中还有很多疑问需要解答, 其过程可能比我们想象的更为复杂。     

A flux capacitor for moth pheromones

In this issue of Chemical Senses, Baker et al. propose a provocative and intriguing explanation for a commonly observed phenomenon in moth chemocommunication. Sex pheromones in moths typically consist of mixtures of long-chain unsaturated compounds in specific ratios. These ratios are correspondingly detected by male moths using separate olfactory sensory neurons for each pheromone component housed singly or multiply in long trichoid sensilla on the antennal surface. These neurons are often present in different proportions, typically with the neuron responding to the highest ratio component present in greatest abundance or with the largest dendritic diameter. In their article, Baker et al. postulate that these physical differences in neuron magnitudes arise to compensate for the higher molecular flux present with the most abundant pheromone components. Such a suggestion raises several questions concerning the physiological and behavioral nature of pheromone communication. Specifically, is the flux in a natural pheromone plume high enough to warrant increased flux detection for the most abundant components? Second, how can changes in neuronal number or size lead to increased flux detection? And finally, how would this increased flux detection be accomplished at molecular, cellular, and ultimately network scales? We address each of these questions and propose future experiments that could offer insight into the stimulating proposition raised by Baker et al.     

Excitatory local circuits and their implications for olfactory processing in the fly antennal lobe

Conflicting views exist of how circuits of the antennal lobe, the insect equivalent of the olfactory bulb, translate input from olfactory receptor neurons (ORNs) into projection-neuron (PN) output. Synaptic connections between ORNs and PNs are one-to-one, yet PNs are more broadly tuned to odors than ORNs. The basis for this difference in receptive range remains unknown. Analyzing a Drosophila mutant lacking ORN input to one glomerulus, we show that some of the apparent complexity in the antennal lobe's output arises from lateral, interglomerular excitation of PNs. We describe a previously unidentified population of cholinergic local neurons (LNs) with multiglomerular processes. These excitatory LNs respond broadly to odors but exhibit little glomerular specificity in their synaptic output, suggesting that PNs are driven by a combination of glomerulus-specific ORN afferents and diffuse LN excitation. Lateral excitation may boost PN signals and enhance their transmission to third-order neurons in a mechanism akin to stochastic resonance.     

Morphometric modeling of olfactory circuits in the insect antennal lobe: I. Simulations of spiking local interneurons.

Inhibitory local interneurons (LNs) play a critical role in shaping the output of olfactory glomeruli in both the olfactory bulb of vertebrates and the antennal lobe of insects and other invertebrates. In order to examine how the complex geometry of LNs may affect signaling in the antennal lobe, we constructed detailed multi-compartmental models of single LNs from the sphinx moth, Manduca sexta, using morphometric data from confocal-microscopic images. Simulations clearly revealed a directionality in LNs that impeded the propagation of injected currents from the sub-micron-diameter glomerular dendrites toward the much larger-diameter integrating segment (IS) in the coarse neuropil. Furthermore, the addition of randomly-firing synapses distributed across the LN dendrites (simulating the noisy baseline activity of afferent input recorded from LNs in the odor-free state) led to a significant depolarization of the LN. Thus the background activity typically recorded from LNs in vivo could influence synaptic integration and spike transformation in LNs through voltage-dependent mechanisms. Other model manipulations showed that active currents inserted into the IS can help synchronize the activation of inhibitory synapses in glomeruli across the antennal lobe. These data, therefore, support experimental findings suggesting that spiking inhibitory LNs can operate as multifunctional units under different ambient odor conditions. At low odor intensities, (i.e. subthreshold for IS spiking), they participate in local, mostly intra-glomerular processing. When activated by elevated odor concentrations, however, the same neurons will fire overshooting action potentials, resulting in the spread of inhibition more globally across the antennal lobe. Modulation of the passive and active properties of LNs may, therefore, be a deciding factor in defining the multi-glomerular representations of odors in the brain.     

Transplant Antennae and Host Brain Interact to Shape Odor Perceptual Space in Male Moths

Behavioral responses to odors rely first upon their accurate detection by peripheral sensory organs followed by subsequent processing within the brain’s olfactory system and higher centers. These processes allow the animal to form a unified impression of the odor environment and recognize combinations of odorants as single entities. To investigate how interactions between peripheral and central olfactory pathways shape odor perception, we transplanted antennal imaginal discs between larval males of two species of moth Heliothis virescens and Heliothis subflexa that utilize distinct pheromone blends. During metamorphic development olfactory receptor neurons originating from transplanted discs formed connections with host brain neurons within olfactory glomeruli of the adult antennal lobe. The normal antennal receptor repertoire exhibited by males of each species reflects the differences in the pheromone blends that these species employ. Behavioral assays of adult transplant males revealed high response levels to two odor blends that were dissimilar from those that attract normal males of either species. Neurophysiological analyses of peripheral receptor neurons and central olfactory neurons revealed that these behavioral responses were a result of: 1. the specificity of H. virescens donor olfactory receptor neurons for odorants unique to the donor pheromone blend and, 2. central odor recognition by the H. subflexa host brain, which typically requires peripheral receptor input across 3 distinct odor channels in order to elicit behavioral responses.     

The mismatch repair protein MLH1 marks a subset of strongly interfering crossovers in tomato

In most eukaryotes, the prospective chromosomal positions of meiotic crossovers are marked during meiotic prophase by protein complexes called late recombination nodules (LNs). In tomato (Solanum lycopersicum), a cytological recombination map has been constructed based on LN positions. We demonstrate that the mismatch repair protein MLH1 occurs in LNs. We determined the positions of MLH1 foci along the 12 tomato chromosome pairs (bivalents) during meiotic prophase and compared the map of MLH1 focus positions with that of LN positions. On all 12 bivalents, the number of MLH1 foci was approximately 70% of the number of LNs. Bivalents with zero MLH1 foci were rare, which argues against random failure of detecting MLH1 in the LNs. We inferred that there are two types of LNs, MLH1-positive and MLH1-negative LNs, and that each bivalent gets an obligate MLH1-positive LN. The two LN types are differently distributed along the bivalents. Furthermore, cytological interference among MLH1 foci was much stronger than interference among LNs, implying that MLH1 marks the positions of a subset of strongly interfering crossovers. Based on the distances between MLH1 foci or LNs, we propose that MLH1-positive and MLH1-negative LNs stem from the same population of weakly interfering precursors.     

A single sex pheromone receptor determines chemical response specificity of sexual behavior in the silkmoth Bombyx mori

In insects and other animals, intraspecific communication between individuals of the opposite sex is mediated in part by chemical signals called sex pheromones. In most moth species, male moths rely heavily on species-specific sex pheromones emitted by female moths to identify and orient towards an appropriate mating partner among a large number of sympatric insect species. The silkmoth, Bombyx mori, utilizes the simplest possible pheromone system, in which a single pheromone component, (E, Z)-10,12-hexadecadienol (bombykol), is sufficient to elicit full sexual behavior. We have previously shown that the sex pheromone receptor BmOR1 mediates specific detection of bombykol in the antennae of male silkmoths. However, it is unclear whether the sex pheromone receptor is the minimally sufficient determination factor that triggers initiation of orientation behavior towards a potential mate. Using transgenic silkmoths expressing the sex pheromone receptor PxOR1 of the diamondback moth Plutella xylostella in BmOR1-expressing neurons, we show that the selectivity of the sex pheromone receptor determines the chemical response specificity of sexual behavior in the silkmoth. Bombykol receptor neurons expressing PxOR1 responded to its specific ligand, (Z)-11-hexadecenal (Z11-16:Ald), in a dose-dependent manner. Male moths expressing PxOR1 exhibited typical pheromone orientation behavior and copulation attempts in response to Z11-16:Ald and to females of P. xylostella. Transformation of the bombykol receptor neurons had no effect on their projections in the antennal lobe. These results indicate that activation of bombykol receptor neurons alone is sufficient to trigger full sexual behavior. Thus, a single gene defines behavioral selectivity in sex pheromone communication in the silkmoth. Our findings show that a single molecular determinant can not only function as a modulator of behavior but also as an all-or-nothing initiator of a complex species-specific behavioral sequence.     

Antennal receptive fields of pheromone-responsive projection neurons in the antennal lobes of the male sphinx moth Manduca sexta

Stimulation of the antenna of the male moth, Manduca sexta, with a key component of the female's sex pheromone and a mimic of the second key component evokes responses in projection neurons in the sexually dimorphic macroglomerular complex of the antennal lobe. Using intracellular recording and staining techniques, we studied the antennal receptive fields of 149 such projection neurons. An antennal flagellum was stimulated in six regions along its proximo-distal axis with one or both of the pheromone-related compounds while activity was recorded in projection neurons. These neurons fell mainly into two groups, based on their responses to the two-component blend: neurons with broad receptive fields that were excited when any region of the flagellum was stimulated, and neurons selectively excited by stimulation of the proximal region of the flagellum. Projection neurons that were depolarized by stimulation of one antennal region were not inhibited by stimulation of other regions, suggesting absence of antennotopic center-surround organization. In most projection neurons, the receptive field was determined by afferent input evoked by only one of the two components. Different receptive-field properties of projection neurons may be related to the roles of these neurons in sensory control of the various phases of pheromone-modulated behavior of male moths. Accepted: 30 January 1998     

Light activates output from evening neurons and inhibits output from morning neurons in the Drosophila circadian clock

Animal circadian clocks are based on multiple oscillators whose interactions allow the daily control of complex behaviors. The Drosophila brain contains a circadian clock that controls rest–activity rhythms and relies upon different groups of PERIOD (PER)–expressing neurons. Two distinct oscillators have been functionally characterized under light-dark cycles. Lateral neurons (LNs) that express the pigment-dispersing factor (PDF) drive morning activity, whereas PDF-negative LNs are required for the evening activity. In constant darkness, several lines of evidence indicate that the LN morning oscillator (LN-MO) drives the activity rhythms, whereas the LN evening oscillator (LN-EO) does not. Since mutants devoid of functional CRYPTOCHROME (CRY), as opposed to wild-type flies, are rhythmic in constant light, we analyzed transgenic flies expressing PER or CRY in the LN-MO or LN-EO. We show that, under constant light conditions and reduced CRY function, the LN evening oscillator drives robust activity rhythms, whereas the LN morning oscillator does not. Remarkably, light acts by inhibiting the LN-MO behavioral output and activating the LN-EO behavioral output. Finally, we show that PDF signaling is not required for robust activity rhythms in constant light as opposed to its requirement in constant darkness, further supporting the minor contribution of the morning cells to the behavior in the presence of light. We therefore propose that day–night cycles alternatively activate behavioral outputs of the Drosophila evening and morning lateral neurons.     

Light Activates Output from Evening Neurons and Inhibits Output from Morning Neurons in the Drosophila Circadian Clock

Animal circadian clocks are based on multiple oscillators whose interactions allow the daily control of complex behaviors. The Drosophila brain contains a circadian clock that controls rest–activity rhythms and relies upon different groups of PERIOD (PER)–expressing neurons. Two distinct oscillators have been functionally characterized under light-dark cycles. Lateral neurons (LNs) that express the pigment-dispersing factor (PDF) drive morning activity, whereas PDF-negative LNs are required for the evening activity. In constant darkness, several lines of evidence indicate that the LN morning oscillator (LN-MO) drives the activity rhythms, whereas the LN evening oscillator (LN-EO) does not. Since mutants devoid of functional CRYPTOCHROME (CRY), as opposed to wild-type flies, are rhythmic in constant light, we analyzed transgenic flies expressing PER or CRY in the LN-MO or LN-EO. We show that, under constant light conditions and reduced CRY function, the LN evening oscillator drives robust activity rhythms, whereas the LN morning oscillator does not. Remarkably, light acts by inhibiting the LN-MO behavioral output and activating the LN-EO behavioral output. Finally, we show that PDF signaling is not required for robust activity rhythms in constant light as opposed to its requirement in constant darkness, further supporting the minor contribution of the morning cells to the behavior in the presence of light. We therefore propose that day–night cycles alternatively activate behavioral outputs of the Drosophila evening and morning lateral neurons.     

Local interneuron diversity in the primary olfactory center of the moth <Emphasis Type="Italic">Manduca sexta</Emphasis>

Local interneurons (LNs) play important roles in shaping and modulating the activity of output neurons in primary olfactory centers. Here, we studied the morphological characteristics, odor responses, and neurotransmitter content of LNs in the antennal lobe (AL, the insect primary olfactory center) of the moth Manduca sexta. We found that most LNs are broadly tuned, with all LNs responding to at least one odorant. 70% of the odorants evoked a response, and 22% of the neurons responded to all the odorants tested. Some LNs showed excitatory (35%) or inhibitory (33%) responses only, while 33% of the neurons showed both excitatory and inhibitory responses, depending on the odorant. LNs that only showed inhibitory responses were the most responsive, with 78% of the odorants evoking a response. Neurons were morphologically diverse, with most LNs innervating almost all glomeruli and others innervating restricted portions of the AL. 61 and 39% of LNs were identified as GABA-immunoreactive (GABA-ir) and non-GABA-ir, respectively. We found no correlations between odor responses and GABA-ir, neither between morphology and GABA-ir. These results show that, as observed in other insects, LNs are diverse, which likely determines the complexity of the inhibitory network that regulates AL output.     

Physiology and morphology of projection neurons in the antennal lobe of the male mothManduca sexta

1. We have used intracellular recording and staining, followed by reconstruction from serial sections, to characterize the responses and structure of projection neurons (PNs) that link the antennal lobe (AL) to other regions of the brain of the male sphinx moth Manduca sexta. 2. Dendritic arborizations of the AL PNs were usually restricted either to ordinary glomeruli or to the male-specific macroglomerular complex (MGC) within the AL neuropil. Dendritic fields in the MGC appeared to belong to distinct partitions within the MGC. PNs innervating the ordinary glomeruli had arborizations in a single glomerulus (uniglomerular) or in more than one ordinary glomerulus of one AL (multiglomerular) or in one case, in single glomeruli in both ALs (bilateral-uniglomerular). One PN innervated the MGC and many or all ordinary glomeruli of the AL. 3. PNs with dendritic arborizations in the ordinary glomeruli and PNs associated with the MGC typically projected both to the calyces of the ipsilateral mushroom body and to the lateral protocerebrum, but some differences in the patterns of termination in those regions have been noted for the two classes of PNs. One PN conspicuously lacked branches in the calyces but did project to the lateral protocerebrum. The PN innervating the MGC and many ordinary glomeruli projected to the calyces of the ipsilateral mushroom body and the superior protocerebrum. 4. Crude sex-pheromone extracts excited all neurons with arborizations in the MGC, although some were inhibited by other odors. One P(MGC) was excited by crude sex-pheromone extract and by a mimic of one component of the pheromone blend but was inhibited by another component of the blend. 5. PNs with dendritic arborizations in ordinary glomeruli were excited or inhibited by certain non-pheromonal odors. Some of these PNs also responded to mechanosensory stimulation of the antennae. 6. The PN with dendritic arborizations in the MGC and many ordinary glomeruli was excited by crude sex-pheromone extracts and non-pheromonal odors and also responded to mechanosensory stimulation of the antenna.     

Different seasonal rearing conditions do not affect pheromone-sensitive receptor neurons of the adult cabbage looper moth, Trichoplusia ni

Abstract. In southern parts of the United States the cabbage looper moth, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), is multivoltine, and therefore successive generations experience different environmental conditions during development from larvae to adults.Since environmental conditions are thought to influence pheromone communication, we tested the effects of two different temperature and light regimes (selected to mimic those occurring in the spring and summer growing seasons in the south) during rearing on the response characteristics of the adult male olfactory receptor neurons responsible for detecting the major component of the female pheromone.The dose-response functions of receptor neurons from the warm- and cold-reared insects were similar in both their slopes and thresholds to stimulation with the major component of the female-emitted pheromone, (Z)-7, dodecen-1-ol acetate and (Z)-7, dodecen-1-ol, a behavioural inhibitor.In double pulse experiments, designed to emulate the temporal dispersion of pheromone in nature, neurons were stimulated with short pulses (200 ms) of (Z)-7, dodecen-1-ol acetate separated by varying intervals.Intervals as short as 30 ms reduced the response to a second pulse by over 50%.When the intervals between pulses were longer than 2 s, significant differences were not seen between the responses to the first and to the second pulse.These temporal response patterns were similar in both warm- and cold-reared animals.     

Decyl-thio-trifluoropropanone, a competitive inhibitor of moth pheromone receptors

An earlier study (Pophof 1998) showed that the esterase inhibitor decyl-thio-trifluoropropanone inhibited the responses of two receptor neurons of the moth Antheraea polyphemus tuned to straight-chain pheromone components, an acetate and an aldehyde, respectively. Here we report that decyl-thio-trifluoropropanone also inhibited the responses of two pheromone receptor neurons of Bombyx mori to bombykol and bombykal. In contrast, decyl-thio-trifluoropropanone activated receptor neurons of the moth Imbrasia cytherea tuned to the pheromone component (Z)-5-decenyl 3-methyl-butanoate. However, decyl-thio-trifluoropropanone did not affect the responses of two receptor neurons of B. mori females specialized to the plant volatiles benzoic acid and linalool, respectively. These results indicate that decyl-thio-trifluoropropanone, besides inhibiting the sensillar esterase, interferes with proteins involved specifically in the excitation of pheromone receptor neurons. In binding studies with radiolabelled decyl-thio-trifluoropropanone, the inhibitor was bound by the pheromone-binding protein of A. polyphemus. However, the amount of decyl-thio-trifluoropropanone causing response inhibition was 300 times lower than the amount of pheromone-binding protein present in the sensilla. Since the amount of decyl-thio-trifluoropropanone adsorbed corresponded to about the maximum number of receptor molecules calculated per sensillum, we expect that decyl-thio-trifluoropropanone, probably in complex with pheromone-binding protein, competitively inhibits the pheromone receptor molecules. Accepted: 8 January 2000     

Identification and Characterization of Pheromone Receptors and Interplay between Receptors and Pheromone Binding Proteins in the Diamondback Moth,Plutella xyllostella

Moths depend on olfactory cues such as sex pheromones to find and recognize mating partners. Pheromone receptors (PRs) and Pheromone binding proteins (PBPs) are thought to be associated with olfactory signal transduction of pheromonal compounds in peripheral olfactory reception. Here six candidate pheromone receptor genes in the diamondback moth, Plutella xyllostella were identified and cloned. All of the six candidate PR genes display male-biased expression, which is a typical characteristic of pheromone receptors. In the Xenopus-based functional study and in situ hybridization, PxylOR4 is defined as another pheromone receptor in addition to the previously characterized PxylOR1. In the study of interaction between PRs and PBPs, PxylPBPs could increase the sensitivity of the complex expressing oocyte cells to the ligand pheromone component while decreasing the sensitivity to pheromone analogs. We deduce that activating pheromone receptors in olfactory receptor neurons requires some role of PBPs to pheromone/PBP complex. If the chemical signal is not the pheromone component, but instead, a pheromone analog with a similar structure, the complex would have a decreased ability to activate downstream pheromone receptors.     

Responses in highly selective sensory neurons to blends of pheromone components in the moth Agrotis segetum

Pheromone detecting sensory neurons in moths are known to be highly sensitive and selective. Female-emitted sexual pheromones are normally mixtures of a few to several components. However, not much is known about how receptor neurons respond to blends of compounds. In the present study we investigated how four physiological types of pheromone component-selective neurons responded to binary mixtures or to the complete blend in the turnip moth Agrotis segetum. We found that responses to mixtures only rarely differed from that to the excitatory component alone. The mixture interactions were exclusively suppressive and occurred only at high concentrations. Therefore we conclude that the, in A. segetum, commonly observed mixture interactions observed in higher brain centra are mainly the result of central nervous processing and that information about the pheromone components reaches the antennal lobes virtually unaltered. In addition, we found a physiological type of receptor neuron, responding selectively to one of the female-emitted pheromone components, that has previously not been observed in the Swedish population.     

Identification of the sex pheromone components secreted by female moths of Peridroma saucia (Noctuidae: Noctuinae)

The variegated cutworm, Peridroma saucia Hübner, is a lepidopteran pest to a large number of crops in Canada, the United States, and Europe. It was probably naturalized in Japan in the 1970s. The pheromone glands of the female moth include two components with electroantennographic activity in a ratio of 3:1. GC-MS analyses of pheromone extracts untreated and treated with dimethyl disulfide revealed the major component to be (Z)-11-hexadecenyl acetate and the minor component to be (Z)-9-tetradecenyl acetate. The synthetic pheromone was used to attract a large number of males in a vegetable field in Tokyo, which suggests that this species has already become a harmful pest in Japan.     

Responses to sex pheromone and plant odours by olfactory receptor neurons housed in sensilla auricillica of the codling moth, Cydia pomonella (Lepidoptera: Tortricidae)

Antennal olfactory receptor neurons located in a limited number of two types of sensilla auricillica, the rabbit-eared shoehorn and the regular shoehorn, located on the 5-30 flagellomere of the codling moth, Cydia pomonella, antenna were screened for selectivity to 11 plant compounds, the major sex pheromone component, three minor pheromone components and one behavioural antagonist. Both types of sensilla housed at least three neurons characterised by different action potential amplitudes. Neurons in both males and females responded to the plant compounds, ethyl (E,Z)-2,4-decadienoate, (+/-)-linalool, (E)-ss-farnesene, hexanol, (Z)-3-hexenyl acetate, 4,8-dimethyl-1,3,(E)7-nonatriene, nonanol, the major pheromone component codlemone [(E,E)-8,10-dodecadienol] and the minor pheromone component tetradecanol. Additionally, (E,E)-alpha-farnesene and (Z)-3-hexenol elicited responses specifically in female neurons, whereas (E,E)-farnesol elicited a specific response in a male neuron. Neurons responded to 1-3 odorants, with sometimes overlapping response spectra. A scanning electron microscopic study of the antennae of both sexes supported an earlier study, apart from that long s. trichodea were present in a wreath at the proximal margin of the flagellomere and in addition evenly distributed over the remaining surface, and a previously non-described sensillum type with external basiconic features was revealed, distributed on the proximal and medial region of the flagellomeres.     

Endogenous control of circadian rhythms of pheromone production in the turnip moth, Agrotis segetum

The circadian variation of pheromone production in the turnip moth, Agrotis segetum, was characterized by quantifying (Z)-7-dodecenyl acetate (Z7-12:OAc), the most abundant pheromone component produced by female turnip moth, at different times of day. Under 17:7 h light-dark cycle (LD), the peak of Z7-12:OAc production occurred around 4 h into the scotophase, while there was very little pheromone production during the photophase. When females were maintained under constant darkness (DD), the periodicity of pheromone production was sustained for 3 consecutive days. Furthermore, the rhythm in pheromone production could be entrained to a shifted LD. These results demonstrate that the pheromone production in the turnip moth is regulated endogenously by a circadian clock. To understand how the circadian rhythm of pheromone production is generated, circadian variation of pheromone- biosynthesis-activating neuropeptide (PBAN)-like activity in the brain-suboesophageal ganglion complexes (Br-SOG), hemolymph, and ventral nerve cord (VNC) was also examined. Under both LD and DD, only the VNC displayed a circadian variation in the PBAN-like activity, which was significantly higher during the late-photophase than that in the scotophase. In addition, the present study showed that removal of VNC in isolated abdomen did not affect PBAN stimulation of pheromone production, while severing the VNC impaired normal pheromone production. The role of Br-SOG, VNC, and hemolymph in the regulation of the periodicity of pheromone production is discussed.     

How neurons may compute: The case of insect sexual pheromone discrimination

Recognition of pheromone scent by male insects probably depends on analyzing the blend's composition in terms of relative concentrations of major and minor molecular components. Based on anatomical, physiological and behavioral data concerning certain moth species and the cockroach, we propose a simple, biologically plausible neural circuit which is able to perform this task reliably. The model employs oscillations as a detecting device. This principle is easily generalized to other systems. As a computational device, ratio detection may find applications in a variety of biological situations, e.g. in the olfactory system of all animals.