Production and perception of pheromones by the beetle Tribolium confusum

Adults of Tribolium confusum secrete two pheromones. The first, produced by the male, is attractive to both sexes and the second, produced by the female, is attractive to the male only. Pheromone production and perception was studied in relation to habituation, beetle age, time of day and previous mating. A living source of each pheromone habituates the responding beetles, the male pheromone habituating more strongly; female pheromone habituates only in the absence of the male pheromone. Habituation to one pheromone was always accompanied by an enhanced response to the other.Five days after emergence, production of male pheromone reaches a peak that is maintained. Production of female pheromone peaks after 3 days. Both sexes are responsive to male pheromone immediately upon eclosion, males reaching maximum response at 14 days, females at 8 days. Males are also responsive to female pheromone upon eclosion reaching maximum response at 8 days; female response to female pheromone is imperceptible. Males but not females display a 24 hr rhythm in pheromone production. Mated beetles did not differ significantly from unmated beetles in their ability to perceive pheromones. Alteration in male pheromone production after mating was detected by females but not males; this pheromone may, therefore, act as both a sex and aggregation pheromone.     

Factors influencing response of flying Prostephanus truncatus to its male-produced aggregation pheromone

Abstract. The effects of age, sex, mating status, pre-exposure to pheromone, resource (diet) quality, and starvation on the response of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) to its male-produced aggregation pheromone were investigated.Age was an important factor determining the level of response to pheromone: young adults were more responsive than older adults.The suitability of the resource in which P.truncatus is present affected its dispersal tendency, but not its sensitivity to pheromone per se. Sex, mating status, brief prior exposure to pheromone, and starvation did not influence the response of the larger grain borer to pheromone.The orientation behaviour of the beetle is described, and it is proposed that the pheromone primarily functions as a 'suitable resource location and colonization signal'.     

Comparison of pheromone application rates, point source densities, and dispensing methods for mating disruption of tufted apple bud moth (Lepidoptera: Tortricidae)

Small-plot (approximately 0.1 ha) studies were used to evaluate different pheromone dispensing systems, application rates, and point-source densities for mating disruption of the tufted apple bud moth, Platynota idaeusalis (Walker). Using polyvinyl chloride spirals impregnated with tufted apple bud moth pheromone (1:1 ratio of E11-tetradecenyl alcohol/E11-tetradecenyl acetate), pheromone rates of > or = 1,482 spirals per hectare (74.1 g pheromone per hectare) were superior to a rate of 988 spirals per hectare (49.4 g pheromone per hectare) in decreasing male response to pheromone traps in 1995, whereas no differences were detected among rates of 988, 1,482 and 1,975 spirals per hectare in 1996. Within a range of 370-988 pheromone dispensers per hectare, point source densities were equally effective in suppressing male response to pheromone traps. Pheromone-impregnated paraffin disks were equally effective at inhibiting male response to pheromone traps compared with polyvinyl chloride spirals. However, a paraffin emulsion formulation of pheromone applied with a hand-held grease gun provided longer residual communication disruption effects than polyvinyl chloride spirals. Dilution of paraffin emulsion pheromone formulations in water for application with a backpack sprayer and airblast sprayer rendered them ineffective in reducing male response to pheromone traps. The releases of pheromone from polyvinyl chloride spirals and paraffin disks aged in the field were described by a linear and negative logarithmic curve, respectively, indicating that dispenser life time should be longer for spirals. The ratio of acetate to alcohol components of pheromone released from spirals increased over time, whereas the release ratio remained more constant for paraffin disks. This suggests that the disruption efficacy of spirals may be prematurely reduced because of imbalance of the released components.     

Population variation and genetic control of pheromone communication systems in moths

The nature of variation in moth pheromone communication systems and its genetic control is critical for the evolution of these systems and for their role in mate-finding and reproductive isolation. Significant additive genetic variance has been demonstrated in female pheromone production in monomorphic populations. However, corresponding variance in male pheromone response with respect to the blend which is most active, appears to be low, as can be expected from the general asymmetry of sexual selection. Pheromone polymorphism and differences in communication systems between closely related species seem to be controlled by a small number of Mendelian genes. The critical biosynthetic steps, which are influenced by the genes controlling pheromone production, can be inferred from our present knowledge of pheromone biosynthesis. A mechanistic understanding of how male response to pheromones is controlled is further away. Failure to demonstrate genes with pleiotropic effects on critical sender and receiver traits, suggests that reciprocal selection on genetically independent sender and receiver loci is the more likely explanation for the generally observed coordination between pheromone production and response in moth populations. Further research on the evolutionary significance of Z-linked pheromone response genes, documented in several species, should be encouraged. Investigations, in the field, of populations that vary in pheromone production and response, and theoretical and empirical studies of the survival of sender and receiver mutants in otherwise monomorphic populations are also important to advance our understanding of how pheromone communication systems evolve.     

Antipredator responses to alarm pheromone in groups of young and/or old thrips larvae

Many prey species suffer from different predators in the course of their ontogeny. Hence, the alarm signal a small prey individual sends can have a different meaning than the signal a large prey individual sends, both for small and for large receivers. Larvae of Western Flower Thrips face predators that attack only small larvae, or predators that attack small larvae and large larvae. Furthermore, thrips larvae release a two‐component alarm pheromone, which varies in composition with larval age. Here, we study whether their response to alarm pheromone varies with composition of the pheromone. First, we confirmed that large and small larvae respond when nearby larvae of both sizes were prodded with a brush to induce alarm pheromone excretion. Subsequently, we tested whether thrips larvae of a given size respond differentially to alarm pheromone excreted by a small or large companion larva. We analyzed two types of behavior used in direct defense against a predator and one type of escape response. Only small (not large) larvae attempted to escape more frequently in response to excretions from a large larva. This difference in response could have been due to the alarm pheromone or to the companion larva in the vicinity. We subsequently tested for, but did not find, an effect of size of the companion larva on the behavior of the test larva when exposed to synthetic pheromone mimicking that of a large larva. Finally, we tested how pheromone composition affects antipredator behavior by exposing thrips larvae to synthetic pheromones differing in amount and ratio of the two components. Only for small larvae, we found significant changes in escape behavior with pheromone amount, and a trend with the ratio. Overall, we conclude that small thrips larvae respond differentially to alarm pheromones excreted by small and large larvae and that this differential response is due to differences in pheromone quantity and possibly also quality. Our results suggest that responses to alarm signals can vary with the chemical composition of those alarm signals.     

Ustilago maydis Mating Hyphae Orient Their Growth toward Pheromone Sources

Snetselaar, K. M., Bolker, M., and Kahmann, R. 1996. Ustilago maydis mating hyphae orient their growth toward pheromone sources. Fungal Genetics and Biology 20, 299-312. When small drops of Ustilago maydis sporidia were placed 100-200 μm apart on agar surfaces and covered with paraffin oil, sporidia from one drop formed thin hyphae that grew in a zig-zag fashion toward the other drop if it contained sporidia making the appropriate pheromone. For example, a2b2 mating hyphae grew toward a1b1 and a1b2 mating hyphae, and the filaments eventually fused tip to tip. Time-lapse photography indicated that the mating hyphae can rapidly change orientation in response to nearby compatible sporidia. When exposed to pheromone produced by cells in an adjacent drop, haploid sporidia with the a2 allele began elongating before sporidia with the a1 allele. Sporidia without functional pheromone genes responded to pheromone although they did not induce a response, and sporidia without pheromone receptors induced formation of mating hyphae although they did not form mating hyphae. Diploid sporidia heterozygous at b but not at a formed straight, rigid, aerial filaments when exposed to pheromone produced by the appropriate haploid sporidia. Again, the a2a2b1b2 strain formed filaments more quickly than the a1a1b1b2 strain. Taken together, these results suggest that the a2 pheromone diffuses less readily or is degraded more quickly than the a1 pheromone.     

溴氰菊酯对亚洲玉米螟雄蛾感受雌性信息素的影响

为了探索溴氰菊醋对亚洲玉米螟雄蛾感受雌性信息素的影响,本文运用触角电位仪和风洞装置对亚洲玉米螟雄蛾进行了电生理和行为反应的测试．结果表明,处理雄蛾对不同比例雌性信息素的触角电位反应分别在E／Z;1／9、5／5和9／1处出现峰值,与对照相比无显著改变,但反应幅度为0．25—0．45mV,比对照下降0．15—0．35mV．对不同剂量的性信息素,引起可见触角电位反应的低限阈值为1ng,饱和反应剂量为10000ng,但反应幅度亦下降0．1—0．5mV,说明溴氰菊酯主要是影响雄蛾周缘感受系统的敏感性．但在风洞测试中,雄蛾除在反应率上比对照明显降低外,其峰值感受比例从E／Z＝1／1漂移到7／3以上．雄蛾对雌性信息素的低限反应剂量也从10ng漂移到100ng,并且高限反应剂量也从100000ng降低到50000ng,使有效作用剂量范围缩小．这说明溴氰菊酯对雄蛾的行为反应有较大影响,不仅使雄蛾对性信息素感受的敏感性降低,也影响到其感受的专化性。     

Characterization of comQ and comX, Two Genes Required for Production of ComX Pheromone in Bacillus subtilis

Many microbes use secreted peptide-signaling molecules to stimulate changes in gene expression in response to high population density, a process called quorum sensing. ComX pheromone is a modified 10-amino-acid peptide used by Bacillus subtilis to modulate changes in gene expression in response to crowding. comQ and comX are required for production of ComX pheromone. We found that accumulation of ComX pheromone in culture supernatant paralleled cell growth, indicating that there was no autoinduction of production of ComX pheromone. We overexpressed comQ and comX separately and together and found that overexpression of comX alone was sufficient to cause an increase in production of ComX pheromone and early induction of a quorum-responsive promoter. These results indicate that the extracellular concentration of ComX pheromone plays a major role in determining the timing of the quorum response and that expression of comX is limiting for production of ComX pheromone. We made alanine substitutions in the residues that comprise the peptide backbone of ComX pheromone. Analysis of these mutants highlighted the importance of the modification for ComX pheromone function and identified three residues (T50, G54, and D55) that are unlikely to interact with proteins involved in production of or response to ComX pheromone. We have also identified and mutated a putative isoprenoid binding domain of ComQ. Mutations in this domain eliminated production of ComX pheromone, consistent with the hypothesis that ComQ is involved in modifying ComX pheromone and that the modification is likely to be an isoprenoid.     

Chemosensory regulation of development in C. elegans

The dauer larva is a specialized third-larval stage of Caenorhabditis elegans that is long-lived and resistant to environmental insult. The dauer larva is formed in response to a high external concentration of a constitu-tively secreted pheromone. Response to the dauer-inducing pheromone of C. elegans is a promising genetic model for metazoan chemosensory transduction. More than 20 genes have been identified that are required for normal pheromone response. The functions of these genes include production of the pheromone, exposure of sensory neuron endings to the environment, structural and functional integrity of those sensory endings, and the capacity of sensory neurons to make appropriate output. Genetic evidence suggests that two partially redundant sensory pathways act in concert to control dauer formation. At least two classes of chemosensory neurons, ADF and ASI, are implicated in the pheromone response. On the basis of on these findings, a speculative model for the pheromone response is proposed. In this model, the neurons ADF and ASI are pheromone sensors that repress dauer formation in the absence of pheromone and dere-press dauer formation in response to pheromone. It is currently unclear whether or not the two genetically defined sensory pathways both act in ADF and ASI.     

Male orientation to trail sex pheromones in parasitoid wasps: does the spatial distribution of virgin females matter?

We studied male locomotory response to trails and patches of sex pheromone (left respectively by free-ranging females and females constrained to stay on a small area) in the two parasitoids Aphelinus asychis (Hymenoptera: Aphelinidae) and Trichogramma brassicae (Hymenoptera: Trichogrammatidae). Under the hypothesis that the spatial distribution of virgin females differs between these species (scattered among host plants in A. asychis, gregarious at emergence sites in T. brassicae), we predicted that male locomotory response to their sex pheromones should also differ: A. asychis males should follow pheromone trails on plants in order to encounter the females along these trails, whereas T. brassicae males should stay on pheromone patches, at emergence sites, and mate the females on these patches. Using an improved video-tracking system, we found that males of both species respond to conspecific sex pheromone trails and patches, but that the response does not differ much between species. Males released on marked substrates walked in a more convoluted pattern (i.e. higher path fractal dimension and higher number of crossings within tracks) than males released on unmarked substrates. On pheromone patches, males turned persistently in the same direction when leaving the patch, which explains a higher number of visits on marked patches than on unmarked patches, and possibly, higher track convolution on pheromone trails. Contrary to our hypothesis, male A. asychis did not follow female trails more accurately than male T. brassicae, and male T. brassicae did not stay longer on pheromone patches than male A. asychis. We argue that these discrepancies between our predictions and the observed responses originates from discrepancies between the assumed spatial distribution of virgin females and their actual distribution in the wild.     

The roles of juvenile hormone and biogenic amines on pheromone response plasticity and diapause termination in male Caloptilia fraxinella

In insects that exhibit a period of delayed reproduction, the timing of mating and reproduction is controlled by environmental conditions that regulate endogenous factors such as hormones and biogenic amines (BAs). Caloptilia fraxinella (Ely) (Lepidoptera: Gracillariidae) undergoes a 9‐month reproductive diapause from adult eclosion in the summer until diapause termination the following spring when adults mate. Male response to female sex pheromone is plastic, and is most acute when moths are reproductively active. The aim of this study is to further elucidate the mechanisms involved in the regulation of male response to pheromone in C. fraxinella, and to test whether the application of BAs with and without a juvenile hormone analogue (JHA) to males in different physiological states impacts pheromone responsiveness, as measured by electroantennogram and wind tunnel bioassays. Treatment of male C. fraxinella in reproductive diapause with one application of a JHA induces the highest subsequent pheromone response in the fall, but does not alter pheromone response earlier in reproductive diapause in the summer. The JHAs methoprene and pyriproxyfen similarly enhance pheromone response in the fall. Treatment with methoprene alone or in combination with one of the BAs octopamine, dopamine or serotonin increases male pheromone responsiveness in the fall. The increase in pheromone response can be attributed to methoprene only, as treatment with any of the BAs alone does not enhance male response to pheromone. Biogenic amine treatment lowers male responsiveness to pheromone in some experiments, indicating that there may be a role for BAs in maintaining low pheromone response during reproductive diapause in this species.     

Decay rates of attractive and repellent pheromones in an ant foraging trail network

Pharaoh’s ants (Monomorium pharaonis) use at least three types of foraging trail pheromone: a long-lasting attractive pheromone and two short-lived pheromones, one attractive and one repellent. We measured the decay rates of the behavioural response of ant workers at a trail bifurcation to trail substrate marked with either repellent or attractive short-lived pheromones. Our results show that the repellent pheromone effect lasts more than twice as long as the attractive pheromone effect (78 min versus 33 min). Although the effects of these two pheromones decay at approximately the same rate, the initial effect of the repellent pheromone on branch choice is almost twice that of the attractive pheromone (48% versus 25% above control). We hypothesise that the two pheromones have complementary but distinct roles, with the repellent pheromone specifically directing ants at bifurcations, while the attractive pheromone guides ants along the entire trail. Received 15 November 2007; revised 7 March 2008; accepted 18 March 2008.     

Control of Enterococcus faecalis sex pheromone cAD1 elaboration: effects of culture aeration and pAD1 plasmid-encoded determinants

Aeration of plasmid-free Enterococcus faecalis strains resulted in an 8- to 16-fold decrease in sex pheromone cAD1 activity in culture filtrates. Levels of two unrelated pheromones, cPD1 and cAM373, were unaffected by culture aeration. Aeration also resulted in a decrease in the expression of conjugative transfer functions observed in cells containing pAD1 traB mutations, verifying a link between traB function and pheromone "shutdown." Tests with a series of pAD1 mini-plasmids indicated that the product of the traB gene was involved in, but not sufficient for, pheromone shutdown; the cooperation of one or more other gene products encoded within the pheromone response control region was required.     

Multiple sex pheromones and receptors of a mushroom-producing fungus elicit mating in yeast.

The mushroom-producing fungus Schizophyllum commune has thousands of mating types defined, in part, by numerous lipopeptide pheromones and their G protein-linked receptors. Compatible combinations of pheromones and receptors encoded by different mating types regulate a pathway of sexual development leading to mushroom formation and meiosis. A complex set of pheromone-receptor interactions maximizes the likelihood of outbreeding; for example, a single pheromone can activate more than one receptor and a single receptor can be activated by more than one pheromone. The current study demonstrates that the sex pheromones and receptors of Schizophyllum, when expressed in Saccharomyces cerevisiae, can substitute for endogenous pheromone and receptor and induce the yeast pheromone response pathway through the yeast G protein. Secretion of active Schizophyllum pheromone requires some, but not all, of the biosynthetic machinery used by the yeast lipopeptide pheromone a-factor. The specificity of interaction among pheromone-receptor pairs in Schizophyllum was reproduced in yeast, thus providing a powerful system for exploring molecular aspects of pheromone-receptor interactions for a class of seven-transmembrane-domain receptors common to a wide range of organisms.     

Sucrose response thresholds of honey bee (Apis mellifera) foragers are not modulated by brood ester pheromone

Division of labor is a hallmark of eusocial insects and their ecological success can be attributed to it. Honey bee division of labor proceeds along a stereotypical ontogenetic path based on age, modulated by various internal and external stimuli. Brood pheromone is a major social pheromone of the honey bee that has been shown to affect honey bee division of labor. It elicits several physiological and behavioral responses; notably, regulating the timing of the switch from performing in-hive tasks to the initiation of foraging. Additionally, brood pheromone affects future foraging choice. In honey bees, sucrose response threshold is a physiological correlate of age of first foraging and foraging choice. Brood pheromone has been shown to modulate sucrose response threshold in young bees, but its effects on sucrose response thresholds of bees in advanced behavioral states (foragers) are not known. In this study we examined the sucrose response thresholds of two different task groups, foragers (pollen and non-pollen) and non-foraging bees, in response to honey bee brood pheromone. Sucrose response thresholds were not significantly different between brood pheromone treatment and controls among both non-pollen and pollen foragers. However, the sucrose response threshold of non-foraging bees was significantly higher in the brood pheromone treatment group than in the control group. The switch to foraging task is considered a terminal one, with honey bee lifespan being determined at least partially by risks and stress accompanying foraging. Our results indicate that foragers are physiologically resistant to brood pheromone priming of sucrose response thresholds.