Moth pheromone receptors: gene sequences, function, and evolution

The detection of female-released species-specific sex pheromones in moths is mediated by the pheromone receptors that are expressed in the sensory neurons in the olfactory sensilla of conspecific male antennae. Since the pioneering studies on the tobacco budworm Heliothis virescens and the silkworm Bombyx mori a decade ago, genes encoding pheromone receptors have been identified from a number of moth species. Pheromone receptor genes constitute a specialized olfactory receptor subfamily that shares sequence homology. In most cases the pheromone receptor genes are more abundantly expressed in male antennae, and the expression is confined to the neurons in the long sensilla trichodea, which are responsible for pheromone sensing. Both highly specific and more broadly tuned pheromone receptors have been described in various moth species. We review the advances in moth pheromone receptor studies over the past decade, including the methods used in receptor gene isolation and functional characterization, the different ligand profiles of the identified receptors, and the evolution of this multigene family

Concerted evolution of male and female display traits in the European corn borer, Ostrinia nubilalis

BACKGROUND: Sexual reproduction entails the encounter of the sexes and the multiplicity of rituals is parallel to the diversity of mating systems. Evolutionary mechanisms such as sexual selection and sexual conflict have led to the elaboration of traits to gain attention and favours from potential partners. A paradox exists about how coordinated systems can evolve and diverge when there would seem to be a stabilising selection acting. Moth display traits - pheromones - constitute an advantageous model with which to address questions about the evolution of mating systems in animals. Both males and females can possess pheromones that are involved either in close- or long-range communication. Female and male pheromones appear to have different origins and to be under different evolutionary constraints, thus they might be envisioned as independently evolving traits. We conducted laboratory experiments to explore the role of scents released during courtship by males of the European corn borer, Ostrinia nubilalis. RESULTS: Information provided by the male pheromone appears critical for female acceptance. The composition of this male pheromone varies in an age-dependent manner and females show mating preference towards older males in choice experiments. Furthermore, male signals may allow species discrimination and reinforce reproductive isolation. Finally, we found evidence for a genetic correlation between male and female signals, the evolution of which is best explained by the constraints and opportunities resulting from the sharing of gene products. CONCLUSION: In this study we used an integrative approach to characterise the male sex pheromone in a moth. Interestingly, the male chemical signal is analogous to the female signal in that structurally similar compounds are being used by both sexes. Hence, in systems where both sexes possess display traits, the pleiotropy of genes generating the traits could influence the evolutionary trajectories of sexual signals and lead to their divergence, with speciation being the ultimate result

Dofter från choklad lockar inomhusfjärilar

Mottfjärilar, såsom indiskt mjölmott (Plodia interpunctella), kvarnmott (Ephestia kuehniella) och mandelmott (Ephestia cautella) äter inte som vuxna och använder därför födodofter främst för att fi nna äggläggningsställen. Fjärilarna utgör ett stort problem inom livsmedelsindustrin eftersom deras larver äter och förstör produkterna. Födodofterna skulle kunna användas i fällor för att locka till sig befruktade fjärilar, vilket leder till färre larver i produkterna och mindre skada. Det borde också vara möjligt att övervaka skadedjurspopulationer med hjälp av dofterna för att kunna ta beslut om när bekämpningsåtgärder ska sättas in. Olika chokladprodukter var attraktiva för både hanar och honor hos såväl indiskt mjölmott som mandelmott. En hög andel av fjärilarna flög an mot och landade på Petriskålar med krossad choklad. Jag har identifierat dofter i choklad som är attraktiva för fjärilarna. Kemikalierna utlöser både nervimpulser i antennen och olika slags beteenden. Både mandelmottet och det indiska mjölmottet flyger mot och landar på doftkällan i vindtunnelexperiment, i synnerhet när de identifierade kemikalierna presenteras i en blandning. Beteendet indikerar att identifieringen stämmer och att jag funnit åtminstone en del av de kemikalier som styr fjärilarnas attraktion till choklad. De identifierade dofterna borde därför kunna fungera som lockbete i fällor i livsmedelsindustrin. Chokladprodukterna och de syntetiska kemikalierna har testats som lockbete i flera miljöer som är drabbade av fjärilsangrepp, till exempel i en kvarn och i en djurfoderaffär. Framgången med de olika lockbetena har varit måttlig. Troligen beror de låga fällfångsterna på att fjärilarnas attraktion störs ut av omgivande dofter. I försök i ventilerade tält, där omgivande dofter saknas fångade fällor betade med chokladkemikalier kvarnmottshanar. Resultaten pekar på att omgivande dofter har negativ inverkan på fällfångster men också att framtida experiment behövs för att formge fällor som fångar honor. Där choklad misslyckas är vatten framgångsrikt. Fällor med vatten fångar både hanar och honor av mandelmottet i en chokladfabrik. Det kan definitivt användas för övervakning av mandelmottspopulationer och troligen också för direkt bekämpning. Experiment över flera månader visar en tydlig nedgång i populationstätheten i de drabbade lokalerna. En av de mest väsentliga fördelarna med vatten som lockbete är en låg kostnad för användarna, men fångsten av honor är också mycket betydelsefull. Fångsten av en befruktad hona kan betyda 200–300 färre larver i kommande generation vilket innebär avsevärt mindre skada på produkterna. I jämförelse med feromonbaserade metoder är vattenfällor därför mycket mer användbara för minskad skadegörelse

Foraging and mate-finding in the silver Y moth, Autographa gamma (Lepidoptera : Noctuidae) under the risk of predation

Animal foraging and reproductive behaviour is influenced by other simultaneous demands such as predator avoidance. The trade-offs between these demands may depend on sex or mating experience. This study demonstrates that the olfactory-mediated foraging and mate-seeking behaviours in the silver Y moths, Autographa gamma, are affected by auditory cues mimicking their bat predators. Both males and females changed their foraging behaviour under simulated predation risk. Fewer moths reached the odour source following sound stimulation and the time to find the odour source increased by up to 250%. However. there were no significant differences between male and female ability to reach the plant odour source or the duration of the flight towards the source when stimulated with ultrasound. Hence females are not more cautious than males when observed in the same behavioural context. Risk-taking in males was independent of whether they were flying toward a flower odour or sex pheromones having equal attractive value. This indicates that the trade-off between olfactory and acoustic cues is independent the type of odour. Mated females were not as strongly affected by sound as non-mated, indicating that flower odours have a higher adaptive value for mated females, suggesting that some processes following mating experience influence the trade-off between flower odours and simulated bat sounds

Disruption of the odour-mediated mating behaviour of Plodia interpunctella using high-frequency sound

Indian meal moths, Plodia interpunctella Hubner ( Lepidoptera: Pyralidae), have ears which are sensitive to high-frequency calls produced by echolocating, insectivorous bats. The influence of artificially generated, high-intensity, ultrasound signals (25 kHz, 106 dB SPL at 1 m distance) on different parameters involved in the odour-mediated mating behaviour of this species and its potential use in population control was investigated. All moths flying towards olfactory cues in flight tunnel experiments reacted strongly to a 1 s ultrasound pulse by cessation of flight and falling out of the odour plume. The source contact proportion of both male moths orienting towards the female-produced sex pheromone and of mated female moths orienting towards an oviposition cue was reduced by 40%, compared to unexposed moths. Calling females responded to the sound by retraction of the ovipositor or by falling to the ground. Long-term exposure to repetitive pulses of ultrasound suppressed female calling by up to 27%. Furthermore, mating in plastic tents was disrupted by up to 58% in ultrasound-treated tents using different sound regimens, compared to control tents. The results are discussed in relation to the potential use of ultrasound technology for the population control of pyralid stored product pests

Insect olfaction and the evolution of receptor tuning

Insects detect odorants primarily using odorant receptors (OR) housed in the dendritic membrane of olfactory sensory neurons (OSN). Pioneering studies indicated that insects, like mammals, detect odorants in a combinatorial fashion with a specific odor ligand activating several broadly tuned ORs, and each OR being activated by several ligands. Several recent studies, however, challenge this view by providing examples where ecologically relevant odorants are detected by high-specificity ORs activating dedicated neuronal circuits. Here we review these contrasting findings on the ligand selectivity of insect ORs and their neuronal wiring, and outline scenarios describing how adaptive and neutral evolution might shape both narrow and broad receptor tuning. The fact that not all ORs display narrow tuning might partly be due to key ligands having been missed from screens or too high stimuli concentrations being used. However, the birth-and-death model of OR evolution, involving both adaptive and neutral events, could also explain the evolution of broad tuning in certain receptors due to positive selection or relaxed constraint. If the insect olfactory system indeed contains both narrowly and broadly tuned ORs, this suggests that it is a hybrid between dedicated channels and combinatorial coding. The relative extent of the two coding modes is then likely to differ between species, depending on requirements of perceived chemical space and the size of the OR repertoire. We address this by outlining scenarios where certain insect groups may be more likely to have evolved combinatorial coding as their dominant coding strategy. Combinatorial coding may have evolved predominantly in insects that benefit from the ability to discriminate between a larger number of odorants and odor objects, such as polyphagous or social species. Alternatively, combinatorial coding may have evolved simply as a mechanism to increase perceived odor space in species with small OR repertoires

Sex pheromone biosynthetic pathways are conserved between moths and the butterfly Bicyclus anynana

Although phylogenetically nested within the moths, butterflies have diverged extensively in a number of life history traits. Whereas moths rely greatly on chemical signals, visual advertisement is the hallmark of mate finding in butterflies. In the context of courtship, however, male chemical signals are widespread in both groups although they likely have multiple evolutionary origins. Here, we report that in males of the butterfly Bicyclus anynana, courtship scents are produced de novo via biosynthetic pathways shared with females of many moth species. We show that two of the pheromone components that play a major role in mate choice, namely the (Z)-9-tetradecenol and hexadecanal, are produced through the activity of a fatty acyl Δ11-desaturase and two specialized alcohol-forming fatty acyl reductases. Our study provides the first evidence of conservation and sharing of ancestral genetic modules for the production of FA-derived pheromones over a long evolutionary timeframe thereby reconciling mate communication in moths and butterflies

Key biosynthetic gene subfamily recruited for pheromone production prior to the extensive radiation of Lepidoptera

<p>Abstract</p> <p>Background</p> <p>Moths have evolved highly successful mating systems, relying on species-specific mixtures of sex pheromone components for long-distance mate communication. Acyl-CoA desaturases are key enzymes in the biosynthesis of these compounds and to a large extent they account for the great diversity of pheromone structures in Lepidoptera. A novel desaturase gene subfamily that displays Δ11 catalytic activities has been highlighted to account for most of the unique pheromone signatures of the taxonomically advanced ditrysian species. To assess the mechanisms driving pheromone evolution, information is needed about the signalling machinery of primitive moths. The currant shoot borer, <it>Lampronia capitella</it>, is the sole reported primitive non-ditrysian moth known to use unsaturated fatty-acid derivatives as sex-pheromone. By combining biochemical and molecular approaches we elucidated the biosynthesis paths of its main pheromone component, the (<it>Z,Z</it>)-9,11-tetradecadien-1-ol and bring new insights into the time point of the recruitment of the key Δ11-desaturase gene subfamily in moth pheromone biosynthesis.</p> <p>Results</p> <p>The reconstructed evolutionary tree of desaturases evidenced two ditrysian-specific lineages (the Δ11 and Δ9 (18C>16C)) to have orthologs in the primitive moth <it>L. capitella </it>despite being absent in Diptera and other insect genomes. Four acyl-CoA desaturase cDNAs were isolated from the pheromone gland, three of which are related to Δ9-desaturases whereas the fourth cDNA clusters with Δ11-desaturases. We demonstrated that this transcript (<it>Lca</it>-KPVQ) exclusively accounts for both steps of desaturation involved in pheromone biosynthesis. This enzyme possesses a Z11-desaturase activity that allows transforming the palmitate precursor (C16:0) into (<it>Z</it>)-11-hexadecenoic acid and the (<it>Z</it>)-9-tetradecenoic acid into the conjugated intermediate (<it>Z,Z</it>)-9,11-tetradecadienoic acid.</p> <p>Conclusion</p> <p>The involvement of a single Z11-desaturase in pheromone biosynthesis of a non-ditrysian moth species, supports that the duplication event leading to the origin of the Lepidoptera-specific Δ11-desaturase gene subfamily took place before radiation of ditrysian moths and their divergence from other heteroneuran lineages. Our findings uncover that this novel class of enzymes affords complex combinations of unique unsaturated fatty acyl-moieties of variable chain-lengths, regio- and stereo-specificities since early in moth history and contributes a notable innovation in the early evolution of moth-pheromones.</p

Identification and Biosynthesis of Novel Male Specific Esters in the Wings of the Tropical Butterfly, Bicyclus martius sanaos

Representatives of the highly speciose tropical butterfly genus Bicyclus (Lepidoptera: Nymphalidae) are characterized by morphological differences in the male androconia, a set of scales and hair pencils located on the surface of the wings. These androconia are assumed to be associated with the release of courtship pheromones. In the present study, we report the identification and biosynthetic pathways of several novel esters from the wings of male B. martius sanaos. We found that the volatile compounds in this male butterfly were similar to female-produced moth sex pheromones. Components associated with the male wing androconial areas were identified as ethyl, isobutyl and 2-phenylethyl hexadecanoates and (11Z)-11-hexadecenoates, among which the latter are novel natural products. By topical application of deuterium-labelled fatty acid and amino acid precursors, we found these pheromone candidates to be produced in patches located on the forewings of the males. Deuterium labels from hexadecanoic acid were incorporated into (11Z)-11-hexadecenoic acid, providing experimental evidence of a Δ11-desaturase being active in butterflies. This unusual desaturase was found previously to be involved in the biosynthesis of female-produced sex pheromones of moths. In the male butterflies, both hexadecanoic acid and (11Z)-11-hexadecenoic acid were then enzymatically esterified to form the ethyl, isobutyl and 2-phenylethyl esters, incorporating ethanol, isobutanol, and 2-phenylethanol, derived from the corresponding amino acids L-alanine, L-valine, and L-phenylalanine

Identification of (E)- and (Z)-11-tetradecenyl acetate as sex pheromone components of the currant pest Euhyponomeutoides albithoracellus

The currant bud moth Euhyponomeutoides albithoracellus is a destructive pest in black currant orchards in Northern Sweden and Finland. The larvae feed on the buds, and at high densities, the species can cause severe yield losses. Sex pheromone components of the bud moth were identified via solvent extraction of excised female pheromone glands, analyses by gas chromatography with electroantennographic detection and gas chromatography–mass spectrometry and field trapping experiments. Antennae of males responded strongly and consistently to two compounds in extracts, identified as (E)-11-tetradecenyl acetate and (Z)-11-tetradecenyl acetate. Weaker and less consistent responses were observed to the corresponding alcohols, (E)-11-tetradecenol and (Z)-11-tetradecenol, and tetradecyl acetate. Field tests showed strong attraction of bud moth males to a 1:1 blend of (E)-11-tetradecenyl acetate and (Z)-11-tetradecenyl acetate. Adding the alcohols to the binary acetate blend reduced trap catches drastically, whereas tetradecyl acetate had no statistically significant impact on male attraction when added to that binary blend. Finally, testing different compositions of the binary acetate blend revealed highest catch in traps baited with a 25:75 or 50:50 ratio of the E:Z acetate isomers. The identification of sex pheromone components of the bud moth contributes to developing sustainable control of this pest via monitoring and mating disruption with sex pheromone