Antennal lobe projection destinations of Helicoverpa zea male olfactory receptor neurons responsive to heliothine sex pheromone components

We used single sensillum recordings to define male Helicoverpa zea olfactory receptor neuron physiology followed by cobalt staining to trace the axons to destination glomeruli of the antennal lobe. Receptor neurons in type A sensilla that respond to the major pheromone component, (Z)-11-hexadecenal, projected axons to the cumulus of the macroglomerular complex (MGC). In approximately 40% of these sensilla a second receptor neuron was stained that projected consistently to a specific glomerulus residing in a previously unrecognized glomerular complex with six other glomeruli stationed immediately posterior to the MGC. Cobalt staining corroborated by calcium imaging showed that receptor neurons in type C sensilla sensitive to (Z)-9-hexadecenal projected to the dorsomedial posterior glomerulus of the MGC, whereas the co-compartmentalized antagonist-sensitive neurons projected to the dorsomedial anterior glomerulus. We also discovered that the olfactory receptor neurons in type B sensilla exhibit the same axonal projections as those in type C sensilla. Thus, it seems that type B sensilla are anatomically type C with regard to the projection destinations of the two receptor neurons, but physiologically one of the receptor neurons is now unresponsive to everything except (Z)-9-tetradecenal, and the other responds to none of the pheromone-related odorants tested.     

A comparison of responses from olfactory receptor neurons of<Emphasis Type="Italic"> Heliothis subflexa</Emphasis> and<Emphasis Type="Italic"> Heliothis virescens</Emphasis> to components of their sex pheromone

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons in sensilla trichodea on male antennae of the heliothine species Heliothis subflexa and the closely related congener H. virescens. A large percentage of sensilla (72% and 81%, respectively, of all sensilla sampled) contained a single odor-responsive receptor neuron tuned to the major pheromone component of both species, Z-11-hexadecenal. A second population of sensilla on H. subflexa antennae (18%) housed receptor neurons that were tuned to Z-9-hexadecenal but also responded with less sensitivity to Z-9-tetradecenal. A similar population of sensilla (4%) on H. virescens male antennae housed receptor neurons that were shown to be tuned specifically only to Z-9-tetradecenal, with no response to even high dosages of Z-9-hexadecenal. A third population of sensilla (comprising 8% and 16% of the sensilla sampled in H. subflexa and H. virescens, respectively) housed two olfactory receptor neurons, one of which was tuned to Z-11-hexadecenyl acetate and the other tuned to Z-11-hexadecenol. In H. subflexa the Z-11-hexadecenyl acetate-tuned neuron also responded to Z-9-tetradecenal with nearly equivalent sensitivity. The behavioral requirements of males of these two species for distinct pheromonal blends was, therefore, reflected by the subtle differences in the tuning properties of antennal olfactory receptor neurons.Abbreviations MGC macroglomerular complex - ORN olfactory receptor neuron - Z9–14:Ald (Z)-9-tetradecenal - Z9–16:Ald (Z)-9-hexadecenal - Z11–16:Ac (Z)-11-hexadecenyl acetate - Z11–16:Ald (Z)-11-hexadecenal - Z11–16:OH (Z)-11-hexadecenol     

Neurons discovered in male Helicoverpa zea antennae that correlate with pheromone-mediated attraction and interspecific antagonism

Responses of single receptor neurons in the antennae of male Helicoverpa zea to sex pheromone components and to behavioral antagonists were recorded using a cut-sensillum extracellular recording technique. Three types of sensilla were identified from sampling 325 male-specific sensilla trichodea located at the lateral edge of antennomeres. The majority of these sensilla (71%) contained a receptor neuron tuned to the principal sex pheromone component (Z)-11-hexadecenal. A second sensillar type (10%) contained a receptor neuron that responded only to (Z)-9-tetradecenal. A third sensillar type (19%) contained a large-spiking neuron tuned to the secondary pheromone component (Z)-9-hexadecenal, but this neuron also could be stimulated to equivalent spike frequencies by the same emitted amounts of (Z)-9-tetradecenal. A smaller-spiking neuron in this sensillar type responded to two compounds known to act only as behavioral antagonists, (Z)-11-hexadecen-1-ol and (Z)-11-hexadecenyl acetate, and to (Z)-9-tetradecenal. Cross-adaptation studies confirmed the presence of one large- and one small-spiking neuron in the third sensillar type. Dose-response studies correlated to collected stimuli amounts showed that the large-spiking neuron in the third sensillar type was equally tuned to (Z)-9-hexadecenal and (Z)-9-tetradecenal, whereas the smaller-spiking neuron was far more sensitive to (Z)-11-hexadecen-1-ol and to (Z)-11-hexadecenyl acetate than to (Z)-9-tetradecenal. Accepted: 29 September 1997     

Glomerular targets of Heliothis subflexa male olfactory receptor neurons housed within long trichoid sensilla

We used single-sensillum recordings to characterize male Heliothis subflexa antennal olfactory receptor neuron physiology in response to compounds related to their sex pheromone. The recordings were then followed by cobalt staining in order to trace the neurons' axons to their glomerular destinations in the antennal lobe. Receptor neurons responding to the major pheromone component, (Z)-11-hexadecenal, in the first type of sensillum, type-A, projected axons to the cumulus of the macroglomerular complex (MGC). In approximately 40% of the type-A sensilla, a colocalized receptor neuron was stained that projected consistently to the posterior complex 1 (PCx1), a specific glomerulus in an 8-glomerulus complex that we call the Posterior Complex (PCx). We found that receptor neurons residing in type-B sensilla and responding to a secondary pheromone component, (Z)-9-hexadecenal, send their axons to the dorsal medial glomerulus of the MGC. As in the type-A sensilla, we found a cocompartmentalized neuron within type-B sensilla that sends its axon to a different glomerulus of the PCx4. One neuron in type-C sensilla tuned to a third pheromone component, (Z)-11-hexadecenol, and a colocalized neuron responding to (Z)-11-hexadecenyl acetate projected their axons to the anteromedial and ventromedial glomeruli of the MGC, respectively.     

Peripheral Coding of Sex Pheromone Blends with Reverse Ratios in Two Helicoverpa Species

The relative proportions of components in a pheromone blend play a major role in sexual recognition in moths. Two sympatric species, Helicoverpa armigera and Helicoverpa assulta, use (Z)-11-hexadecenal (Z11–16: Ald) and (Z)-9-hexadecenal (Z9–16: Ald) as essential sex pheromone components but in very different ratios, 97∶3 and 7∶93 respectively. Using wind tunnel tests, single sensillum recording and in vivo calcium imaging, we comparatively studied behavioral responses and physiological activities at the level of antennal sensilla and antennal lobe (AL) in males of the two species to blends of the two pheromone components in different ratios (100∶0, 97∶3, 50∶50, 7∶93, 0∶100). Z11–16: Ald and Z9–16: Ald were recognized by two populations of olfactory sensory neurons (OSNs) in different trichoid sensilla on antennae of both species. The ratios of OSNs responding to Z11–16:Ald and Z9–16:Ald OSNs were 100∶28.9 and 21.9∶100 in H. armigera and H. assulta, respectively. The Z11–16:Ald OSNs in H. armigera exhibited higher sensitivity and efficacy than those in H. assulta, while the Z9–16:Ald OSNs in H. armigera had the same sensitivity but lower efficacy than those in H. assulta. At the dosage of 10 µg, Z11–16: Ald and Z9–16: Ald evoked calcium activity in 8.5% and 3.0% of the AL surface in H. armigera, while 5.4% and 8.6% of AL in H. assulta, respectively. The calcium activities in the AL reflected the peripheral input signals of the binary pheromone mixtures and correlated with the behavioral output. These results demonstrate that the binary pheromone blends were precisely coded by the firing frequency of individual OSNs tuned to Z11–16: Ald or Z9–16: Ald, as well as their population sizes. Such information was then accurately reported to ALs of H. armigera and H. assulta, eventually producing different behaviors.     

Chemical communication in heliothine moths

The chemical and temporal features of the sex-pheromone emitted by Heliothis virescens females are encoded by a diverse array of output pathways from the male-specific macroglomerular complex (MGC) in the antennal lobe. Most output neurons (29 out of 32) were activated by antennal stimulation with the principal component of the sex-pheromone blend of this species, (Z)-11-hexadecenal. Six neurons were excited solely by this component, 8 neurons also responded to the second essential blend component, (Z)-9-tetradecenal, and 14 neurons displayed equivalent responses to the two. Many neurons also effectively encoded the onset and duration of the stimulus. In one additional neuron, a prolonged excitatory response (synergism) was evoked only by the blend of the two components, indicating that some MGC neurons function as blend detectors.In contrast to the situation in Helicoverpa zea, none of the MGC neurons in H. virescens responded selectively to (Z)-9-tetradecenal, suggesting that these two noctuid species employ different neural strategies to encode information about their respective pheromone blends.Three MGC-output neurons responded selectively to (Z)-11-hexadecenyl acetate, an odorant released by some sympatric species that disrupts normal upwind flight to pheromones. Thus, changes in the attractant and deterrent chemical signals, as well as the physical features of these odor plumes, are encoded in the MGC across a diverse parallel array of output pathways to the protocerebrum.Abbreviations AL antennal lobe - AN antennal nerve - 16:AL hexadecanal - MGC macroglomerular complex - 14:AL tetradecanal - Z11-16:AL (Z) 11-hexadecenal - Z11-16:AC (Z) 11-hexadecenyl acetate - Z9-14:AL (Z) 9-tetradecenal - Z9-14:FO (Z) 9-tetradecenyl formate     

棉铃虫雄蛾触角的毛形感器对其性信息素组分及类似物的反应

本文用单细胞电反应的记录方法,测定了棉铃虫Heliothis armigera Hubner雄蛾触角的毛形感器对其性信息素组分及雌蛾腹部提取物的反应,发现顺-11-十六碳烯醛和顺-9-十六碳烯醛能引起反应。对前者发放大脉冲,对后者发放小脉冲,对雌蛾腹部提取物发放大、小两种脉冲,但以大脉冲为主。     

Behavioral and electrophysiological responses of Helicoverpa assulta, H. armigera (Lepidoptera: Noctuidae), their F1 hybrids and backcross progenies to sex pheromone component blends

Two sibling species, Helicoverpa assulta and Helicoverpa armigera both use (Z)-9-hexadecenal and (Z)-11-hexadecenal as their sex pheromone components but in almost reversed ratios, 93:7 and 3:97, respectively. H. assulta and H. armigera males performed upwind flight in response to the H. assulta sex pheromone blend (93:7). H. armigera responded strongly to the H. armigera blend (3:97), whereas H. assulta males remained inactive upon exposure to this blend. Both species gave clear dose-dependent electrophysiological responses to (Z)-11-hexadecenal. However, (Z)-9-hexadecenal evoked strong dose-dependent electrophysiological responses in H. assulta males but not in H. armigera. The two male F₁ hybrids exhibited similar behavioral responses to two sex pheromone blends and electrophysiological responses to two pheromone components as H. armigera males. This indicated that H. armigera genes appear dominant in determining the behavioral response and electrophysiological responses. Behavioral and electrophysiological responses of backcrosses of male F₁ hybrids (H. armigera female × H. assulta male) with female H. assulta and H. armigera were close to that of H. assulta and H. armigera, respectively. However, backcrosses of female F₁ hybrids (H. assulta female × H. armigera male) with male H. assulta and H. armigera showed reduced behavioral responses but normal electrophysiological responses compared to males of the respective parental line.     

旋花蛾性信息素成分的鉴定

提取和鉴定了杂草田旋花Convolvulus arvensis的天敌旋花蛾Tyta luctuosa的性信息素主要成分,并应用风洞实验对雄蛾进行了测试。结果表明,腺体提取物和雌蛾求偶时所释放的主要性信息素成分均为2种化合物：顺-9-十四碳烯醛（Z9-14∶Ald）和顺-11-十六碳烯醛（Z11-16∶Ald）。腺体提取物中2种化合物的总量在个体间差异很大（22～167 ng）,但二者的比率相对稳定（Z9-14∶Ald/Z11-16∶Ald=0.3±0.15）。雌蛾所释放的性信息素量及比率在个体间也存在差异。每只雌蛾求偶时平均每小时释放94 ng Z9-14∶Ald和45 ng Z11-16∶Ald,平均比率为2.2。风洞实验结果显示,48%的雄蛾可被合成的性信息素混合物（0.4 μg Z9-14∶Ald, 2 μg Z11-16∶Ald）引诱完成逆风飞行并最终触及刺激源,而2种对照组（以求偶期雌蛾或性信息素腺体提取物为刺激源）的引诱率则分别为62%和44%。     

(Z)-9-tetradecenal: a potent inhibitor of pheromone-mediated communication in the oriental tobacco budworm moth,Helicoverpa assulta

The behavioural significance of (Z)-9-tetradecenal to male H. assulta was tested by comparing the number of moths attracted to lures containing a standard synthetic female sex pheromone with lures in which (Z)-9-tetradecenal was also added. The standard pheromone mixture used contained 1000 g (Z)-9-hexadecenal, 50 g (Z)-11-hexadecenal, 300 g (Z)-9-hexadecenyl acetate and 15 g (Z)-11-hexadecenyl acetate impregnated on rubber septa. Addition of (Z)-9-tetradecenal to the standard pheromone was shown to significantly reduce the caught of male H. assulta when added in amounts greater than 10 g or 1% of the major pheromone component in both field and net-house experiments. The reduction in catch was found to be dependent on the quantity of (Z)-9-tetradecenal added to the standard pheromone. The implications of these results on conspecific and inter-specific pheromone-mediated communication in H. assulta and related sympatric heliothine species is discussed.Abbreviations Z9-16:AL (Z)-9-hexadecenal - Z11-16:AL (Z)-11-hexadecenal - Z9-16:AC (Z)-9-hexadecenyl acetate - Z11-16:AC (Z)-11-hexadecenyl acetate - Z9-14:AL (Z)-9-tetradecenal - Z9-16:OH (Z)-9-hexadecen-1-ol - Z11-16:OH (Z)-11-hexadecen-1-ol - RH relative humidity     

The significance of major pheromone components and interspecific signals as expressed by receptor neurons in the oriental tobacco budworm moth,Helicoverpa assulta

Receptor neuron specificities for intra- and interspecific chemical signals were determined in males of Helicoverpa assulta, by testing single neurons for twelve heliothine produced compounds and two chemical analogues. Three types of receptor neurons were identified in the male specific sensilla trichodea type 1.

1. One large group of neurons (29 out of 63) was tuned to the major pheromone component (Z)-9-hexadecenal, in contrast to results obtained previously in a related species, where the information from this compound seems to be mediated via neurons tuned to (Z)-9-tetradecenal.
2. Another group of neurons (28/63) was tuned to (Z)-9-tetradecenal which is not produced by the conspecific females. These neurons and those tuned to the major pheromone component, always appearing together, are probably located in the same sensillum. Their large number suggests that (Z)-9-tetradecenal mediates an important message in this species, probably causing interspecific interruption.
3. The third group of neurons (6/63) was tuned to the second principal pheromone component (Z)-11-hexadecenal. These neurons showed similar specificities as the corresponding type of neurons in related species, indicating a conservation of their membrane receptors through evolution. In contrast, the (Z)-9-tetradecenal receptor neurons in H. assulta showed a different specificity than their counterparts in the related species, suggesting that their receptor proteins have evolved differently.

     

Physiology and glomerular projections of olfactory receptor neurons on the antenna of female Heliothis virescens (Lepidoptera: Noctuidae) responsive to behaviorally relevant odors

The neurophysiology and antennal lobe projections of olfactory receptor neurons housed within short trichoid sensilla of female Heliothis virescens F. (Noctuidae: Lepidoptera) were investigated using a combination of cut-sensillum recording and cobalt-lysine staining techniques. Behaviorally relevant odorants, including intra- and inter-sexual pheromonal compounds, plant and floral volatiles were selected for testing sensillar responses. A total of 184 sensilla were categorized into 25 possible sensillar types based on odor responses and sensitivity. Sensilla exhibited both narrow (responding to few odors) and broad (responding to many odors) response spectra. Sixty-six percent of the sensilla identified were stimulated by conspecific odors; in particular, major components of the male H. virescens hairpencil pheromone (hexadecanyl acetate and octadecanyl acetate) and a minor component of the female sex pheromone, (Z)-9-tetradecenal. Following characterization of the responses, olfactory receptor neurons within individual sensilla were stained with cobalt lysine (N=39) and traced to individual glomeruli in the antennal lobe. Olfactory receptor neurons with specific responses to (Z)-9-tetradecenal, a female H. virescens sex pheromone component, projected to the female-specific central large female glomerulus (cLFG) and other glomeruli. Terminal arborizations from sensillar types containing olfactory receptor neurons sensitive to male hairpencil components and plant volatiles were also localized to distinct glomerular locations. This information provides insight into the representation of behaviorally relevant odorants in the female moth olfactory system. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Antennal olfactory sensory neurones responsive to host and nonhost plant volatiles in gorse pod moth Cydia succedana

We investigate the response profiles of the antennal olfactory sensory neurones (OSNs) in male and female gorse pod moth Cydia succedana to host and nonhost volatiles, using the single sensillum recording technique. Eight different classes of olfactory sensilla are identified in female C. succedana and five different classes of olfactory sensilla in males. Nineteen different classes of OSNs are identified from the sensilla in females, and nine different classes of OSNs in the male sensilla. All classes of sensilla, except class F7 and class M1 sensilla, co‐compartmentalize two or three OSNs in each sensillum, and the OSNs present in the same sensillum are specialized for different volatiles. Most plant‐volatile OSNs exhibit phasic‐tonic type of temporal responses, whereas the pheromone OSNs in male C. succedana show rather phasic responses. The majority of OSNs identified in C. succedana display highly specialized responses to a narrow range of volatiles, whereas only a small proportion of OSNs show broad response spectra. Two most abundant classes of OSNs exhibit highly specialized responses to β‐myrcene and (E)‐β‐ocimene, two major volatiles released by gorse (Ulex europaeus), the main host of C. succedana. By contrast, several other classes of OSNs exhibit highly specialized responses to geraniol, (Z)‐3‐hexen‐1‐ol, (±)‐α‐terpineol, citral and benzyl acetate, which are produced by various nonhost plants. Taking the results of the present study together, we suggest that C. succedana use the combinational input from a set of highly specialized OSNs for host plant volatiles and another set of highly specialized OSNs for nonhost volatiles to discriminate between hosts and nonhosts.     

Odorant response of individual sensilla on theDrosophila antenna

We have documented odor responses of all morphological classes of sensilla on the surface of theDrosophila antenna: sensilla basiconica, sensilla trichodea, and sensilla coeloconica. Both subtypes of s. basiconica, large and small, respond to odors. S. trichodea fall into different functional types. Type 1 appears narrowly tuned, as it responded only tocis-vaccenyl acetate, believed to be a pheromone. Type 2 responded totrans-2-hexenal and 4-methyl cyclohexanol. These two types of s. trichodea are differentially distributed on the antennal surface, and have dramatically different frequencies of spontaneous action potentials. Likewise, there are multiple types of s. coeloconica. One type is broadly tuned, responding most strongly to a test stimulus of butyric acid, but also to a variety of other odors; it is restricted to the dorso-medial portion of the third antennal segment. A second type gave detectable responses only totrans-2-hexenal. These results demonstrate that all classes of sensilla are olfactory, and they reveal the organizational complexity of theDrosophila olfactory system.     

An overlooked component: (Z)-9-tetradecenal as a sex pheromone in Helicoverpa armigera

The sex pheromone blend of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a multi-component system, as is that of many other moths, and (Z)-11-hexadecenal 90-99%+(Z)-9-hexadecenal 10-1% was recommended as a standard blend for attracting the species. However, this fails to account for the significance of other compounds that exist in the sex gland. The aim of the present study was to investigate the function of other compounds present in the female sex gland of H. armigera. Extract of female sex glands were analysed by GC-MS combined with GC-EAD. Total 10 compounds were identified, which two novel were reported in female sex gland: heptanal and nonanal, and some previously identified compounds were confirmed. We developed bioassays to evaluate the potential roles of these 10 compounds. In Y-tube bioassays, the gland constituents hexadecanal, (Z)-7-hexadecenal and (Z)-9-tetradecenal increased male attractiveness when added as a three-compound admixture to the standard blend. Field trapping tests showed that (Z)-9-tetradecenal doubled trap catch in comparison with the standard blend, but that the addition of (Z)-7-hexadecenal and hexadecanal did not significantly increase trap catch. These results indicated that while (Z)-7-hexadecenal and hexadecanal function well only at short range, (Z)-9-tetradecenal plays a very important role at both short and long ranges. We suggest that that (Z)-9-tetradecenal as a previously overlooked sex pheromone component of H. armigera, it should be added to sex pheromone lure formulations to improve pheromone trap sensitivity and the efficacy of commercial mating disruption.     

Comparison of male antennal morphology and sensilla physiology for sex pheromone olfactory sensing between sibling moth species: Ectropis grisescens and Ectropis obliqua (Geometridae)

Ectropis grisescens and Ectropis obliqua (Lepidoptera: Geometridae) are sibling pest species that co‐occur on tea plants. The sex pheromone components of both species contain (Z,Z,Z)‐3,6,9‐octadecatriene and (Z,Z)‐3,9‐cis‐6,7‐epoxy‐octadecadiene. E. obliqua has (Z,Z)‐3,9‐cis‐6,7‐epoxy‐nonadecadiene as an additional sex pheromone component, which ensures reproductive segregation between the two species. To ascertain the detection mechanism of olfactory organs for sex pheromone components of E. grisescens and E. obliqua, we applied scanning electron microscopy and single sensillum recording to compare antennal morphology and sensillum physiology in the two species. There was no apparent morphological difference between the antennae of the two species. Both species responded similarly to all three sex pheromone components, including, E. obliqua specific component. The distribution patterns of antennal sensilla trichodea differed between the two species. Sex pheromone olfactory sensing in these sibling species appears to be determined by the density of different types of olfactory sensing neurons. Dose‐dependent responses of sensilla trichodea type 1 to (Z,Z)‐3,9‐cis‐6,7‐epoxy‐octadecadiene, the most abundant component, showed an “all or none” pattern and the other two components showed sigmoidal dose‐response curves with a half threshold of 10^?4 (dilution equal to the concentration of 10 μg/μl). These results suggest that the major sex pheromone component functions as an on–off controller while secondary components function as modulators during olfactory transmission to the primary olfactory center.     

Field evaluation of female sex pheromone components of the cotton bollworm,Heliothis armigera

(Z)-11-hexadecenal and (Z)-9-hexadecenal were ineffective lures forH. armigera males unless combined. Attraction depended upon perception of a 90%–99% combination of (Z)-11-hexadecenal with 1%–10% (Z)-9-hexadecenal. Increasing the level of (Z)-9-hexadecenal in the mixture to 26.2% reduced catches. Adding 2.3% (Z)-7-hexadecenal to the mixture did not enhance or reduce attraction, while adding 8.7% (Z)-11-hexadecenol significantly reduced male catches. The combination of (Z)-11-hexadecenal and (Z)-9-hexadecenal was effective only when released from rubber dispensers but not from polyethylene vials. A load of 2 mg of the mixture on rubber dispensers effectively attracted males for at least 31 days. TheH. zea lure which contained all the pheromonal components of that species was also effective in attractingH. armigera males. TheH. virescens lure attracted significantly fewerH. armigera males than theH. zea lure.

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Résumé Les (Z)-11-hexadecenal et (Z)-9-hexadecenal sont des attractifs sexuels in efficaces pour les mâles deH. armigera. L'attraction dépend de la perception d'un mélange de 90 à 99% de (Z)-11-hexadecenal avec 1 à 10% (Z)-9-hexadecenal, L'augmentation jusqu'à 26,2% de la teneur en (Z)-9-hexadecenal réduit les captures. L'addition de 2,3% de (Z)-7-hexadecenal au mélange ne modifie pas l'attractivité, tandis que celle de 8,7% de (Z)-11-hexadecenol, réduit significativement les captures de mâles. Le mêlange de (Z)-11-hexadecenal et de (Z)-9-hexadecenal n'a été efficace qu'avec des diffuseurs en caoutchouc, par contre il a été sans effet à partir de récipients de polyéthylène. Une charge de 2 mg de mélange dans des diffuseurs en caoutchouc attire effectivement les mâles pendant ou moins 31 jours. L'attractif sexuel deH. zea qui contient tous les constituants de la phéromone de cette espèce attire aussi efficacement les mâles deH. armigera. Celui deH. virescens attire significativement moins de mâles deH. armigera que l'attractif sexuel deH. zea.

     

Incomplete electrical isolation of sex-pheromone responsive olfactory receptor neurons from neighboring sensilla

In the long trichoid sensilla on male Helicoverpa zea antennae, approximately 40% of the sensilla having a large-spiking olfactory receptor neuron responding to the major pheromone component, (Z)-11-hexadecenal, also exhibit small-spiking action potentials that also seem to be responsive to this same compound. In this study, we investigated whether these small-spiking signals are a result of intrusive electrical signals generated from neighboring sensilla. Two methods were used for this study. First, the sensillum was completely covered by the saline-filled recording electrode to physically prevent the sensillum from being contacted by exposure to (Z)-11-hexadecenal. In this case, activation of the large-spiking neuron in response to the pheromone component was prevented, whereas the small-spiking activity continued to be influenced by the airborne delivery of the pheromone. In the second method the (Z)-11-hexadecenal was applied directly in solution through the cut tip of the sensillum through the recording electrode. In this case only large-spiking activity occurred in response to (Z)-11-hexadecenal, with no increase whatsoever in the firing frequency of the small spikes. We conclude that these long trichoid olfactory sensilla are not completely isolated electrically from neighboring sensilla and that small spikes in some recordings originate from large-spiking olfactory receptor neurons (ORNs) in neighboring sensilla.     

Smoke,pheromone and kairomone olfactory receptor neurons in males and females of the pine sawyer Monochamus galloprovincialis (Olivier) (Coleoptera: Cerambycidae)

The response of antennal olfactory receptor neurons (ORNs) of Monochamus galloprovincialis to several odourants was tested using single sensillum electrophysiology. Behaviourally active pheromone, and kairomone (host and sympatric bark beetle pheromone) odours were tested alongside smoke compounds released by burnt wood that are potentially attractive to the insect. The antennae bore several types of sensilla. Two plate areas in the proximal and distal ends of each antennal segment were covered with basiconic sensilla that responded to the odour stimuli. Sensilla basiconica contained one or two cells of different spike amplitude. The 32 male and 38 female ORNs tested responded with excitations or inhibitions to the different plant odours. In general the response of male and female receptors was very similar so they were pooled to perform a cluster analysis on ORN responses. Six ORNs were clearly specialised for pheromone reception. Responses to kairomone and smoke odours were less specific than those of pheromone, but a group of 9 cells was clearly excited by smoke compounds (mainly eugenol and 4-methyl 2-methoxyphenol), a group of 8 cells was very responsive to α-pinene, β-pinene and cis-verbenol, and a group of 14 cells responded to a wider range of compounds. The rest of the cells (47%) were either non-responsive or slightly inhibited by smoke compounds. Dose–response curves were obtained for several compounds. Different compounds induced significantly different latencies and these appeared to be unrelated to their boiling point.     

Spatial organization of antennal olfactory sensory neurons in the female Spodoptera littoralis moth: differences in sensitivity and temporal characteristics

Single-cell recordings from olfactory sensory neurons (OSNs), housed in sensilla located at the base and at the tip of the antenna, showed selective responses to plant odors and female sex pheromone in this polyphagous moth. A spatial variation existed in sensitivity: OSNs present on the more proximal segment (P) were more sensitive than those on the more distal segment (D). OSNs of the 2 locations also differed in temporal characteristics: OSNs on P had shorter latency and displayed more phasic responses, whereas those on D had more tonic responses, especially at low stimulus concentrations. The 196 OSNs responding to our 35 monomolecular stimuli in the screening were housed in 32 functional sensillum types: 27 in basiconic, 3 in long-trichoid, 2 in coeloconic, and 3 in auricillic sensilla. The OSNs in basiconic, coeloconic, and auricillic sensilla responded to plant-associated odorants, whereas OSNs in long-trichoid sensilla responded to female-produced sex pheromone components. Short-trichoid sensilla showed spontaneous activity, but no responses to any odorant tested. OSN specificity to plant stimuli ranged from highly specific to broadly tuned, but it did not differ clearly from females in more specialized moths. OSN response diversity is discussed in terms of olfactory coding, behavior, and ecological specialization.