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.     

Response specificity of male olfactory receptor neurones for the major and minor components of a female pheromone blend

Abstract The sex attractant of the female redbanded leafroller moth, Argyrotaenia velutinana (Walker), is a blend of seven compounds. Specialized olfactory receptor neurones had been found for only two of the compounds, (Z)-11-tetradecenyl acetate (Z11-14:Ac) and (E)-11-tetradecenyl acetate (E11–14:Ac). These receptor neurones were always found in pairs within the long trichoid sensilla, which are the most abundant multi-pored sensilla on the male antenna. A systematic survey of all regions of the male antenna with standard extracellular recording techniques was undertaken to find receptor neurones responsive to the remaining five minor components of the female pheromone. Of the 113 long trichoid sensilla sampled, all contained two receptor neurones, one specialized for Z11–14:Ac and a second specialized for Ell –14:Ac. A comparable number of recordings were then obtained from the less abundant classes of multi-pored sensilla. Two new receptor neurone types were found, responsive to the minor pheromone components (E)-9-dodecenyl acetate (E9-12:Ac) and (Z)-9-dodecenyl acetate (Z9-12:Ac). Scanning electron micrographs indicated that these recordings were obtained from shorter, narrower trichoid sensilla. The majority of these sensilla appeared to contain three neurones capable of spontaneous action potential production. In each sensillum, only one receptor neurone appeared to respond to stimulation with a minor component of the female blend. The remaining two neurones did not respond to the chemical stimuli evaluated.     

Behavioral observations of codling moth, Cydia pomonella, in orchards permeated with synthetic pheromone

Mating disruption of codling moth, Cydia pomonella, was studied in apple orchards treated with the main pheromone compound codlemone, (E,E)-8,10-dodecadienol, and a blend of codlemone and codlemone acetate, (E,E)-8,10-dodecadienyl acetate, a strong pheromone antagonist. Codlemone alone and the pheromone/antagonist-blend had a similar effect on the behavior of males emerging into air-permeated orchards. Male flights within tree canopy and upwind orientation along tree rows were strongly enhanced by both formulations, compared to untreated plots. However, the codlemone/codlemone acetate-blend increased the rate of cross-wind and downwind flights within the orchard, compared to codlemone alone. The major difference between these two formulations was that males from nearby, untreated orchards were attracted towards orchards treated with codlemone, but not towards treatments with codlemone/codlemone acetate. Additional tests were done with an equilibrium blend of codlemone and its geometric isomers. Aerial pheromone concentrations in the orchards were recorded by the field electroantennogram technique. Decreasing pheromone concentrations towards the upper part of the tree canopy, together with the stimulation of male flight activity by synthetic pheromone explains failures to control codling moth at high population densities with current dispenser formulations.     

Plant-odour-specific receptor neurones on the antennae of female and male Spodoptera littoralis

Abstract. Receptor neurones with high selectivity and sensitivity to plant odours were found within short sensilla trichodea on the antenna of both female and male Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) by using single-sensillum recording techniques. In 112 sensilla from females and forty-one from males, twenty-four different receptor neurone types were characterized according to their specificity. Altogether, twenty-six plant and three sex pheromone compounds were tested. Receptor neurones responding with high specificity to flower odours, green leaf volatiles, oviposition deterrents and other general host plant odours were identified. In twenty-one receptor neurone types, responses were elicited by one or several plant compounds, and in three types responses were elicited by sex pheromone compounds. The majority of the receptor neurones responded to only one or two of the tested compounds. In general, only one of the two receptor neurones in a sensillum responded to any of the compounds tested. An exception was a receptor neurone responding to plant odours (green leaf volatiles) and another receptor neurone responding to a sex pheromone compound ([Z]-7-dodecenyl (acetate), which occurred in the same sensillum. The majority of the receptor neurones displayed a high sensitivity to plant odours. No morphological difference was identified the different sensillum types.     

Spatial organization of olfactory receptor neurons on the antenna of the cabbage looper moth

Electrophysiological responses to stimulation with behaviorally relevant compounds were recorded from receptor neurons within specialized classes of sensilla on the antennae of male cabbage looper moths. Receptor neurons were found that specifically respond to stimulation with Z-7,12:AC, Z-7,14:AC, Z-9,14:AC, and Z-7,12:OH. Specialized receptor neurons were not found for the three remaining pheromone blend components, 12:AC, Z-5,12:AC, or 11,12:AC. However, a new class of sensillum containing a pair of neurons insensitive to all of the cabbage looper pheromone components was encountered. In addition, spatial patterns of distribution along the flagellum for identified classes of sensilla are described. Sensilla containing Z-7,12:AC-sensitive neurons are preferentially located on the proximal half of the antennal flagellum. In addition to this distribution along the length of the antenna, a pattern across individual flagellar subsegments is described. Sensilla containing neurons sensitive to Z-9,14:AC were found exclusively on the lateral margins of individual flagellar subsegments. Accepted: 19 June 1998     

Olfactory neuron responsiveness and pheromone blend preference in hybrids between Ostrinia furnacalis and Ostrinia nubilalis (Lepidoptera: Crambidae)

The olfactory receptor neuron (ORN) and behavioral responses of hybrids between the Asian corn borer (ACB), Ostrinia furnacalis, and the E-strain European corn borer (ECB(E)), Ostrinia nubilalis were examined and compared to the parental populations. In hybrids and both parents, the large-spike-size ORN was capable of responding to all four pheromone components of ACB and ECB, despite differences in which compounds elicited the greatest spike frequency in each population. There was a small-spiking ORN more narrowly tuned to the minor pheromone components in both ACB and ECB(E). In hybrids the homologous small-spiking ORN was tuned primarily to the ECB(E) minor pheromone component, with some responsiveness to the ACB minor component. Both species and all the hybrids had an intermediate spike-size ORN tuned primarily to their common behavioral antagonist. Dominance of responsiveness to the ECB(E) versus the ACB minor pheromone component on the small-spiking ORN may explain the greater tendency of hybrids to fly upwind to the ECB(E) pheromone blend than the ACB blend. This finding points toward a distinct evolutionary role for this ORN in allowing a pheromone shift.     

麻疯树柄细蛾触角及其感器的扫描电镜观察

应用扫描电镜对麻疯树柄细蛾Stomphastis thraustica Meyrick成虫触角的外部形态结构及其感器进行了观察和研究。结果表明,麻疯树柄细蛾成虫触角上存在着5种感器即毛形感器、刺形感器、腔椎形感器、锥形感器和鳞形感器。对各种感器的形态特点进行描述,其中毛形感器数量最多,并分为长毛形和短毛形2种。刺形感器也分为长刺形和短刺形2种。     

Electrophysiological and behavioural evidence for a fourth sex pheromone component in the turnip moth, Agrotis segetum

Abstract. In addition to the pheromone components (Z)-5-decenyl, (Z)-7-dodecenyl and (Z)-9-tetradecenyl acetate (Z5-10:OAc, Z7-12:OAc and Z9-14:OAc), it has previously been shown that the sex pheromone gland of the turnip moth, Agrotis segetum (Lepidoptera: Noctuidae Schiff) contains 10:OAc, 12:OAc, Z5-12:OAc, Z9-12:OAc, 11–12:OAc, Z5-14:OAc, Z7-14:OAc and Z11-16:OAc. To find out whether any of these additional compounds is involved in the sex pheromone communication in A. segetum, a comprehensive electro-physiological and behavioural investigation was conducted. Single-sensillum recordings on male antennae revealed three subtypes of sensilla among the previously so-called Z5-10:OAc sensilla. One subtype was identified having one receptor neurone (A) that responded to Z5-10:OAc with a large spike amplitude and another neurone (B) that responded to (Z)-5-decenol (Z5-10:OH) with a small spike amplitude. In another subtype the B neurone responded to Z5-12:OAc and sometimes also to 27-12:OAc and 10:OAc, in addition to responding to Z5-10:OH. In a third subtype the A neurone responded to all acetates identified from the female pheromone gland, whereas the small spike amplitude neurone was tuned to Z5-10:OH. A flight tunnel assay showed that blends composed of nine, eight or seven compounds were equivalent to the previously identified three-component pheromone blend in eliciting male behavioural responses. In field trapping tests, blends of eleven, nine or seven compounds did, however, catch significantly more moths than the three-component blend. Further assays showed that only 25- 12:OAc could significantly increase the catch numbers when added to the three-component blend, and thus qualified as a fourth pheromone component in A. segerum. The behavioural significance of additional female-produced acetates — for which males possess antennal receptors — is suggested, but may be impossible to confirm because of ‘diminishing returns’ when trying to refine a multicomponent pheromone further.     

Interference of plant volatiles on pheromone receptor neurons of male Grapholita molesta (Lepidoptera: Tortricidae)

In moths, sex pheromone components are detected by pheromone-specific olfactory receptor neurons (ph-ORNs) housed in sensilla trichodea in the male antennae. In Grapholita molesta, ph-ORNs are highly sensitive and specific to the individual sex pheromone components, and thus help in the detection and discrimination of the unique conspecific pheromone blend. Plant odors interspersed with a sub-optimal pheromone dose are reported to increase male moth attraction. To determine if the behavioral synergism of pheromone and plant odors starts at the ph-ORN level, single sensillum recordings were performed on Z8-12:Ac and E8-12:Ac ph-ORNs (Z-ORNs and E-ORNs, respectively) stimulated with pheromone–plant volatile mixtures. First, biologically meaningful plant-volatile doses were determined by recording the response of plant-specific ORNs housed in sensilla auricillica and trichodea to several plant odorants. This exploration provided a first glance at plant ORNs in this species. Then, using these plant volatile doses, we found that the spontaneous activity of ph-ORNs was not affected by the stimulation with plant volatiles, but that a binary mixture of sex pheromone and plant odorants resulted in a small (about 15%), dose-independent, but statistically significant, reduction in the spike frequency of Z-ORNs with respect to stimulation with Z8-12:Ac alone. The response of E-ORNs to a combination of E8-12:Ac and plant volatiles was not different from E8-12:Ac alone. We argue that the small inhibition of Z-ORNs caused by physiologically realistic plant volatile doses is probably not fully responsible for the observed behavioral synergism of pheromone and plant odors.     

Antennal responses of Cydia pomonella (L.) exposed to surfaces treated with methoxyfenozide

Electroantennogram (EAG) measurements were recorded from the antennae of male and female codling moth, Cydia pomonella L., to determine whether adult moths exposed to surfaces treated with the ecdysteroid agonist methoxyfenozide experience a decline in their antennal reception and thus olfactory sensitivity. Such a phenomenon would offer a possible mechanism for the previously reported decreased responsiveness from moths treated with methoxyfenozide to pheromone‐ and plant volatile‐based monitoring lures. Mean EAG data revealed that the antennae from methoxyfenozide‐treated male moths appear to be just as sensitive to various doses of synthetic codlemone as the antennae from the control and surfactant‐treated moths, but they appeared to be less sensitive to the pheromone component 12OH (collected from female effluvia) than the control male antennae. Mean male EAG responses to the pheromone components E8,E10‐12Al and codlemone collected from methoxyfenozide‐treated females were significantly less than the responses towards those two pheromone components collected from the control and surfactant‐treated females. Female moth exposure to methoxyfenozide did not negatively impact the sensitivity of female antennae to the plant volatile pear ester, but it did towards the apple volatile butyl hexanoate. Data from this study show that adult C. pomonella exposure to methoxyfenozide‐treated surfaces does appear to negatively impact, in a minor way, the (i) olfactory sensitivity (or detection) of male antennae towards some components of the female sex pheromone, (ii) the female antennal sensitivity towards a key apple volatile and (iii) the attractiveness of female pheromone effluvia.     

Electrophysiological response to herbivore-induced host plant volatiles in the moth Spodoptera littoralis

In cotton, Gossypium hirsutum (Malvacae), the volatiles emitted from the plant change in response to herbivory. Ovipositing females of the Egyptian cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) can discriminate between cotton plants subjected to larval feeding and undamaged plants during oviposition. In this study we investigate whether females of this moth can detect the herbivore-induced cotton volatiles. The response of female S. littoralis antennae to volatiles collected from cotton plants subjected to larval feeding was studied using GC-EAD (coupled gas chromatography electroantennographic-detection). By GC-EAD, responses to over 10 different cotton volatiles were observed. Using single sensillum technique the responses of short sensilla trichodea on the antennae of S. littoralis females to 19 cotton volatiles and 12 general plant volatiles were investigated. Responses to these volatiles were recorded from 108 receptor neurones. Several neurones activated by herbivore-induced cotton volatiles were recorded. For example, a neurone type responding to two homoterpenes [(E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene and (E)-4,8-dimethyl-1,3,7-nonatriene] and (E,E)-α-farnesene was frequently found. We also observed sensitive neurones responding specifically to the herbivore-induced volatiles (+/–)-linalool and indole. In general, a stimulus load of less than 1 ng was needed to activate these neurones. In addition, specific neurones were found for constitutive cotton volatiles released in connection with damage to the plant. An abundant neurone type responded to β-caryophyllene and α-humulene. Another neurone type responded specifically to the non-induced cotton volatile (Z)-jasmone. These results show that females of S. littoralis have receptor neurones that would make it possible to discriminate between damaged and undamaged plants using volatile signals.     

Selective receptor neurone responses to E-β-ocimene, β-myrcene, E,E-α-farnesene and homo-farnesene in the moth Heliothis virescens, identified by gas chromatography linked to electrophysiology

An important question in olfaction is for which odorants receptor neurones have evolved. In the present study, olfactory receptor neurones on the antennae of the tobacco budworm moth Heliothis virescens were screened for sensitivity to naturally occurring plant-produced volatiles by the use of gas chromatography linked to electrophysiology. Volatiles of host as well as non-host plants collected by headspace techniques were used for stimulating the neurones, sequentially via two columns, one polar and one nonpolar installed in parallel in the gas chromatograph. Three types of neurones presented in this paper responded to one, two or three compounds for which the retention times were determined in both column types. The chemical structures of the active components were determined on the basis of mass spectrometry linked to gas chromatography, indicating E-beta-ocimene and beta-myrcene as stimulants for neurone type 1, E,E-alpha-farnesene for neurone type 2 and homo-farnesene for neurone type 3. Re-testing authentic materials verified the identifications for the type 1 neurones. The results demonstrate a high specificity for the three types of neurones by strong responses to one or two structurally similar compounds out of hundreds present in a large variety of plants. The study exemplifies plant odour detection by narrowly tuned receptor neurones in a polyphagous moth species.     

Correlation between dendrite diameter and action potential amplitude in sex pheromone specific receptor neurons in male Ostrinia nubilalis (Lepidoptera: Pyralidae)

Outer dendritic segments of olfactory receptor neurons tuned to sex pheromone components were measured morphometrically on the antenna of male European corn borers. Ostrinia nubilalis, to determine if a correlation exists between the diameter of the outer dendritic segment and the spike amplitude. The olfactory sensilla investigated each contained three receptor cells. Two cells were each specific for one of the two pheromone components, (Z)-11-tetradecenyl acetate (Z11-14:OAc) and (E)-11-tetradecenyl acetate (E11-14:OAc). Two strains of cornborers (Z and E) differ as to which of the two pheromone components is the main one. In both strains a large difference could be observed between the spike amplitudes elicited in the receptor cells by the two pheromone components, the main component always eliciting the large spike. In F1-hybrids (EZ) of these two strains, producing both pheromone components in similar quantities, the spike amplitudes were equal in the two pheromone-specific receptor cells. The third cell responded specifically to a behavioural antagonist. (Z)-9-tetradecenyl acetate (Z9-14:OAc) in both the parental and hybrid strains, and always showed the smallest spike amplitude. In a morphometric study, the outer dendritic segments were shown to differ more in diameter between the largest and second largest cell in the two parental strains than in the hybrid strain, while the smallest diameter cell did not differ between the different strains. These results imply that receptor cells with larger diameter produce spikes with greater amplitude. The data also show that all three types of receptor neurons display outer dendritic segments with strong variation in the diameter along the length of the segment, and with a pronounced taper towards the tip.     

Relationship between sex pheromone elicited behaviour and response of single olfactory receptor neurones in a wind tunnel

Responses from pheromone‐specific receptor neurones in male Agrotis segetum (Denis & Schiffermüller) (Lepidoptera: Noctuidae) were recorded in a laboratory wind tunnel. Stimuli were: (1) rubber septum dispensers loaded with single components or a four‐component pheromone blend, (2) excised glands from female A. segetum, (3) constrained A. segetum females with extruded glands. Dose–response curves for three neurone‐types with different specificity were established. The neurones were specifically tuned to respond to either one of the two pheromone components (Z)‐5‐decenyl acetate and (Z)‐7‐dodecenyl acetate, or to the behavioural antagonist (Z)‐5‐decenol. In parallel, a behavioural dose–response curve with males flying upwind to a four‐component pheromone blend was established. There was a clear correlation between behavioural arrestment of upwind flight and maximum spiking activity in Z5–10:OAc‐specific neurones. The pheromone release rates of individual females and synthetic dispensers were compared. A load of 50–200 ng of Z5–10:OAc on a rubber septum elicited approximately the same neural response as one female gland.     

Sex pheromone of Argyrotaenia pomililiana (Lepidoptera: Tortricidae), a leafroller pest of apples in Argentina

Sex pheromone gland extracts of Argyrotaenia pomililiana Trematerra & Brown females contained seven 14-chain compounds, the Z and E isomers of 11-tetradecenyl acetate, 11-tetradecen-1-ol, and 11-tetradecenal, respectively, together with tetradecyl acetate. In field trapping tests, a 100:5 blend of Z11-14:Ac and Z11-14:Al was shown to be suitable for detection and monitoring of A. pomililiana. This species-specific lure will facilitate the use of mating disruption against codling moth, Cydia pomonella (L.), in Argentine fruit orchards.     

Detection of sex pheromone components in Manduca sexta (L.).

The ability of olfactory receptor neurons to detect female-produced sex pheromone components and a limited sample of potential host plant odours was studied by single-sensillum recordings from olfactory sensilla present on male and female antennae in Manduca sexta. The majority of pheromone-sensitive receptor neurons examined in males was specialized for detection of the two major pheromone components, E10,Z12-hexadecadienal and E10,E12,Z14-hexadecatrienal or E10,E12,E14-hexadecatrienal. New olfactory receptor neurons tuned to the minor components E10,E12-hexadecadienal and Z11-hexadecenal were found. In females, olfactory receptor neurons specific to Z11-hexadecanal were discovered. Pheromone components and host volatiles were detected by separate sets of receptor neurons.     

A portable electroantennogram sensor for routine measurements of pheromone concentrations in greenhouses

Mating disruption using pheromone dispensers is an emerging insect control method in greenhouses in the Netherlands. For routine measurements of the pheromone level in greenhouses a portable and compact device based on electroantennography (EAG) was developed. The instrument was tested in different greenhouses under varying conditions using antennae of males of the noctuid moth Chrysodeixis chalcites. Relative differences in pheromone concentration between greenhouses loaded with pheromone dispensers and control greenhouses could be measured in a reliable way. Changes in pheromone concentration were clearly demonstrated by measurements during the growing season. The advantages of the instrument presented over previously described devices are its true portableness, ease of use and uncomplicated measuring principle. The device can be operated routinely by non-experts, and many measurements can be made in a short period of time. Preliminary outdoor measurements using antennae of male Cydia pomonella as sensor showed the potential of the instrument for use in the open field. The portable EAG sensor described here may provide a practical means for monitoring pheromone concentration and dispersal from dispensers applied for mating disruption.     

Antennal sensilla of male and female Telenomus reynoldsi gordh and coker (Hymenoptera : Scelionidae)

Sensilla on the antennae of both sexes of Telenomus reynoldsi (Hymenoptera : Scelionidae) were studied with the scanning electron microscope to determine their structure and possible function in mating and host recognition. Two types of setiform sensilla occur: curved, grooved sensilla trichodea and erect, stout sensilla chaetica. Horn-like sensilla trichodea curvata are abundant on the male antennae, but are less abundant and only present dorsally on the female. Sensilla basiconica are unique to the ventral surface of the apical 4 segments of the female antennae. Sensilla styloconica are located on A4 and A10 of the female and A7 and A9 of the male. Multiporous grooved sensilla are present on A4, A6, and A11 of the female and A4 and A6-A11 of the male. A possible sex gland is located on the venter of A5 of the male. The functions of sensilla trichodea curvata and sensilla basiconica in courtship and host recognition, respectively, are hypothesized by correlation with behavioral observations.     

Sex pheromone biosynthesis in the pine caterpillar moth, Dendrolimus punctatus (Lepidoptera: Lasiocampidae): pathways leading to Z5-monoene and 5,7-conjugated diene components

Biosynthesis of the sex pheromone components (Z)-5-dodecenol and (Z,E)-5,7-dodecadienol in Dendrolimus punctatus was studied by topical application of deuterium-labeled fatty acids to pheromone glands and subsequent analysis of fatty acyl groups and pheromone components by gas chromatography-mass spectrometry. Our studies suggest that both (Z)-5-dodecenol and (Z,E)-5,7-dodecadienol can be biosynthetically derived from chain elongation of palmitate to stearate in the gland, and its subsequent Delta11 desaturation to produce (Z)-11-octadecenoate. After three cycles of 2-carbon chain-shortening, the pheromone glands produce (Z)-5-dodecenoate, which is then converted to (Z)-5-dodecenol by reduction. A second Delta11 desaturation of (Z)-9-hexadecenoate produces (Z,E)-9,11-hexadecadienoate, which is then chain shortened in two cycles of beta-oxidation and finally converted to (Z,E)-5,7-dodecadienol by reduction.