Altered olfactory receptor neuron responsiveness in rare Ostrinia nubilalis males attracted to the O. furnacalis pheromone blend

Three percent of E-strain Ostrinia nubilalis males fly upwind in response to the Ostrinia furnacalis pheromone blend [a 40:60 ratio of (E)-12-tetradecenyl acetate to (Z)-12-tetradecenyl acetate (E12-14:OAc to Z12-14:OAc)], in addition to their own pheromone blend [a 99:1 ratio of (E)-11-tetradecenyl acetate to (Z)-11-tetradecenyl acetate) (E11-14:OAc to Z11-14:OAc)]. We assessed the olfactory receptor neuron (ORN) responses of these behaviorally "rare" males versus those of normal males. For the three ORNs housed within each sensillum, we tested responsiveness to Z12-14:OAc, E12-14:OAc, Z11-14:OAc, E11-14:OAc, and the behavioral antagonist (Z)-9-tetradecenyl acetate (Z9-14:OAc). Z11-14:OAc, E11-14:OAc, and Z9-14:OAc stimulated ORNs exhibiting distinct small, large, and medium spike sizes, respectively. For rare and normal males, both Z12-14:OAc and E12-14:OAc usually elicited responses from the largest-spiking ORN. In many ORNs of normal males, Z12-14:OAc or E12-14:OAc stimulated the smaller-spiking ORN that is responsive to Z11-14:OAc. In rare males, detectable ORN responses from the smaller-spiking ORN in response to Z12- and E12-14:OAc were virtually non-existent. These differences in ORN tuning in rare males will tend to create an ORN firing ratio between the large- and small-spiking ORNs in response to the O. furnacalis blend that is similar to that elicited by the O. nubilalis blend.     

Effects of egg-to-adult development time and adult age on olfactory neuron response to semiochemicals in European corn borers

We used the cut-sensillum technique to assess the effect of both adult age and egg-to-adult development time on olfactory neuron responses of Z strain moths of the European corn borer, Ostrinia nubilalis. Compounds tested included the pheromone components, (Z)-11-tetradecenyl acetate and (E)-11-tetradecenyl acetate, the behavioral antagonist, (Z)-9-tetradecenyl acetate, and components of the O. furnicalis (Asian corn borer) sex pheromone, (Z)-12-tetradecenyl acetate and (E)-12-tetradecenyl acetate. The proportion of moths having neurons responding to the two O. nubilalis sex pheromone components and antagonist increased with longer development time and age. The spike frequency of neurons responding to (E)-11-tetradecenyl acetate and the antagonist increased with longer development time. Fourteen of 45 moths with neurons sensitive to either of the O. nubilalis pheromone components responded to (Z)-12-tetradecenyl acetate or (E)-12-tetradecenyl acetate. The likelihood of (Z)-12-tetradecenyl acetate stimulating a neuron similar in spike shape and waveform to that responding to (E)-11-tetradecenyl acetate increased with development time.     

Evidence of olfactory antagonistic imposition as a facilitator of evolutionary shifts in pheromone blend usage in Ostrinia spp. (Lepidoptera: Crambidae)

Olfactory receptor neuron (ORN) response was measured to assess why some males ("rare males") of the Asian corn borer (ACB), Ostrinia furnacalis, have a broad behavioral response to fly upwind to both the ACB and the European corn borer (ECB), Ostrinia nubilalis, pheromone blends. We performed single-sensillum electrophysiological recordings on ACB males that had been behaviorally assessed for upwind flight response to the ACB blend [60:40 (Z)-12-tetradecenyl acetate (Z12-14:OAc) to (E)-12-tetradecenyl acetate (E12-14:OAc)], as well as to ECB (Z-strain) and ECB (E-strain) blends [3:97 and 99:1 (Z)-11-tetradecenyl acetate (Z11-14:OAc) to (E)-11-tetradecenyl acetate (E11-14:OAc)]. Sensilla from all types of males had large- and small-spike-sized ORNs responding strongly to Z12- or E12-14:OAc, but weakly to Z11- and E11-14:OAc. In the majority of males ("normal males") that flew upwind only to the ACB blend, Z11-14:OAc elicited responses in an intermediate spike-sized ORN associated with behavioral antagonism that is mainly tuned to (Z)-9-tetradecenyl acetate (Z9-14:OAc). In the rare-type ACB males that flew to both the ACB and ECB pheromone blends, Z11-14:OAc did not stimulate this ORN. Increased responsiveness to ancestral pheromone components by ORNs associated with behavioral antagonism could be instrumental in reproductive character displacement, or in reinforcement and reproductive isolation during speciation by helping to increase assortative mating between males and females in derived populations that use novel sex pheromone blends.     

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.     

Behavioural and electrophysiological activity of unsaturated analogues of the pheromone tetradecyl acetate in the small ermine moth Yponomeuta rorellus

ABSTRACT In field-trapping experiments the unsaturated analogues ( E )-6-, ( E )-12-, and ( Z )-12-tetradecenyl acetate were as attractive to male Yponomeuta rorellus Latr. as the native pheromone component tetradecyl acetate. All four analogues attracted more males than virgin females did, whereas ( Z )-6-, ( E )-11-, ( Z )-10- and ( Z )-11-tetradecenyl acetate were essentially non-attractive. Addition of 1–30% of ( Z )-11-tetradecenyl acetate to the pheromone tetradecyl acetate reduced the attraction to less than 2%. Flight tunnel experiments with Y. rorellus confirmed the activity of the ( E )-6- and ( E )-12-tetradecenyl acetates and demonstrated the activity of ( E )-7-tetradecenyl acetate as well. These analogues elicited orientation behaviour, upwind flight and landing at the odour source as frequently as the native pheromone did. Single sensillum recordings from male Y. rorellus showed two types of cells in most sensilla. A large spike amplitude cell was stimulated by tetradecyl acetate and the unsaturated analogues ( E )-11-, ( E )-6- and ( E )-12-tetradecenyl acetate, and to a lower extent by the ( Z )-6-, ( Z )-11- and ( Z )-12-isomers. A cell with medium spike amplitude was stimulated by ( Z )-9-tetradecenyl and ( Z )-11-hexadecenyl acetate. Some sensilla contained a third cell firing with a small spike amplitude which was activated by ( Z )-11-tetradecenol. Thus the tetradecyl acetate receptor was stimulated not only by the behaviourally active analogues, but also by behavioural antagonists. The interaction of ( E )-11-tetra-decenyl acetate and tetradecyl acetate with the same antennal receptor cell was also demonstrated in Y.cagnagellus . Electrophysiological discrimination between behavioural attractants and antagonists and the role of behavioural antagonists in the interspecific relations between Y.rorellus and sympatric closely related species are discussed.     

Identification of the sex pheromone of Ostrinia palustralis

By means of gas chromatography with electroantennographic detection, gas chromatography-mass spectrometry and a series of bioassays, (E)-11-tetradecenyl acetate (E11-14:OAc) and (Z)-11-tetradecenyl acetate (Z11-14:OAc) at a ratio of 99:1 were identified as female sex pheromone components of Ostrinia palustralis. The average amounts of E11- 14:OAc and Z11-14:OAc in a single sex pheromone gland were 37.2±24.4 ng and 0.3±0.2 ng, respectively. In a wind-tunnel bioassay, the binary blend of E11- and Z11-14:OAc elicited the same male behavioral responses as did virgin females.     

Sex pheromone of the butterbur borer, Ostrinia zaguliaevi

The sex pheromone blend of the butterbur borer, Ostrinia zaguliaevi (Lepidoptera: Pyralidae) was analyzed by means of gas chromatography-electroantennographic detection (GC-EAD), GC-mass spectrometry and a series of wind-tunnel bioassays. Four EAD-active compounds were detected in the female sex pheromone gland extract, and these were identified as tetradecyl acetate (14:OAc), (Z)-9-tetradecenyl acetate (Z9-14:OAc), (E)-11-tetradecenyl acetate (E11-14:OAc) and (Z)-11-tetradecenyl acetate (Z11-14:OAc). The average amounts ± s.d. of the four compounds in a single sex pheromone gland were 7.9±3.7 ng, 10.1±3.2 ng, 1.1±0.5 ng and 11.6±5.1 ng, respectively. In a wind-tunnel bioassay, the ternary blend of Z9-, E11- and Z11-14:OAc at a ratio found in the sex pheromone gland (45:5:50) elicited the same behavioral responses from the males as did virgin females and pheromone gland extract. Removal of any single compound from the ternary blend significantly diminished the pheromonal activity, whereas addition of 14:OAc to the ternary blend had no effect on the males' behavioral responses. Therefore, it was concluded that the sex pheromone blend of O. zaguliaevi is composed of Z9-14:OAc, E11-14:OAc and Z11-14:OAc at a ratio of 45:5:50.     

Notes on New Zealand mammals 10. Effect of observer position on group size and level of aggression of mating brown hares

Abstract

The sex pheromones of two endemic New Zealand tortricid species were investigated. Females of the first species, Cnephasia jactatana, a pest of kiwifruit, were found to produce (Z)-11-tetradecenyl acetate (Z11-14:OAc) in their sex pheromone gland. When tested in the field, this compound on its own elicited significant catches of male C. jactatana. However, the addition of even very small amounts (0.3%) of the geometric isomer, (E)-11-tetradecenyl acetate (E11-14:OAc), to Z 11-14:OAc virtually suppressed trap catches. The sex pheromone of the second species, Merophyas leucaniana, was found to consist of a mixture of Z11-14:OAc, E11-14:OAc, tetradecyl acetate, and (Z)-11-tetradecenol. This species is morphologically very similar to the congeneric species, M. divulsana, the Australian lucerne leafroller. The sex pheromone of M. leucaniana is also very similar to that of the so-called “Z-type” of M. divulsana, which is now found in New Zealand. The pheromone components of C. jactatana and M. leucaniana are discussed in relation to those found in other tortricids.     

Electroantennogram responses of the European corn borer,Ostrinia nubilalis,to (Z)- and (E)-11-tetradecenyl acetates

Antennal responses of male European corn borer moths, Ostrinia nubilalis, to their two pheromone components, (Z)- and (E)-11-tetradecenyl acetates (tda), were studied. The electroantennogram (EAG) response was highest when the ventral side and lowest when the dorsal side of the antenna faced the air stream carrying the chemical stimulus. Repetitive stimulation with one of the isomers resulted in adaptation which affected the amplitude of response in subsequent tests of both (Z)- and (E)-11-tda. This suggested that the receptors for the two tda isomers are either identical or highly interactive. Mixtures of the two pheromone components did not elicit higher responses than the major component, (Z)-11-tda. A significant difference was observed between London and New York strains of this insect in their relative responses to (Z)- and (E)-11-tda. EAG responses of hybrids of these two strains resembled those for the New York strain.     

Relative attractiveness of incomplete and complete blends of synthetic pheromone to male obliquebanded leafroller (Lepidoptera: Tortricidae) moths in a flight tunnel and in apple orchards: implications for sex pheromone-mediated mating disruption of this species

The relative attractiveness of synthetic Choristoneura rosaceana (Harris) pheromone consisting of the major compound Z-11-tetradecenyl acetate (Z11-14:OAc), or the major compound plus one, two, or all three of the minor compounds E-11-tetradecenyl acetate (E11-14:OAc), Z-11-tetradecenol (Z11-14:OH), and Z-11-tetradecenal (Z11-14:Ald), in amounts similar to those in the natural pheromone, was compared in a flight tunnel and in apple orchards. In the flight tunnel, there was an increase in the proportion of moths that were activated when E11-14:OAc was combined with the main compound, but no detectible additional increases in response with the addition of Z11-14:OH and Z11-14:Ald. The time required for activation was twice as long when using the major compound than when using the major compound and one or more of the minor compounds. There was a trend of increase in the proportion of males initiating the take-off, lock-on, close-in, and touchdown phases of upwind flight when progressively more complete blends were used. The time required for the initiation of these behavioral phases was statistically similar for each treatment. The proportion of moths landing at the pheromone source was 10 times greater when using the complete blend than when using the main compound alone. Similar results were obtained in apple orchards, where the four-compound blend was 17-55 times more attractive than the main compound. The superior attractiveness of the four-compound pheromone compared with the major compound, or to the major compound plus the minor compound E11-14:OAc, suggests that it would be the most effective synthetic pheromone if competitive attraction were an important mechanism of disruption in this species.     

Sex pheromone biosynthesis in the tortricid moth Planotortrix excessana (Walker) involves chain-shortening of palmitoleate and oleate

Biosynthesis of the sex pheromone components, (Z)-5-tetradecenyl acetate (Z5-14:OAc) and (Z)-7-tetradecenyl acetate (Z7-14:OAc), was investigated in the New Zealand tortricid moth Planotortrix excessana (Walker) by fatty acid methyl ester (FAME) analysis of base-methanolyzed extracts of lipids in the sex pheromone gland and through application of various labelled fatty acids. Analysis of the base-methanolyzed gland extracts revealed common FAMEs, including methyl oleate and methyl palmitoleate, as well as the FAMEs of the putative precursors, methyl (Z)-5-tetradecenoate and methyl (Z)-7-tetradecenoate. Application of labelled, saturated fatty acids, myristic, palmitic, and stearic did not result in any significant incorporation of label into either of the unsaturated pheromone components, although label was incorporated into tetradecyl acetate (14:OAc). In contrast, application of labelled oleic acid resulted in incorporation of label into Z5-14:OAc but not into Z7-14:OAc or into 14:OAc, whereas application of labelled palmitoleic acid resulted in incorporation of label into Z7-14:OAc but not into Z5-14:OAc or 14:OAc. These data support a route for biosynthesis of Z5-14:OAc and Z7-14:OAc in this species by limited β-oxidation of the common fatty acyl moieties, respectively, oleate (involving two cycles of 2-carbon chain-shortening) and palmitoleate (involving only one cycle of 2-carbon chain-shortening), and apparently involving no desaturase (other than the common Δ9) specific to sex pheromone biosynthesis. Interestingly, P. excessana females biosynthesize the same component (Z5-14:OAc) from an entirely different route from that of the related species Ctenopseustis obliquana (which biosynthesizes Z5-14:OAc by Δ5-desaturation of myristate). Additionally, the pheromone biosynthesis activating neuropeptide (PBAN) stimulates pheromone biosynthesis in this species. Arch. Insect Biochem. Physiol. 37:158–167, 1998. © 1998 Wiley-Liss, Inc.     

The contribution of olfactory receptor neurons to the perception of pheromone component ratios in male redbanded leafroller moths

Summary (Z)-11-tetradecenyl acetate (Z-11, 14:AC) must be in a 1009 ratio with (E)-11-tetradecenyl acetate (E-11,14:AC) to produce maximal wing fanning and attraction in male redbanded leafrollers. Earlier electrophysiological studies had indicated that mixtures of these pheromone components elicited responses from olfactory receptor neurons that appeared to differ from those expected on the basis of the responses to the individual components. Here we evaluate whether the behavioral sensitivity to particular ratios of Z- and E-11,14:AC has a correlate in the response properties of olfactory receptor neurons.The stimuli included the ratios of Z- and E-11, 14:AC used in earlier behavioral work plus several different mixtures of the seven components found in the pheromone blend, and equivalent amounts of the individual components. These stimuli were presented over a range of intensities to individual trichoid sensilla on the male antenna. In common with earlier results, the receptor neuron with the larger amplitude action potential responded most strongly to Z-11,14:AC, whereas the companion receptor neuron in the sensillum responded most strongly to E-11,14:AC. In contrast with earlier results, each receptor neuron responded exclusively to its own most effective stimulus, without regard to the presence of any other compound. They failed to respond uniquely to any of the other five compounds in the female pheromone blend, or to any of the tested combinations of these compounds. These minor components also failed to modulate the responses elicited in receptor neurons by appropriate ratios of Z- and E-11,14:AC. Thus, the responses of the two types of olfactory receptor neurons found in trichoid sensilla failed to show an optimum at the pheromone ratio known to elicit peak behavioral activity.Abbreviation RBLR redbanded leafroller moth     

Identification of the Sex Pheromone of the Tree Infesting Cossid Moth Coryphodema tristis (Lepidoptera: Cossidae)

The cossid moth (Coryphodema tristis) has a broad range of native tree hosts in South Africa. The moth recently moved into non-native Eucalyptus plantations in South Africa, on which it now causes significant damage. Here we investigate the chemicals involved in pheromone communication between the sexes of this moth in order to better understand its ecology, and with a view to potentially develop management tools for it. In particular, we characterize female gland extracts and headspace samples through coupled gas chromatography electro-antennographic detection (GC-EAD) and two dimensional gas chromatography mass spectrometry (GCxGC-MS). Tentative identities of the potential pheromone compounds were confirmed by comparing both retention time and mass spectra with authentic standards. Two electrophysiologically active pheromone compounds, tetradecyl acetate (14:OAc) and Z9-tetradecenyl acetate (Z9-14:OAc) were identified from pheromone gland extracts, and an additional compound (Z9-14:OH) from headspace samples. We further determined dose response curves for the identified compounds and six other structurally similar compounds that are common to the order Cossidae. Male antennae showed superior sensitivity toward Z9-14:OAc, Z7-tetradecenyl acetate (Z7-14:OAc), E9-tetradecenyl acetate (E9-14:OAc), Z9-tetradecenol (Z9-14:OH) and Z9-tetradecenal (Z9-14:Ald) when compared to female antennae. While we could show electrophysiological responses to single pheromone compounds, behavioral attraction of males was dependent on the synergistic effect of at least two of these compounds. Signal specificity is shown to be gained through pheromone blends. A field trial showed that a significant number of males were caught only in traps baited with a combination of Z9-14:OAc (circa 95% of the ratio) and Z9-14:OH. Addition of 14:OAc to this mixture also improved the number of males caught, although not significantly. This study represents a major step towards developing a useful attractant to be used in management tools for C. tristis and contributes to the understanding of chemical communication and biology of this group of insects.     

Sex pheromone analysis and effective attraction of males of the cabbage webworm,Hellula undalis,inhabiting the Mekong Delta of Vietnam

Hellula undalis is a harmful insect pest of green mustard in the Mekong Delta of Vietnam. In order to establish a tool for a sustainable pest control program, the sex pheromone of H. undalis inhabiting the Mekong Delta was examined. GC-EAD and GC–MS analyses of pheromone gland extracts from the virgin females elucidated three new components, (Z)-11-tetradecenyl acetate (Z11-14:OAc), (Z)-11-hexadecenal (Z11-16:Ald), and (11E,13E)-11,13-hexadecadien-1-ol, in addition to the known pheromone component (11E,13E)-11,13-hexadecadienal (E11,E13-16:Ald). Double bond positions of the two monoenyl components were determined by GC–MS analysis of the pheromone extract treated with dimethyl disulfide. On the other hand, GC–MS analysis of the female body extract detected the unsaturated hydrocarbon (3Z,6Z,9Z)-3,6,9-tricosatriene (Z3,Z6,Z9-23:H). Field examinations of their synthetic compounds indicated the significant role of E11,E13-16:Ald as a major component and a clear synergistic effect of the two monoenyl compounds as a minor component. Although the 3:3:7 mixture of Z11-14:OAc, E11-16:Ald, and E11,E13-16:Ald captured the largest number of males among the tested mixtures, the activity was still quite a bit lower than that of virgin females. However, the 3:3:7:1 mixture, which was prepared by adding a small amount of Z3,Z6,Z9-23:H to the 3:3:7 ternary lure, succeeded in attracting males more powerfully than the females did. This strong synergistic effect was not observed when the triene was added to unmixed E11,E13-16:Ald, indicating important roles of not only the triene but also the two monoenyl compounds as natural pheromone components.     

Sex pheromone biosynthesis in Ostrinia zaguliaevi, a congener of the European corn borer moth O. nubilalis

In order to clarify the biochemical basis to the divergence of sex pheromones in the genus Ostrinia (Lepidoptera: Crambidae), the pheromone biosynthetic pathway in O. zaguliaevi, a close relative of the European corn borer O. nubilalis, was investigated. Deuterium-labeled hexadecanoic or tetradecanoic acids were topically applied to the surface of the pheromone gland, and the incorporation of the label into pheromone components and their putative precursors was determined. It was suggested that the two components shared by O. zaguliaevi and O. nubilalis, (E)-11- and (Z)-11-tetradecenyl acetates, are biosynthesized from hexadecanoic acid through one round of chain shortening, Delta11 desaturation, reduction, and acetylation. An additional component specifically found in O. zaguliaevi, (Z)-9-tetradecenyl acetate, is likely to be produced by delta11 desaturation of hexadecanoic acid, one round of chain shortening, reduction, and acetylation. Non-production of (Z)-9-tetradecenyl acetate in O. nubilalis was suggested to be due to the blockage of chain shortening from (Z)-11-hexadecenoate to (Z)-9-tetradecenoate.     

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.     

Electroantennogram response gradient on the antenna of the European corn borer, Ostrinia nubilalis

The electroantennogram (EAG) response of male moths of the European corn borer (Ostrinia nubilalis) to their two pheromone components, (Z)- and (E)-11-tetradecenyl acetates, were studied. The EAG amplitude of the fast initial phase was approximately proportional to the antennal length. Local EAG responses were obtained along the length of the antenna with multiple electrodes. Response-interaction studies indicated a unique spread of the EAG response in a proximal direction in the antenna. A possible mechanism of the EAG summation was considered. The EAG response characteristic was similar for both (Z)- and (E)-11-tetradecenyl acetate along the length of the antenna.     

Inheritance of central neuroanatomy and physiology related to pheromone preference in the male European corn borer

Background  

The European corn borer (ECB), Ostrinia nubilalis, is a textbook example of pheromone polymorphism. Males of the two strains (Z and E) prefer opposite ratios of the two pheromone components, Z11- and E11-tetradecenyl acetate, with a sex-linked factor underlying this difference in preference. The male antennal lobes of the two strains contain a pheromone sensitive macroglomerular complex (MGC) that is identical in morphology, but reversed in functional topology. However, hybrids prefer intermediate ratios. How a topological arrangement of two glomeruli can accommodate for an intermediate preference was unclear. Therefore we studied the neurophysiology of hybrids and paternal backcrosses to see which factors correlated with male behavior.