|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
First published online December 1, 2006
Journal of Experimental Biology 209, 4946-4956 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02587
Unusual response characteristics of pheromone-specific olfactory receptor neurons in the Asian corn borer moth, Ostrinia furnacalis
1 Division of Chemical Ecology, Department of Crop Science, Swedish
University of Agricultural Sciences, SE-230 53 Alnarp, Sweden
2 Laboratory of Applied Entomology, Graduate School of Agricultural and Life
Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
3 Institute of Plant Physiology and Ecology, Shanghai Institutes for
Biological Sciences, Chinese Academy of Sciences, Shanghai 200032,
China
4 Department of Ecology, Lund University, SE-223 62 Lund, Sweden
* Author for correspondence at present address: Department of Forest Entomology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8634, Japan (e-mail: takanasi{at}affrc.go.jp)
Accepted 5 October 2006
 |
Summary |
|---|
 TOP Summary IntroductionMaterials and methodsResultsDiscussionReferences |
|---|
The peripheral pheromone detection system of O. furnacalis is
different to that of other moths. A large majority of the neurons investigated
responded to both of the two principal pheromone components. Dose-response and
cross-adaptation studies showed that olfactory receptor neurons with large
amplitude action potentials responded equally well to E12- and Z12-14:OAc in
sensillum types 1-3. Field experiments showed that O. furnacalis
males are sensitive to ratios of E12- and Z12-14:OAc and that
(Z)-9-tetradecenyl acetate acts as a behavioral antagonist. O.
furnacalis males thus display an unusual coding system for odors involved
in sexual communication, mainly built on less specific neurons, but still have
the ability to detect and respond to the correct female blend. We hypothesize
that the pheromone detection system of O. furnacalis consists of two
parts, where one is devoted to high sensitivity to 
12 isomers of
tetradecenyl acetate, E12- and Z12-14:OAc and the other to highly specific
responses to the E12- or Z12-14:OAc. The unusual feature is thus that a large
part of the system is devoted to sensitivity and only a minor part to
selectivity. This could be explained by the fact that no other moth species
are known to use E12- and/or Z12-14:OAc and that no strong selective pressure
to increase selectivity between the isomers has been determined.
Key words: olfaction, electrophysiology, single sensillum recording, Ostrinia nubilalis, sex pheromone communication, behavioral antagonist, field trapping, electron microscopy
|
Introduction |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
;
Todd and Baker, 1999).
Moth species in the genus Ostrinia (Lepidoptera: Crambidae) mainly
use isomers of tetradecenyl acetates for sex pheromone communication (for a
review, see Ishikawa et al.,
1999b). O. furnacalis and sympatric congeners O.
scapulalis, O. zaguliaevi and O. zealis occur in Asia,
whereas the European corn borer, O. nubilalis, occurs in Europe and
North America. Field trapping and wind-tunnel experiments have shown that
O. furnacalis is unique in utilizing (E)-12- and
(Z)-12-tetradecenyl acetates (E12- and Z12-14:OAc, hereafter
abbreviated accordingly), whereas the other species have (E)-11- and
(Z)-11-tetradecenyl acetates (E11- and Z11-14:OAc) as pheromone
components (Klun et al., 1975;
Klun et al., 1980;
Huang et al., 1997;
Zhou and Du, 1999). In
addition, (Z)-9-tetradecenyl acetate (Z9-14:OAc) is a pheromone
component of O. zaguliaevi and O. zealis
(Huang et al., 1998b;
Ishikawa et al., 1999a). This
compound also functions as a behavioral antagonist in O. nubilalis
and O. scapulalis (Glover et al.,
1989; Ishikawa et al.,
1999a).
Sex pheromone communication of the Asian corn borer, O.
furnacalis, has been studied intensely because of its status as a serious
pest of maize in Asian countries. Ando et al. characterized the sex pheromone
in Japan as E12- and Z12-14:OAc at a blend ratio of 
40% E and 60% Z
isomer (Ando et al., 1980).
Female pheromone blends differ slightly in four Japanese populations (35-43% E
isomer) (Huang et al., 1998a).
Concordant with variations in the female pheromone blend composition,
field-trapping experiments have shown an optimal male behavioral response to a
blend containing 36% E12-14:OAc in a Japanese population
(Huang et al., 1998a). There
are other reports of similar variations in female pheromone blend and male
behavioral response in populations in other Asian countries
(Kou et al., 1992;
Boo and Park, 1998).
In O. nubilalis, two strains are attracted by pheromone blends
dominated by E11- and Z11-14:OAc, respectively
(Glover et al., 1987;
Glover et al., 1989;
Cossé et al., 1995;
Linn et al., 2003). In both
strains, two different receptor neurons respond specifically to one of the two
pheromone components, and a third neuron responds to Z9-14:OAc
(Hansson et al., 1987;
Hansson et al., 1994;
Cossé et al., 1995). The
pheromone-specific receptor neurons reside in trichoid sensilla on the antenna
and can always be distinguished by their amplitude, so that the
large-amplitude neuron responds to the dominating pheromone component. Males
could thus be typed according to these physiological characteristics
(Hansson et al., 1987;
Hansson et al., 1994;
Cossé et al., 1995). In
addition, interneurons responding to each pheromone component and the
pheromone blend specifically occur in the male antennal lobe
(Anton et al., 1997). In O.
furnacalis, electroantennogram (EAG) responses to the pheromone
components E12- and Z12-14:OAc and pheromone components of other
Ostrinia species (Z9-, E11- and Z11-14:OAc) have been recorded
(Ando et al., 1980). However,
the EAG responses do not provide any bases to suggest how pheromone components
are distinguished by the peripheral olfactory system, even though behavioral
experiments have revealed the importance of the ratio between the components
(Huang et al., 1998a;
Boo and Park, 1998;
Zhou and Du, 1999).
Löfstedt and Hansson reported that pheromone receptor neurons of hybrid
males between O. nubilalis and O. furnacalis responded to
pheromone components of both species
(Löfstedt and Hansson,
1989). However, detailed information regarding receptor neuron
responses in O. furnacalis is absent. The external and internal
morphology of sensilla on the antenna of O. nubilalis has been
described, whereas only the external morphology has been described in O.
furnacalis (Ren et al.,
1987; Hallberg et al.,
1994).
In the present study, we observed the structure of the antenna and its sensilla in male O. furnacalis by scanning and transmission electron microscopy. We then recorded male olfactory receptor neuron responses to conspecific sex pheromone components (E12- and Z12-14:OAc) and to pheromone components of other Ostrinia species (Z9-, E11- and Z11-14:OAc) by using a cut-sensillum technique. Pheromone-specific olfactory receptor neurons were found in sensilla trichodea and were characterized by the size of their action potentials. An unusual coding system for pheromone information characterized by a large number of less specific neurons was revealed. In addition, field-trapping experiments were performed to investigate the effect of Z9-14:OAc as a behavioral antagonist.
|
Materials and methods |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
). The
culture originated from progenies of three female moths collected at Iruma
(35.5°N, 139.2°E), Saitama, Japan in 2001 by J. Tabata. All stages of
insects were kept at 25°C and 70% relative humidity with a 16 h:8 h L:D
cycle. Pupae were collected from the diet and the sex was determined. The
sexes were allowed to eclose separately. Male adults were provided with sugar
water and were used for electrophysiological recordings two to five days after
emergence.
Chemicals
All compounds tested [(E)-12-tetradecenyl acetate (E12-14:OAc),
(Z)-12-tetradecenyl acetate (Z12-14:OAc), (Z)-9-tetradecenyl
acetate (Z9-14:OAc), (E)-11-tetradecenyl acetate (E11-14:OAc),
(Z)-11-tetradecenyl acetate (Z11-14:OAc)] were purchased from
Pherobank (Wageningen, The Netherlands). The isomeric purity of each compound
was >99.5%. All compounds were diluted in redistilled hexane.
Electron microscopy
For scanning electron microscopy, excised antennae from male O.
furnacalis were fixed in 70% ethanol, dehydrated and air-dried. The
antennae were mounted on holders with double-sided tape and coated with
gold:palladium (3:1) in an ion sputter (Polaron SC-7640; Quorum, Newhaven,
UK). The specimens were studied in a scanning electron microscope (LEO 435VP;
Cambridge, UK) with a secondary electron detector at a high voltage of 10 kV.
For transmission electron microscopy, excised antennae were cut into pieces
and immersed in a mixture of 3% paraformaldehyde and 2% glutaraldehyde in 0.1
mol l-1 phosphate buffer, pH 7.2. The specimens were vacuum-pumped
six times for 5 min and left for 8 h at room temperature with gentle shaking
and were washed with buffer and postfixed with 1% osmium tetroxide for 2 h.
After dehydration with dimethoxypropane and acetone, the specimens were
embedded in Spurr's resin and polymerized. Ultrathin sections were cut with a
diamond knife and counterstained with uranyl acetate and lead citrate (2168
Ultrostainer; LKB, Bromma, Sweden). The sections were observed in a JEM-1010
(JEOL, Tokyo, Japan) transmission electron microscope at 60 kV.
Electrophysiology
Single-unit recordings were performed using a tip-cutting technique
(Kaissling, 1974;
Van der Pers and Den Otter,
1978). The moth was restrained in holders cut from plastic pipette
tips, and the head and antennae were fixed with dental wax. A sensillum on the
antenna was cut by microscopic glass knives, and a recording glass electrode
filled with Beadle-Ephrussi Ringer (128 mmol l-1 NaCl, 4.69 mmol
l-1 KCl and 1.97 mmol l-1 CaCl2) was placed
in contact with the cut surface of the sensillum. A grounded reference silver
electrode was inserted into the abdomen. A binocular microscope with up to
300x magnification and two Leica micromanipulators (Wetzlar, Germany)
were used to position the moths, the recording electrode and the glass knife.
The antenna was continuously flushed with a charcoal-filtered and moisturized
air stream through a glass tube (8 mm i.d.) at a speed of 0.5 m
s-1. The outlet of the tube was 10 mm from the antenna. The
stimulus was injected into the air stream in the glass tube 150 mm upstream of
the antenna. The stimulus was delivered in a 2.5 ml air puff for 0.5 s by a
stimulus controller (SFC-1/b; Syntech, Hilversum, The Netherlands). Stimulus
sources consisted of Pasteur pipettes containing 8x15-mm pieces of
filter paper onto which each synthetic compound diluted in 10 µl hexane was
applied. The stimulus pipettes were stored at -20°C when they were not in
use and were renewed every third day.
In screening tests, a blank cartridge plus pipettes loaded with 10 µg of
E12-, Z12- and Z9-14:OAc were tested. Stimuli were tested in random order and
were applied with a 30 s interstimulus interval. If the quality of the contact
was still acceptable, dose-response tests and/or cross-adaptation tests were
performed. In the dose-response tests, 102-105 ng of
each compound were tested in decadic steps, starting with lowest doses.
Cross-adaptation experiments were performed to determine whether neural
activity could be attributed to the same neuron or to different neurons that
produced similar-sized spikes (Kaissling
et al., 1989; Kalinová
et al., 2001). Using a Syntech SFC-2 stimulus controller with dual
channels and single-unit recording as described above, a sensillum was
stimulated twice for 0.5 s at 10 µg dosages with an interval of 0.2 s. For
sensilla containing both large- and small-spiking neurons responding to E12-
and Z12-14:OAc, the following stimulus pairs were tested: (1)
E12-14:OAc/E12-14:OAc, (2) Z12-14:OAc/Z12-14:OAc, (3) E12-14:OAc/Z12-14:OAc
and (4) Z12-14:OAc/E12-14:OAc. At the end of screening, dose-response and
cross-adaptation tests, the antenna was stimulated with 10 µg of either
E12-14:OAc or Z12-14:OAc to verify the initial neural activity. Data from
sensilla containing neurons that failed to respond in a repeatable way at this
stage were excluded from analysis.
The signal was amplified using a custom-built highimpedance amplifier with a low-pass/high-pass filter. During experiments, neural responses were visualized on an oscilloscope. The signal from the amplifiers was fed into a Syntech IDAC A/D converter and transferred to a Compaq ProLinea 4/66 computer (Houston, TX, USA) for analysis with the software program Syntech Auto Spike v. 3.0. The separation of individual neurons was based on differences in the amplitude of their action potentials. The response to a test compound was calculated as the number of spikes during the 0.5 s after stimulation minus the number of spikes during the 0.5 s before stimulation.
Field trapping
Field-trapping experiments were performed at Tanashi (35.7°N,
139.5°E), Tokyo, Japan by methods described in Huang et al.
(Huang et al., 1998a). Test
chemicals were dissolved in hexane at a dosage of 100 µg and loaded on
rubber septa (Aldrich Chemical Co., Milwaukee, WI, USA). Traps (Nitolure;
Nitto Denko, Osaka, Japan) were hung 50 cm above the ground in an experimental
block and were set 10 m apart from each other. The distance between blocks was
more than 50 m. In the first series of experiments, the number of moths
captured by traps baited with different blends of E12- and Z12-14:OAc during
19-29 May 1997 was compared at four experimental blocks. In the second series
of experiments, a reference bait with the blend of 36% E12-14:OAc was compared
with another bait with the same blend plus 1% Z9-14:OAc during 28 August-4
September 1997 in three experimental blocks.
|
Results |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
;
Hallberg et al., 1994;
Hansson et al., 1995).
|
80% of total
sensilla). The trichoid sensilla were 30-60 µm long, with a basal diameter
of 3.0 µm. The wall thickness was 0.5 µm. No obvious variation
in length was found between 12 sensilla situated medially (46.4-58.7 µm)
and 12 situated laterally (41.9-58.7 µm)
(Fig. 1A). At the base, s.
trichodea were surrounded by a honeycomb-like surface and lacked wall pores.
Unbranched dendritic outer segments were observed in this region
(Fig. 1B). In the middle of the
sensillum, pores penetrated the sensillum wall into the sensillum lymph.
Branched and unbranched dendritic outer segments were observed at this height
(Fig. 1C). Out of 59 trichoid
sensilla observed on two male antennae, 57 were innervated by three sensory
cells and two were innervated by two sensory cells.
Sensilla basiconica (Fig.
1A), the second most common sensillum type (15%), had a
shorter length (25 µm), thinner wall with more numerous wall pores and
profusely branched dendritic outer segments compared with s. trichodea.
Chaetic, auricillic, styloconic and coeloconic sensilla were much less
numerous compared with trichoid and basiconic sensilla
(Fig. 1A). S. chaetica were
hairlike and short with a distinct basal socket. Styloconic sensilla were
located at the distal edge of the flagellomeres. Auricillic sensilla were
similar in length to basiconic sensilla but were flattened. Coeloconic
sensilla were of different external morphology with cuticular spines
surrounding a sensory hair. These sensillum types all adhere to morphologies
reported in other moth species (for a review, see
Hansson, 1995).
Electrophysiology
The quality of electrophysiological contacts was tested by stimulation of
long trichoid sensilla on the ventral surface of the middle and basal antenna
with the two pheromone components. In 105 contacted sensilla from 39 males, we
obtained 71 recordings that lasted long enough for physiological
characterization of the response to E12- and Z12-14:OAc (Figs
2,
3). In 47 recordings, a full
characterization of the response to Z9-, E11- and Z11-14:OAc, in addition to
E12- and Z12-14:OAc, was performed (Fig.
4; Table 1).
Recordings typically revealed activity of two or three sensory neurons based
on differences in action potentials with small, medium and large spike
amplitudes. In 71 sensilla recorded, 67 had no background firing, whereas four
sensilla had relatively low background firing prior to stimulation (mean
number of spikes per 0.5 s: 1.75). Blank stimuli (hexane control) elicited no
or very few spikes above background firing.
|
|
|
|
Responses to pheromone components (Types 1-4)
In sensillum type 1 (28% of the tested sensillum population), a neuron
characterized by a large spike amplitude always responded to both pheromone
components in an identical (Mann-Whitney U-test, P>0.05),
dose-dependent fashion (Fig.
3). A small spike amplitude neuron also responded to both
pheromone compounds but with a significantly higher affinity to E12-14:OAc.
The response to E12-14:OAc was dose-dependent, whereas responses elicited by
Z12-14:OAc were not.
|
In sensillum type 3 (31% of the tested sensillum population) a large spiking neuron again responded identically to type 1 and 2. No other responses to pheromone stimulation were registered, and no activity of a small spiking neuron was registered (Fig. 3).
In sensillum type 4 (3% of the tested sensillum population) the large spiking neuron responded exclusively to Z12-14:OAc at the 10 µg dosage. When the dosage was elevated to 100 µg, a weak response was also elicited by the E isomer. The small spiking neuron did not respond to any of the pheromone components at the 10 µg dosage but did respond to the E isomer at the 100 µg level (Fig. 3).
Responses to interspecific signals (subtypes A-D)
In three of the four pheromone-responding sensillum types (1-3), four
subtypes (A-D) could be recognized depending on the response of associated
neurons to the interspecific signals tested; Z9-, E11- and Z11-14:OAc
(Fig. 4;
Table 1). Type 4 sensilla
occurred only as one subtype.
In subtype A (26%) the large spiking neuron excited by the pheromone components was also stimulated by E11- and Z11-14:OAc. The responses to Z9-, E11- and Z11-14:OAc were significantly different at the 100 µg level (Freidman test; P<0.05) but were all dose dependent. This sensillum type also housed a medium spiking neuron responding to stimulation by all the interspecific stimuli tested. No significant differences were found in responses to Z9-, E11- and Z11-14:OAc in the medium spiking neuron (P>0.1).
In subtype B (23%) the large spiking neuron did not respond to any of the interspecific signals. The medium spiking neuron response to all the interspecific signals was identical to that in subtype A.
In subtype C (30%) the large spiking neurons were again non-responsive to interspecific signals. The medium spiking neuron responded to Z9-14:OAc exclusively in a dose-dependent manner.
In subtype D (21%) no response was recorded after stimulation with interspecific signals.
Cross-adaptation tests
As some neurons were found to respond to E12- and Z12-14:OAc (Figs
2,
3), cross-adaptation tests of
large and small spiking neurons housed in sensillum type 1 (N=5) were
performed to clarify whether one or two neurons were present within each spike
class (Fig. 5). Among the large
spiking neurons, pre-exposure and subsequent stimulation with the same
compound resulted in a significantly reduced response. In addition, crosswise
adaptation resulted in the same phenomenon. This strongly indicates that the
same neuron was excited by both pheromone components. Cross-adaptation tests
of large spiking neurons in sensillum type 3 (N=3) produced the same
results (data not shown).
Similarly, small spiking neurons of sensillum type 1 were adapted when stimulated by homologous pairs, although their responses to stimulation by Z12-14:OAc were weak (Fig. 5). In crosswise adaptation using E12- and Z12-14:OAc, the neurons showed a similar pattern as elicited by the same compound combination. However, these neurons did respond to E12-14:OAc after exposure to Z12-14:OAc, a response similar to the first response to E12-14:OAc in the E12-14:OAc/Z12-14:OAc adaptation sequence. This response pattern could be expected, as the response to the E isomer was significantly higher in this neuron, as shown in the dose-response curve in Fig. 3B. Large and small spiking neurons had no background firing prior to stimulation and no response to blank stimuli.
Topographical location of physiological types
No topographical difference in distribution was found among the sensillum
types 1-4. However, the different subtypes described above were found more or
less frequently, depending on the topographical location of the sensillum on
the antenna. Among medial sensilla, subtypes A and B were frequently found,
whereas subtype C was common among lateral sensilla
(Table 1). The frequencies of
subtypes A (1 and 11 for lateral and medial sensilla, respectively), B (2 and
9), C (15 and 1) and D (2 and 6) differed significantly among lateral and
medial parts [extended Fisher's exact test
(Mehta and Patel, 1983);
P<0.001].
Field-trapping test
In the first series of field-trapping tests, trap catches of O.
furnacalis males with different blends of E12- and Z12-14:OAc were
compared (Fig. 6A). Unbaited
control traps caught no males. In traps baited with a single component,
E12-14:OAc (100% E12-14:OAc) or Z12-14:OAc (0% E12-14:OAc), almost no males
were captured either. In traps baited with 36% E12-14:OAc, the pheromone blend
of O. furnacalis in Japan, the catch was significantly the highest,
whereas traps with 10% and 90% E12-14:OAc caught less but these caught
significantly more males than control traps.
|
|
Discussion |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
;
Liljefors et al., 1987;
Akers and O'Connell, 1991;
Hansson et al., 1995;
Mustaparta, 1997;
Wojtasek et al., 1998;
Kalinová et al., 2001;
Larsson et al., 2002). This
has been demonstrated in the closely related European corn borer, O.
nubilalis (Hansson et al.,
1987; Hansson et al.,
1994; Cossé et al.,
1995).
Adaptation studies further strengthened the result that one and the same
large spiking neuron in sensillum types 1-3 responds to the two principal
pheromone components E12- and Z12-14:OAc equally well (Figs
3,
5). The large spiking neurons
were devoted to co-detection of the two pheromone components in 97% of the
investigated sensilla, whereas the small spiking neurons were in 28% of those.
Still, it is clear from the present and previous studies of field-trapping
experiments that O. furnacalis males respond to the sex pheromone
blend selectively and not at all to the single components E12- and Z12-14:OAc
(Huang et al., 1998a;
Boo and Park, 1998). In
addition, in wind-tunnel studies male Asian corn borers respond selectively to
the correct pheromone blend (Zhou and Du,
1999). This means that the male Asian corn borer is indeed able to
determine both the presence of each of the components and their specific ratio
in relation to each other.
What then is the rationale behind this unusual system? There is a high
premium for sensitivity in the moth pheromone detection system, i.e. to
localize the female over long distances
(Hansson et al., 1995). By
using receptor neurons tuned to both pheromone components the male doubles the
number of detecting units, as compared with when each neuron is specifically
tuned to a single component. In this way, the sensitivity of the system should
be higher than in the European corn borer, for example. However, the Asian
corn borer male loses specificity. To solve the specificity problem, the
system contains two crucial neuron types: small spike neuron in type 2 (2S)
and large spike neuron in type 4 (4L). The 2S neuron responds specifically to
the E isomer and the 4L to the Z isomer. These two neurons must thus be
responsible for isomeric discrimination and ratiometric coding. The 2S neuron
was present in 38% of the sensilla investigated, whereas the 4L was found in
only 3%. To further strengthen E isomer identification, the small spike neuron
in Type 1 shows a differential response to the components, with a
significantly stronger response to the E isomer. The detection of E isomer
thus seems to be robust, but is 3% of the sensillum population enough to allow
reliable detection of the Z isomer and ratiometric coding? From earlier
investigations we know that it is indeed sufficient, with a very low
percentage of neurons detecting behaviorally crucial odors
(Kalinová et al., 2001;
Baker et al., 2004). In the
turnip moth, Agrotis segetum, approximately 1-2% of the male
olfactory receptor neurons are tuned to an important pheromone component, and
in this case no other neurons respond to this specific component
(Löfstedt et al., 1982;
Hansson et al., 1990).
The pheromone detection system of O. furnacalis can thus be
divided into two parts: one `sensitivity' part formed by the non-specific
pheromone-detecting neurons and one `specificity' part formed by the two
neuron types responding differentially to the two isomers. It thus seems as
though evolution has `allowed' the development of a specific part of the
system towards less sensitivity. This could be the result of the unusual
pheromone composition of O. furnacalis. No other species of insects
are known to use E12- and/or Z12-14:OAc
(Witzgall et al., 2004). Could
it thus be the case that the specificity demands are less restrictive in a
detection system when the signals are highly specific and not used by any
other species in the communication channel? A similar case of less restrictive
specificity of pheromone receptor neurons has been reported in Yponomeuta
rorellus, which use another unusual pheromone component, saturated
tetradecyl acetate (Löfstedt et al.,
1990).
Z9-, E11- and Z11-14:OAc are not included in sex pheromone gland extracts
of O. furnacalis (Ando et al.,
1980) but elicited clear responses in male olfactory receptor
neurons. Similar to the pheromone-detecting neurons, some neurons displayed a
very broad response profile to Z9-, E11- and Z11-14:OAc. Medium spiking
neurons present in sensillum subtypes A and B responded equally well to Z9-,
E11- and Z11-14:OAc. In sensillum subtype C the medium spiking neurons
responded specifically to Z9-14:OAc and had a considerably higher sensitivity
than other neurons responding to this compound.
Our field-trapping experiments showed that Z9-14:OAc works as an antagonist
for behavioral responses toward a conspecific pheromone with E12- and
Z12-14:OAc in O. furnacalis (Fig.
6). This compound also works as a behavioral antagonist in O.
nubilalis and O. scapulalis
(Glover et al., 1989;
Ishikawa et al., 1999a). In
addition, Z9-14:OAc is a sex pheromone component in O. zaguliaevi and
O. zealis (Huang et al.,
1998b; Ishikawa et al.,
1999a). Z9-14:OAc may have played an important role in pre-mating
isolation between Ostrinia species. E11- and Z11-14:OAc, which are
also pheromone components of closely related Ostrinia species
(Huang et al., 1997;
Ishikawa et al., 1999b), may
have played a similar role for O. furnacalis. O. furnacalis and
O. nubilalis have been shown to detect the antagonist Z9-14:OAc by
specifically tuned receptor neurons (present study)
(Hansson et al., 1987;
Cossé et al., 1995).
Several other moth species are known to have neurons responding to pheromone
components of their closely related species as behavioral antagonists,
presumably for pre-mating isolation
(Löfstedt et al., 1991;
Mustaparta, 1997;
Larsson et al., 2002).
When contemplating detection systems for behavioral antagonists the demand
for sensitivity remains the same as for pheromone detection. The reasoning
regarding specificity can, however, be more or less the opposite. One
unspecific neuron, tuned to all antagonists, can serve as a general antagonist
detector. The only message that needs to be conveyed is to abort flight
towards the source, irrespective of which antagonist is present. The
antagonist neurons in subtypes A and B
(Fig. 4) thus make perfect
sense in being non-specific. The neuron in subtype C specific to Z9-14:OAc
shows higher sensitivity than the neuron to other potential antagonists, but
can this antagonist be more important than the others? In one neuron type, the
large spiking neuron in type 1, subtype A
(Fig. 3;
Table 1), conditions were
further complicated. In the neuron types, both the sex pheromone components,
E12- and Z12-14:OAc, and the potential antagonists, E11- and Z11-14:OAc, were
stimulating. This neuron thus seems to transcend the absolute border in
specificity; between attractant and their antagonists. A similar function,
with a neuron responding to both pheromone components and antagonists, has
been indicated in Yponomeuta rorellus
(Löfstedt et al.,
1990).
O. furnacalis has a peculiar coding system for its two major
pheromone components, whereas the close relative O. nubilalis has
specialized neurons tuned to each pheromone component, as reported in many
other moth species (Hansson et al.,
1987; Akers and O'Connell,
1991; Mustaparta,
1997; Kalinová et al.,
2001; Larsson et al.,
2002). In rare cases, males of O. nubilalis show
behavioral response to E12- and Z12-14:OAc
(Roelofs et al., 2002;
Linn et al., 2003), suggesting
that their neurons can sometimes respond to the compounds of O.
furnacalis. In addition, O. furnacalis has neurons responding to
E11- and Z11-14:OAc. It thus seems that pheromone-detecting neurons of
Ostrinia species can inherently respond to isomers of 11- and
12-14:OAc, but the response specificity to the compounds differs dramatically
among the species. The Ostrinia species complex thus offers an
excellent system for future studies of the evolution of pheromone
communication systems, both at the sender and receiver levels.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
Present address: Max Planck Institute for Chemical Ecology, Department of
Evolutionary Neuroethology, Hans-Knoell-Strasse 8, D-07745 Jena, Germany 
|
References |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Akers, R. P. and O'Connell, R. J. (1991). Response specificity of male olfactory receptor neurons for the major and minor components of a female pheromone blend. Physiol. Entomol. 16,1 -17.
Ando, T., Saito, O., Arai, K. and Takahashi, N. (1980). (Z)- and (E)-12-tetradecenyl acetates: sex pheromone components of oriental corn borer (Lepidoptera: Pyralidae). Agric. Biol. Chem. 44,2643 -2649.
Anton, S., Löfstedt, C. and Hansson, B. S. (1997). Central nervous processing of sex pheromones in two strains of the European corn borer Ostrinia nubilalis (Lepidoptera: Pyralidae). J. Exp. Biol. 200,1073 -1087.[Abstract]
Baker, T. C., Ochieng', S. A., Cossé, A. A., Lee, S. G., Todd, J. L., Quero, C. and Vickers, N. J. (2004). A comparison of responses from olfactory receptor neurons of Heliothis subflexa and H. virscens to components of their sex pheromone. J. Comp. Physiol. A 190,155 -165.[CrossRef][Medline]
Boo, K. S. and Park, J. W. (1998). Sex pheromone composition of the Asian corn borer moth, Ostrinia furnacalis (Guenée) (Lepidoptera: Pyralidae) in South Korea. J. Asia Pac. Entomol. 1,77 -84.
Cossé, A. A., Campbell, M. G., Glover, T. J., Linn, C. E., Jr, Todd, J. L., Baker, T. C. and Roelofs, W. L. (1995). Pheromone behavioral responses in unusual male European corn borer hybrid progeny not correlated to electrophysiological phenotypes of their pheromone-specific antennal neurons. Experientia 51,809 -816.[CrossRef]
Glover, T. J., Tang, X.-H. and Roelofs, W. L. (1987). Sex pheromone blend discrimination by male moths from E and Z strains of European corn borer. J. Chem. Ecol. 13,143 -151.
Glover, T. J., Perez, N. and Roelofs, W. L. (1989). Comparative analysis of sex-pheromone-response antagonists in three races of European corn borer. J. Chem. Ecol. 15,863 -873.[CrossRef]
Hallberg, E., Hansson, B. S. and Steinbrecht, R. A. (1994). Morphological characteristics of antennal sensilla in the European corn borer Ostrinia nubilalis (Lepidoptera: Pyralidae). Tissue Cell 26,489 -502.[CrossRef]
Hansson, B. S. (1995). Olfaction in Lepidoptera. Experientia 51,1003 -1027.[CrossRef]
Hansson, B. S., Löfstedt, C. and Roelofs, W. L. (1987). Inheritance of olfactory response to sex pheromone components in Ostrinia nubilalis. Naturwissenschaften 74,497 -499.[CrossRef]
Hansson, B. S., Tóth, M., Löfstedt, C., Szöcs, G., Subchev, M. and Löfqvist, J. (1990). Pheromone variation among eastern European and a western Asian population of the turnip moth, Agrotis segetum. J. Chem. Ecol. 16,1611 -1622.[CrossRef]
Hansson, B. S., Hallberg, E., Löfstedt, C. and Steinbrecht, R. A. (1994). Correlation between dendrite diameter and action potential amplitude in sex pheromone specific receptor neurons in male Ostrinia nubilalis (Lepidoptera: Pyralidae). Tissue Cell 26,503 -512.[CrossRef]
Hansson, B. S., Blackwell, A., Hallberg, E. and Löfqvist, J. (1995). Physiological and morphological characteristics of the sex pheromone detecting system in male corn stemborers, Chilo partellus (Lepidoptera: Pyralidae). J. Insect Physiol. 41,171 -178.[CrossRef]
Huang, Y., Tatsuki, S., Kim, C. G., Hoshizaki, S., Yoshiyasu, Y., Honda, H. and Ishikawa, Y. (1997). Identification of sex pheromone of Adzuki bean borer, Ostrinia scapulalis. J. Chem. Ecol. 23,2791 -2802.
Huang, Y., Takanashi, T., Hoshizaki, S., Tatsuki, S., Honda, H., Yoshiyasu, Y. and Ishikawa, Y. (1998a). Geographic variation in sex pheromone of Asian corn borer, Ostrinia furnacalis, in Japan. J. Chem. Ecol. 24,2079 -2088.[CrossRef]
Huang, Y., Honda, H., Yoshiyasu, Y., Hoshizaki, S., Tatsuki, S. and Ishikawa, Y. (1998b). Sex pheromone of the butterbur borer, Ostrinia zaguliaevi. Entomol. Exp. Appl. 89,281 -287.[CrossRef]
Ishikawa, Y., Takanashi, T. and Huang, Y. (1999a). Comparative studies on the sex pheromones of Ostrinia spp. in Japan: the burdock borer, Ostrinia zealis.Chemoecology 9,25 -32.
Ishikawa, Y., Takanashi, T., Kim, C. G., Hoshizaki, S., Tatsuki, S. and Huang, Y. (1999b). Ostrinia spp. in Japan: their host plants and sex pheromones. Entomol. Exp. Appl. 91,237 -244.[CrossRef]
Kaissling, K. E. (1974). Sensory transduction in insect olfactory receptors. In Biochemistry of Sensory Functions (ed. L. Jaenicke), pp.243 -273. Berlin: Springer.
Kaissling, K. E., Hildebrand, J. G. and Tumlinson, J. H. (1989). Pheromone receptor cells in the male moth Manduca sexta. Arch. Insect Biochem. Physiol. 10,273 -279.[CrossRef]
Kalinová, B., Hoskovec, M., Liblikas, I., Unelius, C. R.
and Hansson, B. S. (2001). Detection of sex pheromone
components in Manduca sexta (L.). Chem.
Senses 26,1175
-1186.
Klun, J. A., Anglade, P. L., Baca, F., Chapman, O. L., Chiang, H. C., Danielson, D. M., Farber, W., Fels, P., Hill, R. E., Hudon, M., et al. (1975). Insect sex pheromones: intraspecific pheromonal variability of Ostrinia nubilalis in North America and Europe. Environ. Entomol. 4,891 -894.
Klun, J. A., Bierl-Leonhardt, B. A., Schwarz, M., Litsinger, J. A., Barrion, A. T., Ciang, H. C. and Jiang, Z. (1980). Sex pheromone of the Asian corn borer moth. Life Sci. 27,1603 -1606.[CrossRef][Medline]
Kou, R., Ho, H. Y., Yang, H. T., Chow, Y. S. and Wu, H. J. (1992). Investigation of sex pheromone of female Asian corn borer, Ostrinia furnacalis (Hübner) (Lepidoptera: Pyralidae) in Taiwan. J. Chem. Ecol. 18,833 -840.[CrossRef]
Larsson, M. C., Hallberg, E., Kozlov, M. V., Francke, W.,
Hansson, B. S. and Löfstedt, C. (2002). Specialized
olfactory receptor neurons mediating intra- and interspecific chemical
communication in leafminer moths Eriocrania spp. (Lepidoptera:
Eriocraniidae). J. Exp. Biol.
205,989
-998.
Liljefors, T., Bengtsson, M. and Hansson, B. S. (1987). Effects of double-bond configuration on interaction between a moth sex pheromone component and its receptor: a receptor-interaction model based on molecular mechanics. J. Chem. Ecol. 13,2023 -2040.[CrossRef]
Linn, C., Jr, O'Connor, M. and Roelofs, W. L. (2003). Silent genes and rare males: a fresh look at pheromone blend response specificity in the European corn borer moth, Ostrinia nubilalis. J. Insect Sci. 3,15 .[Medline]
Löfstedt, C. and Hansson, B. S. (1989). Pheromone detection in moths: peripheral discrimination and its genetic control. In Proceedings of the Second International Congress of Neuroethology (ed. J. Erber, R. Menzel, H.-J. Pflüger and D. Todt), pp. 245-246. Stuttgart-New York: Georg Thieme Verlag.
Löfstedt, C., Van der Pers, J. N. C., Löfqvist, J., Lanne, B. S., Appelgren, M., Bengström, G. and Thelin, B. (1982). Sex pheromone components of the turnip moth, Agrotis segetum: chemical identification, electrophysiological evaluation and behavioral activity. J. Chem. Ecol. 8,1305 -1321.[CrossRef]
Löfstedt, C., Hansson, B. S., Dijkerman, H. and Herrebout, W. M. (1990). Behavioural and electrophysiological activity of unsaturated analogues of the pheromone tetradecyl acetate in the small ermine moth Yponomeuta rorellus. Physiol. Entomol. 15, 47-54.
Löfstedt, C., Herrebout, W. M. and Menken, S. B. J. (1991). Sex pheromones and their potential role in the evolution of reproductive isolation in small ermine moths (Yponomeutidae). Chemoecology 2,20 -28.
Mani, E., Riggenbach, W. and Mendik, M. (1978). Zucht des Apfelwicklers Lasperyesia pomonella (L.) auf künstlichem Nährboden, 1968-78. Mitt. Schweiz. Entomol. Ges. 51,315 -326.
Mehta, C. R. and Patel, N. R. (1983). A network algorithm for performing Fisher's exact test in r x c contingency tables. J. Am. Stat. Assoc. 78,427 -434.[CrossRef]
Mustaparta, H. (1997). Olfactory coding mechanisms for pheromone and interspecific signal information in related moth species. In Insect Pheromone Research: New Directions (ed. R. T. Cardé and A. K. Minks), pp.144 -163. New York: Chapman & Hall.
Ren, Z. L., Zhang, Q. M. and Guo, S. H. (1987). Scanning electron microscopy of the antennae of Asian corn borer, Ostrinia furnacalis. Acta Entomol. Sin. 30, 26-30. [In Chinese with English abstract].
Roelofs, W. L., Liu, W., Hao, G., Jiao, H., Rooney, A. P. and
Linn, C. E., Jr (2002). Evolution of moth sex pheromones via
ancestral genes. Proc. Natl. Acad. Sci. USA
99,13621
-13626.
Todd, J. L. and Baker, T. C. (1999). Function of peripheral olfactory organs. In Insect Olfaction (ed. B. S. Hansson), pp. 67-97. Berlin: Springer.
Van der Pers, J. N. C. and Den Otter, C. J. (1978). Single cell responses from olfactory receptors of small ermine moths to sex-attractants. J. Insect Physiol. 24,337 -343.[CrossRef]
Witzgall, P., Lindblom, T., Bengtsson, M. and Tóth, M. (2004). The Pherolist. www-pherolist.slu.se
Wojtasek, H., Hansson, B. S. and Leal, W. S. (1998). Attracted or repelled? - a matter of two neurons, one pheromone binding protein, and a chiral center. Biochem. Biophys. Res. Commun. 250,217 -222.[CrossRef][Medline]
Zhou, H. and Du, J. (1999). Behaviour effect of various binary and ternary sex pheromone blends on the Asian corn borer moths (Ostrinia furnacalis). Entomol. Sin. 6, 156-165.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
