Disruption_of_responses_to_pheromone

1. Disruption of responses to pheromone by
(Z)-11-hexadecenyl trifluoromethyl ketone, an
analogue of the pheromone, in the cabbage
armyworm Mamestra brassicae
Michel Renou,1
* Andrée Berthier1
and Angel Guerrero2
1
INRA UR258, Phytopharmacie et Médiateurs Chimiques, Route de Saint Cyr, 78026 Versailles, France
2
Department of Biological Organic Chemistry, IIQAB, (CSIC), Jordi Girona 18-26, 08304 Barcelona, Spain
Abstract: The effects of (Z)-11-hexadecenyl trifluoromethyl ketone (Z11-16:TFMK) a fluorinated
pheromone analogue, on the responses to sex pheromone of the male cabbage armyworm, Mamestra
brassicae, have been investigated in an actograph and by electroantennography (EAG). In spite of its
structural proximity with the natural pheromone, Z11-16:TFMK was poorly active in EAG, and not
active on male behaviour. When permeated in the air, Z11-16:TFMK reversibly inhibited the electro-
antennographic responses to (Z)-11-hexadecenyl acetate (Z11-16:Ac), the main component of the sex
pheromone. In the actograph, the latency of the activation was increased and the intensity of the
behavioural activity of males in response to Z11-16:Ac was significantly reduced in the presence of
Z11-16:TFMK. These results, along with others previously reported by us, provide new pointers to the
possible use of Z11-16:TFMK in pest-control strategies.
# 2002 Society of Chemical Industry
Keywords: pheromone; trifluoromethyl ketone; inhibition; cabbage armyworm; Mamestra brassicae
1 INTRODUCTION
Chemical communication plays a pre-eminent role in
insect reproduction. This is especially so in the case of
moths, where mate finding and mate recognition rely
on volatile sex pheromones. Males respond to the
specific blends emitted by females, and orient very
precisely to pheromone sources. The components of
the blends are detected by selective and sensitive
receptors in the male antennae. Electrophysiological,
ethological and molecular approaches have contri-
buted to a better understanding of the mechanisms
underlying the remarkable capacities of the insect
chemoreceptor system.
In this context, olfaction inhibitors are invaluable
pharmacological tools to study olfaction mechanisms
and, in practice, they can be considered potential
agents in pest-control studies.1
Among other candi-
dates, and due to the presence in the insect antenna of
esterases specifically involved in the catabolism of
pheromone compounds, a class of esterase inhibitors,
the trifluoromethyl ketones,2–5
has been the subject of
great interest. Specific applications of the latter
substances to the inhibition of the insect olfaction
process have been reported.6,7
Thus, pheromone
analogues bearing a trifluoromethyl ketone function
have been synthesized8,9
and their biological activity
evaluated.9–11
In this regard, Bau et al12
demonstrated
for the first time that several TFMK analogues
topically applied to the antennae disrupt the upwind
flight of males to pheromone sources in a wind tunnel
in two moth species, the Egyptian armyworm,
Spodoptera littoralis Boisd, and the Mediterranean corn
borer, Sesamia nonagrioides Lef (Sesamia calamistis
Hamps). However, in these experiments the fluori-
nated analogues were deposited directly on the male
antennae before the behavioural tests, an unnatural
mode of application that does not take advantage of
their volatility, and consequently could introduce
some artefacts. In further experiments, addition of
(Z)-11-hexadecenyl trifluoromethyl ketone (Z11-16:
TFMK) to the attractive pheromone blend resulted in
erratic flights of male S nonagrioides in the wind
tunnel.13
This compound also exerted its antagonistic
effect on male orientation when Z11-16:TFMK and
the sex attractant were released from two sources
separated by 5cm from each other. In the field,
captures of male S nonagrioides decreased when
Z11-16:TFMK or other TFMKs were added to the
pheromone blend in the dispenser.13
During experi-
ments conducted in infested maize fields in Spain,
sticky traps baited with a 10:1 mixture of Z11-16:
TFMK and the pheromone blend caught only 10% of
the number of males attracted to traps baited with the
pheromone blend.13
(Received 22 February 2002; accepted 15 April 2002)
* Correspondence to: Michel Renou, INRA UR258, Phytopharmacie et Médiateurs Chimiques, Route de Saint Cyr, 78026 Versailles, France
E-mail: renou@versailles.inra.fr
Contract/grant sponsor: CICYT; contract/grant number: AGL2000-1695-C02-01
# 2002 Society of Chemical Industry. Pest Manag Sci 1526–498X/2002/$30.00 839
Pest Management Science Pest Manag Sci 58:839–844 (online: 2002)
DOI: 10.1002/ps.534

2. In this paper we report on the activity of Z11-16:
TFMK on the behaviour of males of the cabbage
armyworm, Mamestra brassicae (L). The sex phero-
mone blends of M brassicae and of S nonagrioides share
the same main component, (Z)-11-hexadecenyl
acetate (Z11-16:Ac). The pheromone receptor system
of M brassicae has been well characterized.14
Males
respond to Z11-16:Ac by wing fanning and intense
locomotion.15
Thus, this species was a suitable model
to investigate further the effects of a fluorinated
pheromone derivative on the behavioural response of
male moths to pheromone when diffused in the air.
Male behaviour was recorded in response to Z11-16:
TFMK alone, to Z11-16:Ac in pure air or in air loaded
with Z11-16:TFMK, and to blends of the TFMK with
Z11-16:Ac. To measure the behavioural responses of
males, an actograph was used, as it enabled quantifica-
tion of the response of single insects. Correlation of
behavioural and sensory effects was also done by using
electroantennography to measure the effect of Z11-16:
TFMK on the responses of olfactory receptors to
Z11-16:Ac.
2 MATERIALS AND METHODS
2.1 Insects
Mamestra brassicae were reared in the laboratory on an
artificial medium modified after Poitout and Bues.16
Male and female pupae were sorted and kept
separately. Adult male moths were provided with a
10% sucrose solution, and conditioned to a 16:8h
light:dark photoperiod. Behavioural tests were per-
formed on 3- to 5-day-old males during the last 3h of
the scotophase. Each male moth was used only once.
2.2 Compounds
Z11-16:TFMK was synthesized as previously re-
ported.8
Z11-16:Ac, free from the corresponding
alcohol, was prepared in the laboratory and purified
by HPLC. Both compounds were diluted in hexane to
achieve the appropriate concentrations.
2.3 Bioassays
Bioassays were carried out using an actograph already
described15
and consisting of a glass olfactometer and
a radar detector. Briefly, the olfactometer consisted of
a cylindrical observation chamber (120mm length
30mm ID), with an upwind air inlet of smaller
diameter (6mm ID) that was connected to a perma-
nent source of charcoal-filtered air (85 litre h 1
). For
olfactory stimulation, a lateral branch, perpendicular
to the main branch, was used to introduce a Pasteur
pipette containing a piece of filter paper loaded with
the stimulus. Stimulation was achieved by applying an
air puff (3s, 21ml) through the Pasteur pipette. Air
from the observation chamber was evacuated out of
the room by an exhaust fan. After each test the
observation chamber was washed overnight in a 5%
solution of Decon (Prolabo, Paris), rinsed in distilled
water, and dried at 110°C.
Movements of the insect were monitored by a
Doppler radar sensor (Alpha Industries, type
GOS2780). The sensor had a working frequency of
24GHz and an output power of 3mW. The output
signal from the radar sensor was high-pass filtered,
amplified 10, and fed into the 16 bits acquisition
board IDAC-02 (Syntech, Hilversum) of a PC. Data
acquisition was performed at 500 samples s 1
during
15min. The insect movements were continuously
recorded during a 60-s pre-stimulation period and
during a 600-s post-stimulation period. When neces-
sary, visual observations of behaviour completed the
activity records. The software GC-EAD for Windows
(Syntech, Hilversum) was used to edit the recordings
and measure the amplitude and temporal parameters
of the response.
Experiments were run at 25°C. Red light (0.3 lx)
was provided by a 60-W incandescent lamp positioned
above the observation chamber. A single male was
introduced into a clean observation chamber and left
to acclimatize to the experimental room conditions for
1h. To determine the intrinsic activity of Z11-16:
TFMK, responses to 3-s puffs of 0.1 (nine replicates)
or 10mg (14 replicates) of Z11-16:TFMK were com-
pared with responses to 0.1mg of Z11-16:Ac (n=24).
Control insects (n=25) received a puff of the solvent.
Effects of Z11-16:TFMK on responses of male M
brassicae to Z11-16:Ac were investigated, first by
measuring the responses to a puff of Z11-16:Ac in
air loaded with Z11-16:TFMK and, second, by
measuring responses to puffs with blends of Z11-16:
TFMK and Z11-16:Ac. To measure the responses in
Z11-16:TFMK-loaded air, an odour background of
the inhibitor was created in the observation chamber
by introducing a filter paper loaded with the appro-
priate amount (0.1mg, n=22; 1mg, n=26; or 10mg,
n =28) of Z11-16:TFMK into the permanent airflow
carried by the inlet tube. After a minimum exposure
time of the male moth to the background of 180s, a
single puff (3s, 21ml) of air loaded with Z11-16:Ac
(test stimulus, 100ng on the filter paper) was
delivered. To measure the responses in air to 1:10
blends of the pheromone and its analogue, the
appropriate doses of Z11-16:Ac and Z11-16:TFMK
were successively deposited on the same filter paper
that was used as the stimulus source. Males were
challenged with the following two blends of the
pheromone main component and its fluorinated
derivative: 0.01:0.1mg (n =22) and 0.1:1mg (n =21).
Responses to blends were compared to responses to
0.01mg (n =24) or 0.1mg (n =9) of Z11-16:Ac.
Relevant behavioural parameters were determined
after repeated observations of the behaviour of male M
brassicae in the actograph (unpublished data and
Reference 15). After pheromone stimulation, males
became very active, performing wing fanning and
intense locomotion in the observation chamber. Both
activities are typical of male moth precopulatory
behaviour and they were easily detected by the radar
sensor, producing bursts of high amplitude spikes.15
840 Pest Manag Sci 58:839–844 (online: 2002)
M Renou, A Berthier, A Guerrero

3. Males usually maintained a high level of locomotory
activity for several minutes after the stimulation, but
short pauses within a response enabled the discrimina-
tion of individual bursts of activity. Because TFMK
inhibits the catabolism of the pheromone compound,
an effect on response kinetics was expected. Special
attention was paid to the duration of the first burst,
which has been shown to be significantly affected by
the fluorinated compound 3-octylthio-1,1,1-trifluoro-
propan-2-one (OTFP).15
Thus, the following par-
ameters were measured to quantify the behaviour of
males:
– percentage of males responding by intense locomo-
tion or/and wing fanning to Z11-16:Ac within 60s of
stimulus. After preliminary experiments showing
that control insects responded within a few tens of
seconds, the activity of males that initiated their
activity more than 60s after the pheromone puff was
not considered as a positive response but rather as
random activity;
– latency of the insect arousal;
– duration of the first burst of response;
– accumulated time of locomotory and wing-fanning
activity during the 600s of observation;
– activity intensity. Preceding work15
established that
the amplitude of the signal from the radar is
correlated to the intensity of the insect response.
This value was quantified by computing the area
below the signal line.
2.4 Electroantennography
Electroantennograms (EAG) were recorded in living
insects according to standard procedures using glass
micro-electrodes filled with Roeder’ saline.7
A male
moth was anaesthetized with carbon dioxide and
restricted in a Styrofoam block. The reference
electrode was introduced in the unsclerified mem-
brane between head and prothorax. One antenna was
immobilized, the last articles excised, and the tip
inserted into the recording electrode. The EAG signal
was amplified (1000) and filtered (DC to 1kHz).
The EAG recordings were digitised on a PC via a
DASH 16 analogue-to-digital conversion board and
stored on the hard disk. Control of the acquisition
board and analysis of the EAGs were performed by
specific programs developed in Asyst (McMillian
Software Co).
A flow of filtered and re-humidified air (1.5 litre
min 1
) was permanently directed onto the antenna
through the main branch of a glass tube (10mm ID).
Olfactory stimuli were delivered by puffing air (0.5s,
0.5 litre min 1
) through a Pasteur pipette connected to
a lateral branch and containing a filter paper loaded
with the stimulus. Dose-response curves were estab-
lished by measuring EAG responses to increasing
doses of Z11-16:Ac or Z11-16:TFMK in six different
insects. For measuring background effects, Z11-16:
TFMK was applied by turning on a flux of air (0.1 litre
min 1
) through another Pasteur pipette containing a
filter paper loaded with 10mg of the analogue. Three
EAG responses to Z11-16:Ac were measured at 2-min
intervals in pure air to obtain the response level before
treatment. The flux of TFMK was then turned on, and
three other EAG responses were measured (during
treatment). After 15min the flux was turned off and
three new stimulations were performed with Z11-16:
Ac (after treatment). The experiment was repeated on
seven different insects.
2.5 Statistics
Behavioural data were analyzed either by chi-squared
tests for the number of responses, or through a general
linear model for duration and amplitude of responses.
Wilcoxon matched-pairs signed ranks tests were used
for EAG data.
3 RESULTS
3.1 Intrinsic activity of Z11-16:TFMK
3.1.1 Electrophysiology
The EAG dose-response curves (Fig 1) show that
Z11-16:TFMK was significantly less active than
Z11-16:Ac. Only the highest doses of Z11-16:TFMK
(1, 10 and 100mg) produced EAG responses signi-
ficantly different from control stimulus (P 0.05,
Wilcoxon).
3.1.2 Behaviour
In the absence of olfactory stimulus, the level of male
activity was low. Only 16% of males showed some
activity within 60s after a control puff (Table 1).
Latency for activation was 354.1 (237.7)s and the
cumulative time of activity 106.2 (122.6)s in control
insects. After a single 3-s puff of Z11-16:TFMK at
0.1mg the percentage of males active within 60s, the
latency and the cumulative activity time were not
significantly different from the control. A higher dose
of the inhibitor (10mg) had no effect on the number of
active males (28.6%) and the time of activity (164.6
(130.1)s), although there was some decrease (203.6
(201.9)s) in the latency, but this was non-significant.
For comparison, Z11-16:Ac, the main pheromone
Figure 1. Comparison of the EAG activity of Z11-16:Ac and Z11-16:TFMK.
Increasing doses of both compounds were tested on the antennae of male
Mamestra brassicae. Means of six replicates; error bars are standard
deviations.
Pest Manag Sci 58:839–844 (online: 2002) 841
Disruption of responses to pheromone by an analogue in M brassicae

4. component, induced activity in 78.6% of males with
an early (latency 53.3(126.9)s) and long-lasting
response (264.7(141.5)s).
3.2 Effects of a background of Z11-16:TFMK
3.2.1 Electrophysiology
Applied as a background, Z11-16:TFMK reduced the
amplitude of the EAG responses to Z11-16:Ac (Fig 2),
and significantly increased its repolarization time.
Both effects were fully reversible. The 4/5 depolariza-
tion time during the treatment (94.5(32.1)s) was
not significantly different from its value before the
treatment (88.9(36.8)s; Wilcoxon matched-pairs
signed ranks test; data not shown).
3.2.2 Behaviour
Effects of permanent stimulation with Z11-16:TFMK
on responses to Z11-16:Ac were tested at three doses
of the fluorinated analogue (Table 2). Male activity
was clearly lower in the presence of the fluorinated
analogue (Fig 3). The number of insects responding to
the pheromone was significantly reduced at 1 and
10mg doses of Z11-16:TFMK, while there was no
effect at 0.1mg (Table 2). The latency of the response
increased with the dose of the chemical, being
significant at the highest dose. The duration of the
Table 1. Behavioural responses of male
Mamestra brassicae to puffs of Z11-16:
TFMKa,b
n
Males active
within 60s (%)
Latency for
activation (s) (SD)
Cumulative activity
time (s) (SD)
Control (solvent) 25 16.0 b 354.1 (237.7) b 106.2 (122.6) b
Z11-16:Ac 0.1mg 24 78.6 a 53.3 (126.9) a 264.7 (141.5) a
Z11-16:TFMK 0.1mg 9 22.2 b 283.4 (215.0) b 116.1 (81.0) b
Z11-16:TFMK 10mg 14 28.6 b 203.6 (201.9) ab 164.6 (130.1) b
a
Activity was recorded in an actograph during 600s after a puff of 3s.
b
Values followed by different letters within the same column are significantly different (chi2
for percentages
of males; general linear model elsewhere, P 0.05).
Figure 2. Effects of Z11-16:TFMK on the amplitude (AMPLI, dashed line)
and the repolarisation time (2/3RT, continuous line) of the EAG response of
Mamestra brassicae male antennae to Z11-16:Ac. Z11-16:TFMK was
released in air from t=13min to t=27min. Data are the ratios of the value at
time=t over the mean values of the EAG in air, before treatment. Means of
seven replicates; error bars are standard deviations.
Table 2. Effects of a background of Z11-16:TFMK on the behavioural responses of male Mamestra brassicae to a 3-s puff of Z11-16:Ac (0.1mg)a
Background n
Responses to
Z11-16:Ac (%)
Latency (s)
(SD)
Cumulative activity
time (s) (SD)
First burst
duration (s) (SD)
Activity intensity
(s) (SD)
Control 24 78.6 a 53.3 (126.9) a 264.7 (141.5) a 95.9 (104.5) NS 4641.8 (2711.6) a
Z11-16:TFMK (0.1mg) 22 86.4 a 82.5 (180.3) a 229.9 (149.7) ab 144.8 (137.0) NS 2969.3 (1965.0) b
Z11-16:TFMK (1mg) 26 61.5 ab 120.9 (199.4) a 144.8 (100.2) bc 67.5 (78.2) NS 2102.8 (1267.1) bc
Z11-16:TFMK (10mg) 28 50.0 b 200.2 (245.1) b 116.9 (114.2) c 51.3 (54.2) NS 1516.7 (1451.0) c
a
Values followed by different letters within the same column are significantly different (general linear model, or chi2
for percentages, P 0.05).
Figure 3. Samples of actographic recordings of the behavioural activity of
male Mamestra brassicae in response to Z11-16:Ac recorded in air, or in air
with Z11-16:TFMK. Lower traces in both recordings indicate the puffs of the
main pheromone component (100ng Z11-16:Ac).
842 Pest Manag Sci 58:839–844 (online: 2002)
M Renou, A Berthier, A Guerrero

5. insect response was decreased. The total time during
which the male was active and the intensity of its
activity were also significantly reduced at 1 and 10mg.
The duration of the first burst of activity seemed
smaller in the presence of the TFMK, but there was a
very high variability among the values and the
difference was not statistically significant (GLM,
P =0.052).
3.3 Responses to blends of Z11-16:Ac and
Z11-16:TFMK
In this experiment, blends of Z11-16:TFMK and
Z11-16:Ac were deposited onto the filter paper and
male behavioural responses to a 3-s puff of the blend
were monitored in the actograph and compared with
responses to a corresponding amount of the major
component of the pheromone. Thus, Z11-16:Ac and
Z11-16:TFMK co-evaporated from the same source
and the exposure of the insect to the fluorinated
compound was brief. In these conditions, latency of
activation was significantly higher in response to the
blend of 10ng of Z11-16:Ac and 100ng of Z11-16:
TFMK, compared with that to Z11-16:Ac alone at the
same dose (Table 3). The other parameters, such as
percentage of males responding, cumulative time of
activity and intensity of response were not altered by
the addition of 0.1 and 1mg of Z11-16:TFMK to 0.01
and 0.1mg of Z11-16:Ac.
4 DISCUSSION AND CONCLUSIONS
The actograph is well suited to monitor sustained
spontaneous activity of insects,17
as well as transient
responses to various stimuli. Other important features
of the radar sensor have been delineated by us.15
Male
M brassicae respond to the main pheromone com-
ponent by wing fanning and intense locomotion.
Intensity and duration of this response to Z11-16:Ac
were significantly reduced when Z11-16:TFMK was
released in the olfactometer chamber during the tests.
Males became active after a longer latency than when
stimulated with the pheromone only, spending less
time responding to the stimulus. Similarly, the beha-
vioural responses of males to the main pheromone
component were smaller in air loaded with Z11-16:
TFMK. Responses to blends containing ten times
more of the fluorinated derivative showed that a brief
exposure to Z11-16:TFMK increased the latency of
the behavioural response, but did not modify sig-
nificantly its level. These results are consistent with
other experiments in which Z11-16:TFMK was
shown to effectively disrupt the orientation flight of
Mediterranean corn borer males, S nonagrioides, to the
synthetic pheromone or to virgin females when the
insects antennae were topically treated with the
inhibitor.12
The fluorinated derivative elicited its
disruptive effect by strongly modifying the orientation
pattern into the plume.
With regard to the question of its mode of action, in
vitro experiments have shown that Z11-16:TFMK
inhibits the hydrolysis of Z11-16:Ac to its alcohol
analogue by the sensillar esterases contained in
antennal extracts. We would expect that this inhibition
of the pheromone catabolism would cause prolonged
response in vivo. However, behavioural responses of
males were shorter, thus implying another site of
action for Z11-16:TFMK. We can exclude that the
inhibitory effect on behavioural response is due to
habituation because the moth behaviour in response to
puffs of Z11-16:TFMK was not statistically different
from that of control animals. Furthermore, EAG dose-
response curves confirmed the low intrinsic activity of
Z11-16:TFMK on the olfactory receptors, in spite of
the molecular structural similarity between the fluori-
nated analogue and the natural pheromone compo-
nent. Intensity and kinetic parameters of the EAG
responses of male antennae to Z11-16:Ac were altered
in the presence of Z11-16:TFMK, indicating that the
fluorinated analogue interacts with pheromone recep-
tion at the sensory organ level. A similar type of effect
was reported to occur with the well-known esterase
inhibitor 3-octylthio-trifluoropropan-2-one (OTFP)
in M brassicae 7
and in Antheraea polyphemus.6
In other
moth species, biochemical studies indicate that several
steps of olfactory reception are affected by TFMKs.
First, in vitro application to antennal extracts of Z11-
16:TFMK resulted in a moderate inhibition of the
antennal esterases of Spodoptera littoralis and Sesamia
nonagrioides with an IC50 (50% inhibition concentra-
tion) values of 121.0mM and 123.7mM, respectively (C
Quero, personal commun). This lack of specificity
toward antennal esterases, along with the close
similarity between the sex pheromones of S nona-
grioides and M brassicae led us to assume that Z11-
16:TFMK also inhibits the antennal esterase of the
latter insect, although this has not been tested yet.
Second, in the processionary moth, Thaumetopoea
pityocampa Schiff, aliphatic TFMKs bind to the
pheromone binding proteins (PBPs) in competition
with pheromone molecules.18
Similar results were
reported by Pophof et al,19
who proposed that, in A
polyphemus, the TFMKs can be bound to the PBP and
Table 3. Behavioural responses of Mamestra brassicae males to 3-s puffs of two blends of Z11-16:TFMK and Z11-16:Ac
Blend (mg) n
Responses
(%)
Latency (s)
(SD)
Cumulative activity
time (s) (SD)
Male activity
intensity (s) (SD)
Z11-16:Ac (0.01) 24 83.3 36.0 (54.9) 212.3 (130.6) 3379.7 (1651.6)
Z11-16:Ac (0.01) with Z11-16:TFMK (0.1) 22 68.2 NS 139.1 (224.7) P40.035 174.9 (154.4) NS 2576.8 (2089.3) NS
Z11-16:Ac (0.1) 9 100.0 6.3 (6.8) 277.8 (117.0) 4684.6 (2051.9)
Z11-16:Ac (0.1) with Z11-16:TFMK (1.0) 21 66.7 NS 75.5 (138.1) NS 242.5 (156.0) NS 3554.7 (2280.2) NS
Pest Manag Sci 58:839–844 (online: 2002) 843
Disruption of responses to pheromone by an analogue in M brassicae

6. transported to the pheromone receptor sites in
competition with the PBP–pheromone complex.
Mating disruption with a copy of the pheromone
blend has been successfully used as an environmen-
tally friendly method for pest control.20
Inhibitors of
behaviour have also been considered as an alternative,
or as additional compounds to improve communica-
tion disruption.1
In this regard, the addition to the
species-specific attractant blend of certain compo-
nents of the sex pheromone blends of congeneric or
sympatric moth species can cause cessation of oriented
flight in conspecific males. However, these inter-
specific inhibitors, although very efficient in reducing
male catches when mixed with the attractant, have not
proven useful as field disruptants. This is probably due
to the fact that these behaviour-antagonists are
detected by specialized receptor neurons on the insect
antennae as shown in M brassicae.14
This separate
detection of the attractant and its antagonist enables
male moths to discriminate strands of pure pheromone
amongst those containing antagonist. Recent investi-
gations have shown that male moths are able to
distinguish between odour sources separated in
space.21
Thus, a male moth still orients to a source
of pheromone when the inhibitor is released from a
source distant as little as 1mm.22
TFMKs have a
different mode of action, directly inhibiting the
responses of the olfactory receptor neurons tuned to
pheromone components. In dual-choice tests carried
out in a wind tunnel, we have noticed that S
nonagrioides males attracted to two dispensers baited
with pheromone and pheromone plus Z11-16:TFMK
showed no preference for either dispenser, but flight
tracks directed to the inhibitor-containing lure were
much more erratic than those directed to the inhibitor-
free dispenser.13
In conclusion, our data confirm that the TFMKs,
particularly those structurally analogous to the phero-
mone, inhibit the action of the pheromone at the
sensory and behavioural levels, which, together with
other data from the laboratory and the field, points to
the possible exploitation of such molecules in future
pest-control strategies.
ACKNOWLEDGEMENTS
The authors thank Jan Van der Pers (Syntech,
Hilversum) for designing the actograph and many
fruitful discussions, and two anonymous referees for
helpful comments on the manuscript. We are grateful
to Taylor Quadjovie for rearing the insects. We also
acknowledge CICYT for financial support
(AGL2000-1695-C02-01).
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M Renou, A Berthier, A Guerrero