First published online February 4, 2005
Journal of Experimental Biology 208, 787-796 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01431
Associative learning of plant odorants activating the same or different receptor neurones in the moth Heliothis virescens
H. T. Skiri1,
M. Stranden1,
J. C. Sandoz2,
R. Menzel3,4 and
H. Mustaparta1,4,*
1 Neuroscience Unit, Department of Biology, Norwegian University of Science
and Technology, Olav Kyrres gate 3, NO-7489 Trondheim, Norway,
2 Research Centre on Animal Cognition, Paul Sabatier University, 118 Route
de Narbonne, FR-31062 Toulouse cedex 4, France,
3 Institut für Biologie-Neurobiologie, Freie Universität Berlin,
Königin Luise Straße 28-30, DE-14195 Berlin, Germany
4 Centre for the Biology of Memory, Norwegian University of Science and
Technology, Olav Kyrres gate 3, NO-7489 Trondheim, Norway
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Fig. 1. Acquisition curves obtained in classical conditioning experiment with four
concentrations of racemic linalool associated with a sucrose reward
in H. virescens females (A) and males (B). The proportion (%) of
insects showing the PER in each of the 12 conditioning trials is shown. The
ISI was 2.5 s. (C,D) The proportion of insects with PER at different points of
time (15 and 120 min) after the conditioning trials. The number of individuals
included in each group is given above the bars for the 15 min test. An
increased percentage of both females and males showed the PER when trained to
increasing racemic linalool concentrations.
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Fig. 2. The proportion of H. virescens females (A) and males (B) that
showed the PER 1 h after conditioning experiments using 100 mg
racemic linalool associated with a sucrose reward at five different
ISIs (-1, 0, 1, 2 and 3 s). The interval of 1 s gave the best performance with
44% of the females and 36% of the males responding to the odorant. The groups
differing significantly from each other (Fisher's exact test with Bonferroni
correction; P<0.005) are marked with `a' vs `b'. The
number of insects in each group is given within the bars.
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Fig. 3. (A) Learning rate of H. virescens females showing the conditioned
response (proboscis extension) to different concentrations of the odorants
racemic linalool, ß-ocimene and ß-myrcene in extinction
tests. The tests were performed 15 min after a 10-conditioning trial
procedure. A lower threshold for learning and for the maximum proportion of
insects responding were obtained for racemic linalool as compared to
the two other odorants. Insect numbers were 36-39 for all groups except for
the additional group conditioned to racemic linalool at 0.001 mg
(N=49). (B) Dose-response relations as electroantennograms (EAG) for
the different concentrations of the three odorants racemic linalool,
ß-ocimene and ß-myrcene obtained in H. virescens females.
The responses are given as percentages of the response to 10 mg
racemic linalool and as the average of the responses to the two
parallel test series in five female moth antennae. The lowest concentration
was tested in two individuals only. The mean response to the control (air) was
subtracted from the odorant responses, which explains the slightly negative
response values for some of the lower odorant concentrations. The dotted line
shows the mean response to the other control (hexane evaporated on filter
paper). Error bars indicate the standard error of means. (C) The learning rate
(% proboscis extension in A) plotted as a function of the EAG response (% of
the 10mg racemic linalool standard in B) showed a significant
correlation (Pearson R correlation coefficient).
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Fig. 4. (A) Learning rate of H. virescens females showing the conditioned
response (proboscis extension) to CS+ and CS- (irrespective of which odorant
was the CS+) in extinction tests after differential conditioning with the
three odorant pairs [racemic linalool (L) and ß-myrcene (M), L
and ß-ocimene (O) and O and M, 12 conditioning trials, N=103-106
for each pair)]. The concentrations used were 0.1 mg racemic
linalool, 10 mg ß-ocimene and 100 mg ß-myrcene. The moths responded
significantly more to the CS+ in all cases (exact McNemar test,
P<0.05). (B) Learning rate in extinction tests after differential
conditioning with the six pairs of three odorants [each odorant (CS+ and CS-)
was presented pseudo-randomised six times, N=51-53 for each pair].
There was a significant discrimination between the CS+ and CS- in the M+L-,
M+O- and O+M- groups (exact McNemar test, P>0.05, marked with an
asterisk). For the odour pair M L, an asymmetry appeared as the insects showed
a significantly higher discrimination when M was the rewarded odorant than
when L was the rewarded odorant CS+ (Fisher's exact test,
P<0.05).
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© The Company of Biologists Ltd 2005
