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(e) Behavioral Assays
A 200 x 80 x 80 cm wind tunnel was used for behavioral tests. A Fischbach speed-
controller fan (D340/E1, FDR32, Neunkirchen, Germany) pushed air through
the tunnel with an air velocity of 0.35 m s -1 . Four charcoal filters (145·457 mm,
carbon thickness 16 mm, Camfil Farr, Reinfeld, Germany) cleaned the incoming
air. The experiments were performed at night with red light illumination (< 0.01
µ E) 1-3 h after the start of the dark period. An hour prior to testing, the moths
were exposed to ambient room temperature (20°C), RH (65%) and experimental
light conditions. Naïve moths were tested individually in the wind tunnel. Each
moth was placed in an open glass tube mounted on a stand at the downwind side
of the tunnel. At the upwind end were set two freshly collected flowers of S. latifo-
lia (from the Swiss population) of different sexes and approximately equal corolla
size (to avoid an effect of flower size). A distance of 20 cm separated the two flow-
ers in order to ensure that the moth's response entirely depended on scent source.
After take-off, each moth was followed visually until it landed on one of the two
flowers, which always resulted in proboscis extension and nectar drinking.
(f) Statistical Analysis
All data were tested for homogeneity of variances (Levene's test) and for
normality (Kolmogorov-Smirnov test). We used a GLM approach to exam-
ine the effects of sex and population on mean absolute odor emission. Log-
transformed total amount of odor was used as dependent variable and sex
and population as factors. Floral diameter was used as covariate to correct
for flower size. Nonparametric Mann-Whitney U-tests were used to analyze
the differences in absolute amounts of individual compounds and of flower
numbers between males and females in each population separately, since no
transformation allowed analysis with a parametric test. Flower diameter was
analyzed by a t-test. Frequency of moth choices were compared using a Chi 2
test. All analyses were carried out using SPSS 11.0.4 for Mac OS X (SPSS
Inc., Chicago, USA).
Authors' Contributions
MOW collected and analyzed data, and wrote part of the manuscript, PAP per-
formed bioassays with moths, AW designed the experiments, FPS designed exper-
iments, analyzed data, and wrote part of the manuscript. All authors contributed
to the discussion, read and approved the final manuscript.
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