Forces Necessary to Release the Staminal Lever in 13 Salvia Species

Average Force Necessary to Trigger the Lever (mN) ± Number of Number of

Salvia Species Standard Deviation Measurements Flowers

Average Force Necessary to Trigger the Lever (mN) ± Number of Number of

Salvia Species Standard Deviation Measurements Flowers

S. amplexicaulis

1.2 ± 0.9

17

10

S. forskahlii

2.9 ± 0.9

65

10

S. glutinosa

1.6 ± 0.8

10

3

S. cf. microphylla

10.0 ± 5.3

22

3

S. nilotica

0.5 ± 0.2

25

2

S. nubicola

1.0 ± 0.7

26

4

S. phlomoides

1.1 ± 0.2

25

2

S. pratensis

2.7 ± 0.3

28

5

S. sclarea

5.2 ± 3.0

43

7

S. transsylvanica

3.0 ± 0.7

20

3

S. uliginosa

0.9 ± 0.3

6

1

S. verbenaca

2.7 ± 1.1

49

5

S. viridis

1.5 ± 0.5

15

3

Note: Measurements were performed with a metal sensor of 0.6-mm diameter, mimicking a bee's proboscis. In plants where the lever is not triggered by the bees proboscis but by the bee's head (S. forskahlii, S. glutinosa, S. nilotica, and S. nubicola), a wider sensor (1 to 3 mm) was used to trigger the lever.

Note: Measurements were performed with a metal sensor of 0.6-mm diameter, mimicking a bee's proboscis. In plants where the lever is not triggered by the bees proboscis but by the bee's head (S. forskahlii, S. glutinosa, S. nilotica, and S. nubicola), a wider sensor (1 to 3 mm) was used to trigger the lever.

A maximum force of 407 mN was recorded with a simulated proboscis length of 6 mm and a maximum force of 167 mN for a simulated proboscis length of 8 mm in big S. sclarea flowers with 9.7 mm flower-tube length. The maximum force recorded for small flowers (flower-tube length 9.4 mm) was 260 mN and 45 mN for a proboscis length of 6 mm and 8 mm, respectively (Figure 6.8). Using even shorter proboscis lengths was not possible because the flowers were destroyed by the head mounted on the sensor if the proboscis length was shorter than 6 mm. The shorter the length of the simulated proboscis, the earlier the insect's head has to be squeezed into the tight corolla tube, resulting in an earlier onset of force increase and in a higher maximum value of force needed to reach the nectar at the base of the corolla tube (Figure 6.8).

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