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First published online December 14, 2006
Journal of Experimental Biology 210, 37-45 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02616
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Flower tracking in hawkmoths: behavior and energetics

Jordanna D. H. Sprayberry1,* and Thomas L. Daniel2

1 Arizona Research Laboratories, Division of Neurobiology, University of Arizona, Gould-Simpson Building Room 611, 1040 E. 4th Street, Tucson, AZ 85721, USA
2 Arizona Research Laboratories, Division of Neurobiology, University of Washington, 98195, USA


Figure 1
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  		Fig. 1. (A) Line drawing showing the dorsal (mirror) view of a moth feeding from the robotic flower. All axes of motion are defined relative to the moth's perspective. The two axes illustrated are the horizontal axis (H), the moth's left and right, and the looming axis (L), approach-recede. The vertical axis (V, dotted line), is coming out of the page and is up-down for the moth. (B) A schematic showing how we determined the feeding time used for calculating feeding rates. The thick black line shows distance between the moth's head and the base of the flower (MFD). The broken line across the graph represents the maximum distance from the flower at which the moth's proboscis could contact nectar (calculated based on average proboscis length of the colony). Feed time was defined as (the last time MFD < broken line) - (the first time MFD < broken line). The feeding rates were calculated as (amount of nectar consumed)/(feed time).

 

Figure 2
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  		Fig. 2. The mean feeding rate across frequency and direction; the lines for different direction treatments are labeled (H, horizontal; V, vertical; L, looming). Feeding rates measured from moths tracking flowers moving in the L axis (approach-recede) are significantly lower than those for control flowers (ANOVA, Tukey's HSD P<0.05), but there were no frequency effects when using a multifactor ANOVA.

 

Figure 3
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  		Fig. 3. The variance of flower to moth distance measurements during feeding bouts. The lines for different direction treatments are labeled (H, V and L). The variance for the L direction 2 Hz treatment was significantly higher (P<0.05, ANOVA, Tukey's HSD).

 

Figure 4
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  		Fig. 4. (A) Sample input data of a moth (gray line) following a flower (black line) in the V axis (up-down) at 2 Hz. (B) The resulting cross correlogram: the values for rm and latency (l) are taken from the circled peak, the first peak after zero.

 

Figure 5
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  		Fig. 5. The mean cross correlation coefficient, rm, for all treatments. Frequency is on the x axis, and the lines for different direction treatments are labeled (H, V, L). Mean rm values for tracking ability start to fall off at 2 Hz for moths feeding from flowers moving in the L axis. Moths were unable to track 3 Hz L axis flowers. Both H and V axes flowers have high correlation coefficients for 1 and 2 Hz.

 

Figure 6
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  		Fig. 6. The delay characteristics of M. sexta's flower tracking ability. (A) Latency of response plotted against frequency. (B) Phase of response plotted against frequency, where phase is defined as (latency of response)/(period of flower motion). A value of zero indicates that the moth is perfectly in phase with the flower, while a value of 0.5 indicates the moth is 180° out of phase. The direction treatments are labeled (H, V, L).

 

Figure 7
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  		Fig. 7. The results of an FFT analysis on one feeding bout (direction=V axis; frequency=3 Hz). This is how the frequency and amplitude coefficients for calculating rate of energy gain were obtained. Discarding the first peak, which is an artifact due to removing the mean position (see Materials and methods), the remaining three highest peaks are the coefficients used (all included peaks are circled). (A) shows the FFT of moth position for the H axis, (B) for the V axis, and (C) for the L axis.

 

Figure 8
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  		Fig. 8. The results of an energetics model that used flight path and feeding data to calculate energy gain for all treatments. Direction treatments are plotted as separate, labeled lines (H, V, L), while frequency is shown on the x-axis of the plots. Values are means ± s.e.m. (A) Rate of energy in, calculated using measured feeding rates. (B) Rate of energy out, calculated using coefficients from an FFT analysis of the moths' paths during feeding bouts. While the increase in energy out is statistically significant (ANOVA, P<0.05), it is minute compared with the energy in. (C) Rate of energy gain. Energy gain patterns mimic patterns of feeding rate.

 




© The Company of Biologists Ltd 2007