Figure 3.

Feeding. Groups of 30 larvae are allowed to feed on petri dishes filled with dyed agarose which contains either fructose (FRU) or sucrose (SUC) at the indicated concentration; the amount fed then is quantified photospectrometrically. Values from a group which is allowed to feed on dyed agarose without any sugar added serves as baseline; absorbance values of this group are subtracted from the spectrometer readings of the experimental groups to yield the feeding score. Therefore, feeding scores greater than zero indicate that the larvae eat more than if sugar were absent, and feeding scores below zero indicate that larvae eat less than in the absence of sugar. (A) Fructose enhances feeding at low but suppresses feeding at higher concentration. (B) Sucrose also leads to increases in feeding at low but to decreased feeding at higher concentration. We use Kruskal–Wallis tests for all-group comparisons at P < 0.05; for single-group comparisons against zero, 1-sample sign tests are used at P < 0.05/4. For details concerning the box plots, see the caption of Figure 1.