Because saccharin is also sweet tasting to people, I expected the flies to respond positively to it as well. We stuck flies to popsickle sticks by pushing their wings into a sticky wax we rubbed on the sticks. We tested the flies' sensory perception by giving each fly the chance to feed from each sugar, starting with the lowest concentration and working up and rinsing the flies between tests. Hardly any flies responded to saccharin. The results supported my first hypothesis that sucrose would be the most detectable sugar by the flies.
Flies show a selectivity of response to sugars based on molecular size and structure.
Glucose, the smallest of the three sugars, is a monosaccharide. The threshold value of glucose was the highest in this experiment because a higher concentration of this small sugar was needed to elicit a response. Maltose and sucrose are both disaccharide. Because sucrose is an alpha- glucosidase derivative, it makes sense that the threshold value for sucrose occurs at a lower concentration than that for maltose. I think this might also be the reason why sucrose tastes so sweet to people.