S S S G S

Figure 2.8 Crop-emptying rates and metabolic rates in honeybees collecting sugar solutions of different concentrations. (a) Sugar content of the crop as a function of time in bees which collected 30 ml of each sucrose (S) or glucose (G) concentration (means ± SD). (b) Comparison of crop-emptying and metabolic rates, both expressed as mg sugar h_1 (means ± SD). Only the rates for 7.5% sucrose were significantly different from the others.

Source: Reprinted from Journal of Insect Physiology 45, Roces and Blatt, 221-229. © 1999, with permission from Elsevier.

possible upregulation of gut function in response to declining nutrients (Woods and Chamberlin 1999). Decreased secretion of digestive enzymes after exposure to low substrate concentrations, or decreased absorption of the products of hydrolysis, does not seem an efficient way to maximize the value of low-nutrient diets (Simpson et al. 1995). Passive absorption of nutrients provides a mechanism for matching the rate of absorption to the rate of hydrolysis (Pappenheimer 1993), so absorption

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