Torres et al.: Energetics of larval Saaenops ocellatus 



759 



Nitrogen excretion rate 



Absolute ammonia excretion rates (Y, j.ig/ind./h) in- 

 creased with increasing mass (X, mg) in larvae fed to 

 satiation according to the relationship Y= 0.277X 0128 

 (r^O.58) (Fig. 3). The slope of the excretion vs. mass 

 curve in fed larvae (0.728) indicates that mass-specific 

 ammonia excretion declines with increasing mass. 



The relation between ammonia excretion and mass 

 was substantially changed with a 24-h period of star- 

 vation, such that Y = 0.058X 328 (r 2 =0.40) (Fig. 4). 

 The change indicates that absolute ammonia excre- 

 tion in starved individuals is roughly 50% that of fed 

 individuals. In addition, the decline in mass-specific 

 ammonia excretion with increasing mass is more pro- 

 nounced as is indicated by the lower slope (0.328). 



The increasing mass of growing larvae fed to sa- 

 tiation resulted in an increase in absolute ammonia 



excretion with age (Fig. 3). Starvation resulted in 

 about a 50% decline in the slope of the relationship 

 between excretion and age, similar to that observed 

 in excretion vs. mass. 



The percent contribution of ammonia and urea to 

 total excretion differed; urea dominated in starved 

 individuals. Urea in starved larvae (as total N ex- 

 creted) was twice that of fed larvae (Table 3). 



O.N ratios 



The low 0:N ratios based on both ammonia-N 

 (0:NH 3 ) and total nitrogen (ammonia-N and urea- 

 N) excretion rates indicated that protein was the 

 combusted fuel (Table 4). 0:NH 3 ratios ranged be- 

 tween 4 and 12 for all ages. 0:N values based on com- 

 bined ammonia-N and urea-N excretion were lower, 

 ranging between 1 and 9. Larvae starved for 24 h 



