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utilization and efficiency. Relationships between many of these terms 
are discussed by Kozlovsky (1968) and Waldbauer (1968). 
As an index of digestibility the ratio of the amount of food 
assimilated to the amount of food ingested, referred to as the 
‘Assimilation Efficiency’ (Odum, 1971) or the ‘Coefficient of Di- 
gestibility’ (Waldbauer 1964, 1968, House 1965), was used. In 
practice, this measure is only an approximation since the numerator 
(as determined by the standard gravimetric technique) does not 
quite represent the amount of food actually assimilated (Waldbauer 
1968). This slight error is due to the presence of metabolic wastes 
in the feces in addition to the undigested food (Lafon 1951), but 
Hiratsuka (1920) and Waldbauer (1964, 1968) point out that this 
difference between true and measured assimilation efficiencies is 
negligible. 
The efficiency with which ingested food is converted to biomass 
is calculated by dividing the dry weight of food ingested into the 
dry weight gained by the larva. This index, referred to by physiolo- 
gists as the ‘Efficiency of Conversion of Ingested Matter’ (Wald- 
bauer 1968) and by ecologists as the ‘Ecological Growth Efficiency’ 
(Odum 1971), is an overall measure of an animal’s ability to utilize 
for growth the food ingested. 
The efficiency with which digested food is converted to biomass is 
calculated by dividing the dry weight of food assimilated into the 
dry weight gained by the larva. This index, referred to by Wald- 
bauer (1968) as the ‘Efficiency of Conversion of Digested Matter’ 
and by Odum (1971) as the ‘Tissue Growth Efficiency’, decreases 
as the proportion of digested food metabolized for energy and main- 
tenance of physiological functions increases (Waldbauer 1968). 
The relative growth rate is calculated by dividing the mean dry 
weight of the larva times the duration of the instar in days into the 
dry weight gained by the larva during the stadium (Waldbauer 
1968). This index reflects the rate at which biomass is added by a 
larva corrected for any size differential between groups of larvae. 
The ‘Respiratory Coefficient’ (Lindeman 1942) is described as 
the ratio of respiratory and maintenance loss to the net secondary 
production or biomass increase. This coefficient is calculated by 
dividing the total calories lost through respiration and maintenance 
by the total calories added to the insects’ biomass. This ratio is 
what may be termed an ‘Energy Production Cost Ratio’ ; the smaller 
the coefficient or ratio, the more efficient the larva is at allocating 
energy to biomass, the larger the coefficient, the greater the number 
