Brachymeria lasus: effects of nutrient level on in vitro larval growth of a chalcid insect parasite.

Exponential weight gain equations and growth rates were determined during larval development of Brachymeria lasus reared aseptically on chemically defined media with varying amino acid and glucose levels. The rate of weight gain increased from 0 to 2% dietary glucose and mean growth rate increased from 160 to 260 micrograms/mg x day. Similar results were observed for larvae reared on media containing 1 to 4% free amino acids. At higher nutrient levels, growth rate and rate of weight gain declined and maximal growth occurred at dietary osmolalities of 500-700 mOsm/kg. A further experiment utilizing nutritionally inert L-glucose suggested that this osmolality range does not reflect the optimal for growth but rather the point at which the detrimental effects of dietary osmotic pressure exceed the nutritive benefit of the dietary ingredients.