The Hydrogen Ion Concentration of the Digestive Fluids and Blood of the Codling Moth Larva*

Abstract

The pH of the digestive fluids of 1st instar and nearly mature codling moth (Carpocapsa pomonella) larvae was detd. colorimetrically and the determinations for the latter verified potentiometrically. The crop and ventriculus of the 1st instar larva appear to have a pH value of approx. 8.5. This value may become somewhat higher as the larva approaches maturity. The digestive fluids are evidently well buffered, hence ingestion of large amts. of apple pulp or juice (pH 3.3; titratable acid 0.6% as malic acid) did not appreciably alter their active alkalinity. The importance of the pH of the digestive fluids in relation to control by stomach poisons is discussed. The pH of the blood of nearly mature codling moth larvae is 6.7-6.8.