Experiments upon respiration in the larvæ of certain parasitic hymenoptera

Abstract

The object of the work described was to obtain some direct evidence as to the alleged respiratory function of the "tail" of endoparasitic Ichneumonid larvae and the "''''"caudal vesicle" of Braconids. Methods of biological indicators for studying the oxygen absorption are described in detail. The flagellate Polytoma uvella was the form found to be the most useful, since oxygen tension was shown to be the main factor controlling its movements. The luminous B. phosphorescens was also employed, the luminescence of which is dependent on the presence of oxygen. CO2 output was investigated mainly by means of pH indicators. The "tail," which is such a characteristic feature of many 1st instar Ichneumonids, is of no importance for respiration. As for the caudal vesicle of the Braconids, there are considerable differences of structure in different genera. Where the vesicle is large and supplied with a good blood circulation, expts. show it to be of undoubted importance as a respiratory organ. It is, however, not the sole, nor even the most important, organ of respiration, gas exchange taking place over the whole body surface. In Apanteles and Micro-gaster the vesicle, when at its maximum development, cannot be responsible for more than about ^ of the total respiration. In other forms, e.g., Orgilus, its respiratory function is less.[long dash]Other theories as to the function of the caudal vesicle are briefly discussed.