Regulation of hemolymph and whole-body Mg ++ concentration was studied in the larvae of Aedes campestris Dyar and Knab from a salt-lake containing 190 m Eq Mg++/litre. Hemolymph Mg++ concentration of the larvae responded quickly to a change in external Mg++ concentration and reached a new level after one day. Over a wide range (0.02 to 200 m Eq/litre) of external Mg++ concentrations the blood Mg++ concentration changed only from 4 to 8 m Eq/litre. The rate of entry of Mg++ into the larvae by drinking was 19 to 57 n Eq/mg x hr. Drinking rate was found to be independent of temperature (10C- 22C), Mg++ concentration (100- 300 m Eq/litre), and presence of particles in the medium. More than 95% of the ingested Mg++ was absorbed from the midgut. Whole-body Mg++ content of larvae remained low, indicating that excess Mg++ was not stored in tissue. Measurement of urine Mg++ concentrations of animals in different media showed that excretion via urine could account for all of the ingested Mg++. Anal papillae need not therefore be implicated in Mg++ excretion in Aedes campestris larvae. / Science, Faculty of / Zoology, Department of / Graduate

The basic morphology and ultrastructure of the anal papillae of a saline water mosquito larva (Aedes campestris) have been investigated under two physiological conditions: (a) normal hyperosmotic external medium and (b) dilute hyposmotic medium. The ultrastructure of these organs suggests that they are not rudimentary, but rather are made up of cells that are morphologically specialized for transport. The anal papillae appear active in both the normal and dilute media and possible functions under the two physiological conditions are discussed. No major qualitative or quantitative differences were observed with the large change in external medium. This suggests that physiologically-demonstrated adaptive changes may require only minor structural alterations. The morphology and ultrastructure of the hind gut of A. campestris larvae were compared under two physiological conditions; normal (requiring hyporegulation) and dilute (requiring hyperegulation) external medium. No differences which might be associated with hyporegulation were observed. The rectum of A. campestri s was compared to that of Aedes aegypti. The rectum in the former is composed of two regions, an anterior and posterior rectum, while in Aedes aegypti, an exclusively freshwater mosquito larva, the rectum has only a single region. The rectal epithelia in both insects studied have morphological specializations for water and ion transport, and a consideration of quantative differences suggests that the posterior rectum is unique to Aedes campestris and hence could be responsible for the ability of this species to produce hyperosmotic urine. When the posterior rectal epithelium is compared to similar transporting epithelia in previously-studied terrestrial insects, several ultra-structural differences were noted. It is suggested that the mechanism of hyperosmotic urine production in saline water insects may be different from that in terrestrial insects. Several possible mechanisms of hyperosmotic urine production are discussed. / Science, Faculty of / Zoology, Department of / Graduate