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The Use of Salt Solutions for the Demonstration of Physiological Differences between the Larvae of Certain European Anopheline Mosquitoes¹

Experiments with six forms of the Anopheles maculipennis complex and with Anopheles superpictus are discussed. Larvae were kept for three days at 27°C. in solutions of sodium chloride, potassium chloride, magnesium sulphate, and calcium sulphate, and the percentage of larvae surviving was recorded. By this means large numbers of experiments could be made, and the method may have a wide application in the study of larval survival and food requirements. It was found that the seven forms studied showed distinct differences in their toleration for the salt solutions used, differences which may be summarized thus:

Atroparvus. This species seems to have less need for calcium than any of the other species studied: a characteristic which enables some larvae to survive in relatively high concentrations of magnesium sulphate without the addition of a calcium salt. Atroparvus differs markedly in this regard from all other maculipennis forms studied. In the presence of calcium atroparvus is relatively tolerant of sodium chloride and it is somewhat more tolerant of potassium chloride than any of the other maculipennis forms. Comparison experiments with atroparvus material from North Germany, England, Portugal, Hungary, and Italy did not show any differences that seemed significant.

Labranchiae. The tolerance of this species for sodium chloride seems identical with that of atroparvus. It differs sharply from atroparvus, however, in its calcium requirements, and probably because of this it shows a greater mortality than atroparvus in solutions of magnesium sulphate and potassium chloride when calcium is not added. It is interesting that in experiments with minimum amounts of calcium sulphate labranchiae showed the same survival as subalpinus and typicus.

Subalpinus, typicus, and messeae. The experiments reported here do not show any very striking differences between these three forms. The messeae material available was inadequate for our purposes so that no experiments could be made with anything except sodium chloride and sea water, and the results of those experiments are contradictory. Subalpinus seems to be consistently more tolerant of sodium chloride than typicus, but the difference is not striking, and no differences are apparent in the experiments with other salts.

Sacharovi. This species differs markedly from all of the others in its greater tolerance of sodium chloride. The experiments with other salts were inadequate to form the basis of any conclusions.

Superpictus. The prime characteristic of this species is its inability to survive in media in which there is not a readily available supply of calcium. In the presence of calcium its tolerance for sodium chloride is similar to that of atroparvus.

¹ The studies and observations on which this paper is based were conducted with the support and under the auspices of the International Health Division of The Rockefeller Foundation.