Studies on the age of mosquitoes : I. The determination of physiological age of Culex pipiens pallens by the relics formed at ovarioles after the oviposition

Abstract

In the present paper the formations of relics at the pedicles of ovarioles after oviposition were clearly shown with the colonies of mosquitoes of Culex pipiens pallens, Culex tritaeniorhynchus, Aedes togoi and Armigeres subalbatus, which were reared in the laboratory. The adult females of mosquitoes were individually reared in the test tubes so that one may control the times of blood-feeding and oviposition. The observations of the changes in ovaries were made at each gonotrophic cycle. The sac-like dilatations at the pedicles of Culex pipiens pallens were found to complete their contraction in twenty-four hours after expelling the eggs. The maximum number of relics per pedicle was observed exactly correspond to the number of ovipositions of each mosquito. Therefore it was shown that the maximum count of relics per ovariole can be utilized for expressing the physiological age of mosquitoes of above mentioned species of this country. The rate of number of ovarioles which have the maximum number of relics was, however, found to be rather lower than expected. It was around one third of all observable ovarioles at the first gonotrophic cycle, around one tenth at the second and around one twentieth at the third cycle. It was emphasized that the observation should be carefully made not to miss the small number of those ovarioles in order to determine the age of mosquitoes correctly.