81 



RESISTANCE OF THE EGGS OF STEGOMYIA FASCIATA (AEDES 

 CALOPUS) TO CONDITIONS ADVERSE TO DEVELOPMENT. 



By Malcolm Evan MacGregor, B.A. (Cantab.), 

 Wellcome Bureau of Scientific Research. 



It is a well-known fact that the eggs of Stegomyiafasciata are highly resistant to 

 conditions adverse to their normal development. 



In April 1915 I received through the Colonial Office a few dried leaves from West 

 Africa, on which— secured by a fine mud deposit— were eggs of this mosquito that 

 had been in a dried condition for at least three and a half months. These were found 

 to be viable and were successfully hatched and reared for many successive generations, 

 as described in a recent paper.* 



The eggs as they reached me showed on examination that some were normal- 

 looking, while many were partially, and others completely, collapsed. The partially 

 collapsed eggs no longer had the evenly rounded surface of the normal egg, but the 

 surface presented depressions such as would result from shrinkage of the contents 

 and the falling in of the shell. This had reached such a degree in the completely 

 collapsed eggs that the shell on one side was in contact with that on the other, and 

 either the egg had attained the shape of the bowl of a spoon, or had taken on the 

 triangular form shown in section in fig. 1 («). 



Fig. 1. Diagram of section through coUapsed eggs 



of Stegomyiafasciata; a, triangular form ; 



b, spoon-shaped form. 



When the leaves, however, were placed in water, the number of larvae that hatched 

 out tended to convince me that at least many of the partially collapsed eggs had been 

 viable as well as those that looked normal. This fact has led me to study the eggs 

 that have been laid by the subsequent generations of these mosquitos \vith a view to 

 finding out the powers of resistance they possess. 



Soon after having established means of keeping the strain going actively, it was 

 found that, by the methods adopted, the eggs that were laid in large numbers, 

 and which would always hatch out vigorous larvae, were highly susceptible to 

 destruction by desiccation. 



♦"Notes on the Rearing of Stegoviyia fasciata in London." Journal of Tropical 

 Medicine and Hygiene, 1st Sept. 191.5. 



(C250) F 



