364 MOSQUITOES OF NORTH AMERICA 



cage was divided across by a double partition consisting of 2 pieces of 16 mesh 

 gauze separated by a space 2 centimeters wide. Each compartment was pro- 

 vided with an opening for the hand. 



" The experiments were made exclusively with the stegomyia mosquito. They 

 were commenced on the 1st of June of this year. 



" On the 1st of June, 100 stegomyias, male and female, were let loose in the 

 large cage where they found dry food (sugar), but no water. In the cage was 

 placed the tub, three-quarters filled with rain water, and closed with 16 mesh 

 gauze. After six days all the mosquitoes in the cage had perished, evidently for 

 want of water. No mosquitoes had passed the 16 mesh gauze. No eggs were 

 found in the water, and no larvie developed there. 



" On July 4th, 200 stegomyia mosquitoes, male and female, were let loose in 

 the same cage. On the 9th there were only two insects left alive. On the 10th 

 these two were dead. No mosquitoes, eggs or larvae were found within the tub 

 or in the water. This experiment was, in every respect, a repetition of the first. 



" In the small cage the experiment was four times tried of placing three 

 unfecundated females on one side, and three males on the other. Both groups 

 were provided with food and water, and the females were occasionally allowed 

 to bite. These females had been obtained from pupae that had been kept iso- 

 lated, each one in separate bottles, so that all possible contact with the male 

 could be excluded. The double partition in the cage prevented the possibility 

 of contact through the partition. The males and females never passed through 

 the partition and the females were not fecundated. 



" The experiment was also repeatedly tried of keeping males and females 

 together on one side of the partition, and food and water on the other side. 

 Banana, sugar, molasses were tried separately. At times also the hand was kept 

 in the empty compartment for periods of from 30 to 40 minutes. If no water 

 was allowed on the side occupied by the mosquitoes they promptly died. Other- 

 wise they endured long, but were never able to pass across, nor could we ever 

 see any evidences that they made any attempt to push themselves across. 



" Another series of experiments were made by darkening one side of the cage 

 with a dark cloth. The mosquitoes were placed sometimes on the dark side, and 

 sometimes on the uncovered or light side. These insects were allowed food and 

 water during the experiment. They never passed through the partition. 



" It is my opinion that we may conclude from these experiments that the 

 stegomyia calopus can not pass through the wire gauze sent for trial. The gauze 

 is a 16 wire mesh ; that is, it presents 16 wires or threads to the linear inch." 



Dr. Samuel T. Darling, Chief of Laboratory of the Board of Health, Depart- 

 ment of Sanitation, Isthmian Canal Commission, in a paper entitled " Studies 

 in Eelation to Malaria," Washington, Government Printing Office, 1910, gives 

 the results of certain observations upon the size of mesh of wire screen. He finds 

 that at the Isthmus a 16-mesh screening answers the purpose against malarial 

 mosquitoes, but that against the yellow-fever mosquito, while practically safe, 

 it is not absolutely so. Out of several hundred mosquitoes, 8 species were able 

 to make their escape through a 16-mesh screen, as follows : 



Number of 



"Stegomyia calopus: ^Itclpil^ 



Males 10 



Females 6 



Culex cubensis, male 1 



Culex rejector, male 1 



Culex extricator, female 1 



Aedes angustivittatus, female 1 



Uranotcenia lowii, female 1 " 



