Vol. xxix] ENTOMOLOGICAL NEWS 289 



are hardly noticeable. During some experiments recently car- 

 ried out in an attempt to incriminate this species with the 

 transmission of Dengue fever which proved negative and 

 were not completed 34 mosquitoes were allowed to become 

 gorged on one patient. These bites extended over a period of 

 five days. They did not cause the patient any itching or pain 

 except a few of them, less than 10 per cent., when the skin 

 was first pierced. Many times the patient could not feel the 

 mosquitoes biting at all. The writer afterwards received 97 

 bites from these same mosquitoes during a period of 10 days. 

 The only sensation experienced was an occasional slight sting 

 when the mouth parts were first inserted. A slight itching 

 sensation developed in a few of the bitten areas several days 

 later when accidentally rubbed or irritated. 



Although M. titillans is present throughout all months of 

 the year in the Canal Zone, it is most abundant from late April 

 to early October. During this period it is more numerous in 

 the lake region, and is also found at greater distances from 

 the lake. 



While investigating the abundance of this species on the 

 west side of the lake, we visited Mr. J. A. Forsyth on board 

 the house-boat Hyacinth on the evening of October i, 1915. 

 Mr. Forsyth is in charge of the destruction of the water hya- 

 cinths in Gatun Lake. While searching for the hyacinths he 

 visits many obscure parts of the lake, and has been kind 

 enough to keep me informed of the status of the Pistia, and 

 has assisted in my observations on this plant in many ways. 

 He had previously informed me of the hosts of mosquitoes 

 that paid nightly visits to the house-boat. Owing to this in- 

 formation an evening visit was made for the purpose of inves- 

 tigation. The boat was anchored about 200 yards from the 

 shore in an arm of the Cano River region, at the west side 

 of the lake, about one and one-half miles west of the Canal 

 route. Two miles west of the place of anchorage the surface 

 of the water, several square miles in area, was covered with 

 packed masses of the Pistia plants. All the living quarters of 

 the boat were well screened. The fore deck was 



