66 THE REPORT OF THE No. 38 



Results. Excellent results were secured from this treatment. With the 

 exception of some larvse present on the plants for a short time after treatment, 

 no midge has been seen up to the present. 



Other Corroborative! Results. The tobacco dust remedy proved equally 

 effective in two other greenhouses — one in Toronto and the other in Grimsby. 



It is of interest to note that at Ivey's Conservatories, Port Dover, good results 

 in the control of midge were secured by covering all the rose beds early in the 

 season with a heavy coat of finely cut tobacco stems. The beds were watered as 

 usual, and it would appear that the nicotine washed in this way from the stems 

 destroyed practically all the insects in the soil, because throughout the season no 

 infested plants were found except in one section. This particular section was 

 treated with tobacco dust in September, and Messrs. Ivey are now pretty con- 

 fident that they have wholly eradicated the pest. 



SOME MOSQUITO PROBLEMS OF BRITISH COLUMBIA. 



Eric Hearle, Entomological Branch, Ottawa. 



British Columbia has many serious mosquito problems with which to cope. 

 She is not alone in this respect, for, on the Atlantic coast, in Northern Ontario 

 and Quebec, and in certain of the Prairie province's, mosquitoes occur in such 

 numbers as to be of economic importance. The mountain province has, however, 

 conditions and problems peculiar to herself, which are very different Jrom those 

 found elsewhere in Canada, 



In British Columlbia the huge ranges of mountains and the rivers fed by 

 their melting snows constitute the main factors determining mosquito abundance. 

 Other important factors are the climatic conditions, which determine whether 

 the snow shall melt gradually or shall melt so suddenly that the rivers are unable 

 to carry off the water sufficiently fast to prevent the flooding of the low-lying lands. 

 The main mosquito problems of British Columbia are caused by those species of 

 the mosquito fauna which breed in the flooded bottom lands bordering the rivers. 



The Lower Fraser Valley Problem. 



For the last two years a detailed study has been conducted of the serious 

 mosquito problem presented in the Lower Fraser Valley. By means of automo- 

 bile, motor boat and canoe, larval and adult surveys were made over an area of 

 more than two thousand square miles. These, life history and laboratory experi- 

 ments, and aerial surveys over some of the main breeding areas have resulted m 

 the accumulation of sufficient data to indicate the important factors in the prob- 

 lem. 



The Fraser river emerges below Hope from the precipitous, rocky, Fraser 

 canyon into the Fraser delta — a broad low-lying valley of over two thousand square 

 miles. The low elevation may be gauged from the fact that at the town of Mission, 

 about forty miles from the coast, the altitude is only twenty-one feet above sea 

 level. The dyking of huge tracts of land has appreciably reduced the mosquito 

 breeding places; but there remain along the river many extensive low-lying areas 

 capable of flooding at high freshets, and which are the cause of the mosquito 

 trouble in the district. The height of freshet varies considerably. In 1919, the 

 river rose 17' 4" (at Mission) and there was no mosquito pest. In 1920, the 

 river rose 21' 0" (at Mission) and a very serious pest resulted. 



