Jan. 1923] annual report 23 



Spraying for Apple Maggot. 



For the third season a study to shed further light on the effects of spray- 

 ing with arsenate of lead and water was made by W. C. O'Kane. 



The plan of the experiments includes thorough spraying of all apple trees 

 in an area that is protected by natural boundaries from ingress of flies mi- 

 grating from unsprayed trees. No attempt is made to attract the flies by 

 means of bait. The purpose is to distribute drops of poison spray over the 

 foliage in such abundance that any female flies sipping moisture from the 

 foliage will be poisoned before they have had opportunity to lay eggs. 



Trustworthy information is difficult to secure in the case of this insect. 

 Its abundance fluctuates in marked degree from year to year. It may be 

 numerous in a given locality for a series of seasons and suddenly become 

 relatively scarce. Friiit may be badly attacked in a certain area and relative- 

 ly free from attack in another area near by. For these reasons it is necessary 

 to exercise special caution in drawing conclusions from records of infestation 

 following spraying. If the species turns out to be scarce in orchards where 

 spraying is carried out, the lack of abundance may be a result of the spraying 

 or may be due to some other cause. The factors that enter into the matter 

 are so complex and often so obscure that positive conclusions are excep- 

 tionally difficult or may be entirely out of the question. 



In view of these circumstances, the present investigation is being con- 

 tinued for several seasons; and any interpretations or conclusions will be 

 withhekl until the work is completed. 



In the crop season of 1922 experimental spraying was carried out in three 

 different areas. In each of these areas the infestation by apple maggot was 

 light; whether this was due to the spraying or to other causes cannot be 

 safely asserted. 



Control of Black Flies. 



In the fall and winter of 1921 facts of unusual interest were secured in 

 the life history of black flies. A considerable number of streams have been 

 observed by Mr. O'Kane in the course of this study. Notes have been taken 

 at rather frequent intervals, showing the abundance of larvae in the streams, 

 the relative amount of stream flow, the temperature of the water and other 

 data. Specimen larvae have been collected in each case and the species 

 determined. 



In the late fall of 1921 a long-continued drouth caused various streams 

 to dry up where black flies normally breed in numbers. These breeding 

 grounds were kept under careful observation and were visited after the first 

 snows had fallen. They were again visited early in 1922, and at intervals 

 as the spring and summer progressed. The result is a series of records which 

 shed new light on the seasonal abundance and the breeding habits of black 

 flies. 



The breeding points in question will be kept under observation until the 

 winter season of the current year. It is expected that the results of the 

 general study will then be pubhshed. 



