May, 1921] BIENNIAL REPORT. 11 



was made in determining the repellent qualities of this mixture with reference 

 to the adults of the cabbage root maggot. 



Preliminary to the growing season of 1919 a survey of root maggot infesta- 

 tion was made in order to discover a favorable location for the summer's work. 

 During the prior two seasons the species had proved insufficient in number to 

 afford suitable material in the places where experiments were in progress. In 

 the study of this insect, an abundance of material is the first requisite. Follow- 

 ing the survey it was determined to transfer the season's work to the southern 

 edge of the town of Pelham, where records showed heavy infestation in 1918. 

 As the crop season of 1919 developed it became evident that the infestation in 

 Pelham would not be as heavy as indicated. Nevertheless, definite and valu- 

 able progress was made along certain lines of the investigation. 



As in prior years, cabbage and radish were used in the experiments. 



Two grades of tobacco dust were employed : one grade a finely powdered dust 

 ground to a condition resembling flour, the other a coarsely ground material 

 containing many granules and pieces of stem an eighth of an inch to a quarter of 

 an inch in length. A comparative study was made of the relative repellent 

 qualities of the two materials. 



Analysis of the results showed no considerable difference in repellent quali- 

 ties, and indicated that the degree of fineness is not a factor of importance in 

 determining the efficiency of the tobacco ingredient, so far as its effects on the 

 adults are concerned. 



Further experiments were carried out to disclose the effect of dilution with 

 agricultural lime in varying proportions. The results showed that the repel- 

 lent qualities of the mixture are not materially decreased by dilution up to two 

 parts of lime to one part of tobacco dust, and the dilution may be carried to 

 four parts of the lime to one part of tobacco dust without serious loss of insecti- 

 cidal properties. 



Throughout the experiments of 1919 a study was made of the relative effects 

 of two applications as compared with one. The results indicated that an effi- 

 cient degree of repellent protection is better secured by a combination of 

 greater dilution applied twice than by a combination of less dilution applied 

 once. The average percentage of infestation on all check rows on radish in 

 1919 was approximately 70 per cent. The percentage of infestation in treated 

 rows using the tobacco dust diluted with lime ranged as low as 18 per cent. 



In the summer of 1919 preliminary studies were carried out in the insecticidal 

 properties of pyrethrum. The purpose of this was to throw some light on the 

 possibilities of this material with relation to control of root maggots. 



Published information as to the insecticidal qualities of pjTethrum is not 

 extensive. The substance has been used for many years and there is much 

 evidence of an inexact nature as to its efficiency in the control of certain insects. 

 The manner in which it may cause the death of an insect, or the possibility of 

 utilizing more eflficiently its insecticidal properties, has not been determined in 

 comprehensive investigations. 



The work in 1919 included in part ex-periments in the effect of pyrethrum on 

 plant lice. In these experiments the action of the material was that of a con- 



