1924 ENTOMOLOGICAL SOCIETY 75 



Degrees of Infestation in Infested Territory 



With the exception of a limited area in the centre of the infestation where 

 accurate records were made by Messrs. Crawford and Spencer, during the 

 investigational work, no special effort was attempted until last year to record 

 the actual degree of infestation in the older portions of the infested territory. 

 The work in this connection last season was carried on after the completion of 

 the border-scouting in late September. Observations were made at various 

 points in three concentric circles surrounding Union village, the centre of the 

 infestation. On account of the small staff available, and the fact that the corn 

 was then being cut, the records were taken from only one field at each locality. 

 An effort was made to locate the most heavily-infested field at each point and 

 the degree of infestation was obtained from 300 representative stalks together 

 with relating data regarding the history of the field. This method did not show 

 the average conditions but substantiated the original decision regarding the 

 centre of the outbreak and verified established opinions concerning the benefit 

 of late planting. 



In 1923 a definite system of recording the development of the infestation 

 was inaugurated with the intention of continuing the work for several seasons 

 to supply accurate information regarding the importance of the pest under the 

 varied soil and crop conditions which are encountered in the large territory 

 affected and to locate local outbreaks. Definite points in approximately the 

 same three circles as used last year were chosen and include the counties of Elgin 

 and Middlesex and the western parts of Oxford and Norfolk. In addition various 

 points in the counties of Essex, Huron, Perth, Oxford, Welland, and Lincoln 

 have been included in this season's records. 



The method of crop-handling and climatic conditions are apparently very 

 favourable for the corn borer in a large proportion of the infested territory. In 

 1920, the first year of discovery, accurate infestation records were taken from 

 only a small area, due to the late date investigational work was started. One 

 field near Port Stanley showed 99 per cent, of stalks infested. Ten miles west 

 the heaviest infestation to be found was one per cent., and beyond that the 

 degree diminished rapidly. The north and northeastern spread were somewhat 

 greater than the above, and New Sarum, about ten miles from Union, showed 

 approximately five per cent, stalk infestation. A marked increase occurred in 

 all sections in the central area in 1921 and as noted above, the infested territory 

 extended to sixty-five additional townships. 



In 1922, 100 per cent, stalk infestation was very common near the control 

 area, and in the records taken on the inner concentric circle, within a radius of 

 six to eight miles from Union, the per cent, stalk infestation varied from 10.6 

 per cent, on the northeast and 90.3 per cent, on the west to 100 per cent, on the 

 east. The second circle radiating about fifteen miles from Union, showed 

 degrees of infestation varying from 7 per cent, to 77 per cent., the highest occur- 

 ring on the west, in Dunwich township. The third circle, covering localities 

 within a radius of thirty miles of Union, showed infestations ranging from zero 

 to 6 per cent., the highest being on the west, in Aldborouth township. 



As stated previously, our 1923 records were obtained in a different manner 

 from those of 1922. It is possible that individual fields between the record points 

 would show a greater degree of infestation than any of those studied. Never- 

 theless the survey will represent as near as possible the average intensity of 

 infestation. This season's circle records cannot be compared accurately with 

 last year's, but they will serve as a basis for standard records in future seasons. 



