82 THE REPORT OF THE No. 33 



Keeping in mind that throughout the period the infestation in the immedi- 

 ately surrounding territory has been in general steadily increasing, there is 

 little doubt that the control measures have had a very definite effect and have 

 caused a material reduction of losses in the area under study. This was in 

 spite of the fact that the area was relatively very small and was surrounded by 

 country with heavy infestation in which little or nothing of a systematic nature 

 was done to reduce the number of larvae. 



The results attained to date leave no doubt that in any year the wide- 

 spread practice of the published control would reduce the European corn borer 

 population to a point where field corn would be grown with practically no loss. 

 And were these measures practised for three or four years the planting date of 

 May 24th or earlier could again serve as the standard and early sweet corn in 

 the most severely infested areas could probably be grown once more as a reason- 

 ably profitable enterprise. Sweet corn for the early market, on the other hand, 

 will suffer severe losses for years after field corn can be grown free from appreci- 

 able loss. 



STUDIES IN THE LIFE-HISTORY, BIONOMICS, AND CONTROL OF 

 THE CABBAGE WORM IN ONTARIO 



C. R. Twinn, Entomological Branch, Department of Agriculture, 



Ottawa 



The cabbage white or imported cabbage butterfly, Pieris rapes, L., was 

 first taken in Canada in 1860 in the vicinity of Quebec by Mr. William Couper. 

 Its subsequent spread south and west throughout the North American continent 

 was surprisingly rapid, its first appearance being recorded in the United States 

 in 1865, at Norway in the State of Maine. 1 



Before the advent of arsenicals as a popular method of controlling leaf- 

 eating insects, the cabbage worm caused considerable losses. Even now, when 

 spraying and dusting of cruciferous crops is so general, and despite the usual 

 high mortality among the larvae due to natural factors, the damage is by no 

 means inconsiderable. 



During seasons when the cabbage butterflies are very numerous the late 

 varieties of cabbage and cauliflower may suffer considerably, large irregular 

 holes being eaten out of the leaves, which in addition become scattered with 

 masses of dark green excrement. The larvae also have a tendency to concentrate 

 on the tender leaves forming the "head," often making the latter quite unfit 

 for market. 



Chittenden 2 estimated in 1916 that at least one-tenth of the entire cabbage 

 crop of the United States was annually destroyed by the cabbage worm, and 

 this statement would probably apply equally well to Canada. 



Seasonal History 



In Ontario the butterflies may be seen on the wing from the latter part of 

 May until the end of September. In 1923 none were seen until May 24th, 

 when they suddenly became common. During July, August and early Septem- 

 ber they were extremely abundant in the vicinity of Ottawa, on one or two 

 occasions several hundreds being counted at one time over a single acre of 

 cabbages. 



