1924 ENTOMOLOGICAL SOCIETY 83 



At Ottawa there are three well-defined generations. The butterflies of the 

 first generation reach the height of their emergence before the middle of June; 

 those of the second appearing first in early July, increase rapidly in numbers 

 so that by the middle of the month they are common everywhere; the early 

 butterflies of the third generation mingle with the last of the second during the 

 middle of August, and continue to emerge until the end of September. It is 

 almost certain that no butterflies emerge from third generation pupae until the 

 following spring. 



Host Plants 



The host plants of the cabbage worm are not numerous, but represent four 

 plant families. The most favoured belong to the Cruciferae family, including 

 such crops as cabbage, cauliflower, radish and horse-radish. Cruciferous weeds 

 are sought after, especially in the spring, and the flowering plant Alyssum 

 maritimum, which is much used for garden borders, is also an occasional host. 

 The garden plants Cleome pungens and mignonette, of the families Capparidacecs 

 and Resedacece respectively, and the canary vine and nasturtium of the family, 

 Tropceolacece, are also attacked, but not to any serious extent. Larvae were 

 successfully reared on all these plants during this summer (1923) at Ottawa. 



Frequent mention has been made in literature of lettuce as a food plant 

 of the cabbage worm, but numerous attempts to induce the larvae to feed on it 

 at Ottawa in 1923 failed, and no lettuce showing signs of injury could be found, 

 although many of the plants were exposed to large numbers of butterflies 

 throughout the season. 



The Life of the Individual 



The male butterflies are found most commonly in the vicinity of flowers, 

 and the females in the neighbourhood of their favourite host plants. They are 

 conspicuous insects on account of the general colour of their wings, which is 

 white, finely powdered with yellow. The spring generation butterflies are 

 lighter in colour than those of the summer generation. 



The tips of the forewings are marked with black, the forewings of the 

 female in addition possessing two distinct black dots which readily distinguish 

 it from the male, which has only one. The wing expanse measures about one 

 and three-quarters of an inch, the female usually being slightly larger than the 

 male. 



Both sexes feed upon the nectar of flowers without which they cannot live. 

 The flowers of dandelion, Viola arvensis, radish, red clover, vetch and garden 

 stocks are the most favoured, but frequent visits are also made to pennycress, 

 field mustard, white sweet clover, burdock and Canada thistle, and to the 

 flowers of garden plants such as Erysimum, Scabious, Centranthus macrosiphon, 

 Clarkia, Hydrangea paniculata and cultivated sneezeweed. 



The flight of the butterflies is slow, irregular and usually low, but when 

 disturbed they can travel rapidly, and often rise thirty to forty feet from the 

 ground. 



Mating and egg laying occur within twenty-four hours after emergence. 

 While mating the male flits awkwardly from plant to plant, the female remaining 

 passive with wings folded. In depositing her eggs the female hovers on the 

 leaf for a moment, the tip of the abdomen being pressed firmly against the 

 surface of the leaf and withdrawn, leaving the egg adhering. The eggs are 

 deposited singly on any part of the plant above ground, but usually on the 



