1924 



ENTOMOLOGICAL SOCIETY 



85 



The butterfly emerges by splitting the chrysalid dorsally between the 

 lateral chitinous projections and along the mid-dorsal line forward to the head. 

 In two to three hours it is capable of active flight. 



Average Duration of Life Stages, 1923 



Stage 



1st Generation 



2nd Generation 



3rd Generation 



Egg Stage 



Larval Stage 



Chrysalid Stage 



Life to Adult life cycle 



Number of 2nd Individuals Reared . 



5 . 1 days 



18.0 days 



11.1 days 



34.2 days 

 23 



4.8 days 

 16.0 days 



9.0 days 

 29.8 days 



9 



6 . 1 days 

 26.5 days 

 Overwintering 

 Overwintering 

 13 



The maximum life of the butterflies in outside rearing cages was found to be 12 days, but 

 the majority of them lived only seven days. 



Artificial Control 



Control experiments, involving the treatment in three series of 5,000 early 

 and late cabbages, with Pyrethrum powder and lead and calcium arsenate dusts 

 and sprays, lead to the conviction that under local conditions dusting with lead 

 arsenate and hydrated or air-slaked lime in the proportion of one part to fifteen 

 parts is the most satisfactory form of treatment. The dusts were found more 

 satisfactory than the sprays in that they can be mixed and applied with the 

 aid or ordinary hand dusters, in one-fourth the time occupied in spraying. 

 They spread and adhere well if applied when the leaves are wet with dew, whereas 

 sprays to which soap has been added as a sticker have a low surface tension and 

 much of the liquid is lost in the soil. 



In these experiments calcium arsenate dusts gave less satisfactory results 

 than the arsenate of lead dust, the latter giving perfect control. Calcium 

 arsenate applied in the liquid form gave extremely poor results as well as causing 

 some burning to the foliage. Pyrethrum powder used with four times its weight 

 of hydrated lime proved satisfactory, but can hardly be used on a commercial 

 scale as it costs ten times as much as the arsenate of lead dust. 



Judging by this season's observations early market cabbages escape serious 

 injury and whether treatment is ordinarily necessary or not must be left to the 

 grower's discretion. For late cabbages and cauliflowers two applications should 

 be sufficient in a normal season, the first about the middle of July and the second 

 four or five weeks later. When the butterflies are very abundant a third applica- 

 tion may be necessary early in September. 



Natural Control 



Despite the fecundity of the cabbage butterfly and the favourable conditions 

 for its development presented by satisfactory climatic conditions and an abundant 

 food supply, its numbers fluctuate greatly from season to season. This is 

 largely due to important natural control factors which yearly account for large 

 numbers of the pest. 



Probably one of the most important of these is a larval disease known as 

 "flacherie," which is usually present to some extent every year, occasionally 

 occurring in epidemic form. Larvae affected with this disease turn muddy-gray 



