PIERINAE: PIERIS RAPAE. 1211 



the damage done in a single year (1869) in the vicinity of Quebec at 

 $240,000, and Mr Kitohie states tliat one farmer near Montreal lost in a sin- 

 gle season over 12,000 head of cabbages. In 1870, according to Mr. An- 

 gus, they destroyed the whole crop of cabbage and cauliflower in some places 

 about New York where the insect had appeared only the year before, but 

 parasites were seen the same season and in 1871 the butterflies were 

 less abundant. 



According to Forbes, the only insecticides to use with this insect which 

 have anv practical value are pyrcthrum and kerosene, and these can be used 

 in the field with good effect only before the plants have headed. 



Fnpation. In preparing for transformation the caterpillar spins a 

 flooring of silk on the spot it has chosen, most frequently the under sur- 

 face of some dead wood, like a fence paling, making it thickest at the 

 point where the attachments of the chrysalis are to be. It fastens a girth 

 around its body across the middle of the first abdominal segment, and so 

 snugly that its body is usually closely appressed to the surface. It 

 seems to prefer a surface as nearly horizontal as possible. The change to 

 chrysalis takes place in about twenty-four hours after the work is com- 

 pleted, and after the change the girth is found crossing the same segment. 

 The chrysalis, when not hanging for the winter, generally changes in about 

 ten or twelve days. 



Life history. This butterfly is triple-brooded in New England though 

 only double-brooded in Europe. It is a little earlier than its congeners, 

 appearing in the spring in Europe ten or twelve days before P. napi, and 

 in America about a week or less before P. oleracea. In the latitude of 

 Boston, the male appears shortly after the middle of April, sometimes not 

 until the 24th or 25th, and both sexes are very abundant early in May 

 and continue to fly for at least another month. By the second week in 

 June they become scarce, and after the middle of the month few are seen. 

 The butterflies pair not twelve hours out of chr3'salis, and the eggs are 

 laid through most of May and until the butterfly disappears ; they hatch 

 in eight days and the caterpillars require from two to three weeks to gain 

 their full size. The chrysalis hangs from eight to fourteen days and the 

 second brood of butterflies appears the last week of June ; it continues to 

 emerge from the chrysalis for fully a month and remains upon the wing 

 until the tliird brood makes its appearance, which in its turn flies until 

 nearly the middle of October ; so that with the exception of a week or ten 

 days in June, rarely prolonged to a fortnight, these butterflies are with 

 us from early spring to the time of severe frost. Owing to this the time 

 of the advent of the third brood is less marked, but its first members 

 arrive in the latter half of August ; caterpillars in nearly every stage and 

 chrysalids may be found throughout August and September and almost to 

 the end of October, when the last caterpillars transform to chrysalids and 

 hibernate in this condition. 



