CHAPTER XII 



INSECT TYPE PROBLEMS: CABBAGE BUTTEPvFLY 



{PONTIA RAPJE) 



Pontia rapct. This wliite butterfly commonly seen flitting 

 over garden and roadside, has long been a serious pest. It 

 gains its familiar name — cabbage butterfly — from I'avages of 

 the larva upon the Crudfer family, especially the cabbage. In 

 the northernmost portion of North America it is two-brooded, 

 in the latitude of New England three-brooded, and farther 

 south many-brooded. A butterfly lias been kno\^ai to contain 

 over 500 eggs, and the progeny of a pair of cabbage butterflies 

 in a season m the latitude of Boston is estimated as 31,375,500. 



The cabbage butterfly was accidentally introduced into 

 America from Europe hi 1860, and twenty-five years later it 

 had spread over nearly the lengtli and breadth of tlie land. 

 This rapid invasion was due to the fact that its natural enemy, 

 the ichneumon fly (^Apanteles glomeratns)^ was not present to 

 hold it in check. This insect, however, was introduced in 

 1883 and is increasing rapidly. The cabbage butterfly may be 

 collected in its different stages and the specimens kept in 

 breeding cages (Fig. 73) for study. Larv?e thrive well in the 

 laboratory if they are supplied with fresh cabbage leaves. 



Eggs and larvae. The small yellow eggs are deposited singly 

 on the undersurface of cabbage leaves. Keep in water m the 

 laboratory leaves upon which eggs have been deposited, noting 

 how long it takes the eggs to hatch. Measure the young larva 

 and note the time it requires to double in length. Does its 

 color match that of the leaf upon which it is feeding ? What 



is the advantage of this ? 



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