106 THE CANADIAN ENTOMOLOGIST 



POPULAR AND PRACTICAL ENTOMOLOGY. 

 The Imported Currant Worm, 

 by l. caesar and g. garlick, 



Guelph, Ontario. 



Pteronus ribesii Scop. 



As nearly everybody who is at all familiar with currants and gooseberries 

 has seen the imported currant worm, no description of the insect referred to 

 will be necessary other than to state that it is the common bluish-green cater- 

 pillar with black head and numerous black spots on the body, commonly found 

 feeding upon the foliage of gooseberries and some kinds of currants. 



It is not our intention in this article to give a full account of the life-history 

 and habits of the insect, but rather to draw attention to some points of interest - 

 and value discovered in a study made by the junior author for the senior at 

 Burlington, Ontario, in the year 1919. 



Host Plants. — The first point of interest to which we would call attention 

 is that of host plants. In reading over the literature, especially books, on 

 Economic Entomology, one finds such statements as "The imported currant 

 worm feeds upon currants and gooseberries" without stating definitely whether 

 there are any exceptions, or "It feeds upon all kinds of currants and goose- 

 berries." Our experiments show that such statements are inaccurate, for in 

 no case have we been able to see any proof that it will feed upon black currant 

 foliage. In the field, we occasionally found eggs upon black currant leaves, 

 but in no case was there any sign of feeding. In cages, larvae could not be 

 forced by any means in our power to feed upon such foliage and further, the 

 adults could not even be induced to lay eggs upon black currant leaves, though 

 they readily laid upon the leaves of red currants. Moreover, growers informed 

 us that they had never seen any injury to black currants by this species. We 

 believe, therefore, that there is practically no doubt that black currants are 

 immune and that the host plants are red and white currants and gooseberries. 

 Whether there are any species of gooseberries immune or not, we have not yet 

 been able to discover. 



Time of appearance of adults in spring. — Before beginning our study 

 we supposed that adults never appeared until the leaves were fairly well ex- 

 panded, hence it was a surprise to find females present in large numbers in 

 April and laying eggs before the largest leaves were the size of a ten-cent piece, 

 and when the majority of the buds had just burst. 



Parthenogenesis. — By cage experiments it was discovered that eggs were 

 often laid by unmated females, and that these hatched just as well as fertilized 

 eggs; in fact, in the later broods the females avoided the males as far as possible 

 and appeared to lay more eggs when unmated. The adults derived from these 

 unfertilized eggs were, in every case, males. This shows, therefore, that though 

 mating is not necessary for the hatching of eggs, it is necessary for the perpetua- 

 tion of the race. 



Length of pre-oviposition period. — In the case of most of our common 

 insects, a period of several days elapses from the time the adults appear until 

 eggs are laid. The imported currant worm and several other allied saw-flies 

 are exceptions to this. In the case of the former insect, oviposition begins in a 



May, 1920 



