50 THE EEPOET OF THE * No, 36 



Forest and Shade Trees. 



Canker "Worms (Alsophila pometaria and Paleacrita vernata). The preval- 

 ence of these worms has already been mentioned under orchard insects. 



Birch Leaf Skeletonizer (Bucculatrix canadensisella) . Last year the 

 work of this small caterpillar was very conspicuous in the Eastern part of the 

 province. This year it was conspicuous in forests between Gait and London 

 where in September the brown appearance of the birch foliage was very notice- 

 able. 



Oak Twig Pruner (Elaphidion villosum). In the Muskoka district .great 

 numbers of dead twigs and branches, killed by this insect, were everywhere to be 

 seen. 



Imported Poplar and Willow Curculio (Cryptorhynchus lapathi). This 

 destructive insect has now spread almost everywhere through the province and 

 has destroyed great numbers of native willows and poplars. 'Considerable damage 

 has also been 'done to Carolina poplars set out for shade or ornamental purposes. 



THE CABBAGE MAGGOT (Phorbia brassicae Bouche). 

 L. Caesar, Ontario Agricultural College, Guelph. 



This paper is a brief statement of some of the more interesting results 

 obtained from a study of the cabbage maggot during the four years, 1918 to 1921. 

 These are as follows: — 



There was no evidence to indicate that the insect winters in any other .way 

 than as a puparium in the soil or occasionally in the stumps of cabbage, cauli- 

 flower or other similar plants. 



Adults from these puparia begin to emerge in April or May and the 

 great majority are out by the end of May, a ,few, however, continue to emerge 

 over a long period — in 1918 up to the end of August, in 1919 and 1920 to the 

 middle of July and in 1921 to the 21st of June. Later broods have also a pro- 

 longed emergence period. 



The shortest preoviposition period in our cages was a little over four days. 

 Fifty per cent, of the flies that oviposited in the cages did so inside of six days. 

 There is considerable evidence to indicate that in the' field the preoviposition 

 period may be as short ; as two days. This would not be at all surprising since 

 we know that females can mature eggs at the rate of 20 1 or 30 a day. 



The largest number of eggs laid by any one fly was 117. These were deposited 

 on six different days over a period of nine days — June 1.7th to June 25th. 

 Another fly laid 103 eggs as follows:— May 28th, 51, May 29th, 29, May- 30th, 23. 

 Thus it is evident that bk^ laying rnay continue over a considerable period -find 

 that 20 or more eggs may be deposited each day. It would, therefore, not fee 

 surprising if at least some individuals laid 200 eggs or more. 



The length of life of the flies is apparently, as Schoene suggested, three .weeks 

 or more. In cages, situated in the north-east corner of pine woods males of the 

 first brood averaged 19.1 clays and of the second brood 16,6 clays: females, of the 

 first brood 22.7 -days and. oi the second brood 22 days. ->, r; 



No fly was in any case seen to lay eggs where these would- be exposed, to the 

 sunlight but always in. the shade. , ..,...,,..,., 



'". .The shortest, incubatiqn period, for the eggs was .slightly uncter 48 hours, 22 

 out of a total oi 475, or. 4.6 per cent. ^hatching in this' time. ',V In. 49J8. the average 



