REPORT OF THE SOCIETY 63 



by these wandering habits. It is probable that the small caterpillars, when 

 suspended on the silken thread, may be carried considerable distances by winds, 

 and the infestation still further extended in this way. When the caterpillar 

 becomes full grown, during July or early in August, it comes to rest, normally 

 upon the trunk or larger branches, but during an outbreak, upon any part of 

 the tree or upon neighbouring objects. Here it spins a greyish cocoon composed 

 of silk and hairs from the body firmly attached to the bark or to the object 

 upon which it rests, and within this it changes to the chrysalis or pupa. About 

 ten days or two weeks are passed in this condition, and then the adult moth 

 appears from the cocoon. The wingless female seldom moves away from the 

 cocoon out of which she has emerged; usually she crawls upon it, and after 

 being fertilized by a male and depositing there her whitish egg-mass, dies and 

 usually falls to the ground. The male caterpillars cease feeding and spin their 

 cocoons earlier than the females, and produce distinctly smaller chrysalids. 



There is only one brood annually in Quebec Province. 



The Injury. 



The extensive defoliation by the caterpillars destroys the beauty of the 

 trees for much of the season, and often injures them so seriously that branches 

 either die outright after repeated attack, or become so weakened thereby that 

 they gradually succumb to injury by other insects such as borers, and fungi. 



The list of trees attacked by the white-marked tussock includes a large 

 number of our deciduous shade trees, and even a few conifers. In Eastern 

 Canada the favourite food trees appear to be willow, birch, horse-chestnut, 

 basswood, elms, maples, poplars, and fruit trees. 



Natural Enemies. 



This species has a very large number of natural enemies. Minute hymen- 

 opterous parasites breed within and destroy the eggs, a large number of hymen- 

 opterous and dipterous parasites kill the caterpillars and pupse, and various 

 predaceous insects also aid in reducing their numbers. Certain fungi and bacteria 

 which spread rapidly in epidemics, destroy great numbers of the caterpillars, 

 and are sometimes a chief agent in their control. 



The last outbreak of the white-marked tussock in Eastern Canada, as 

 already mentioned, extended from Halifax to Western Ontario, and lasted, in 

 all, from 1903 to 1911. It was not anywhere abundant throughout the whole 

 period, however, and was brought finally and suddenly to a close by the action 

 of parasites and fungi. The species has bred in obscurity since that time, and is 



