PROCEEDINGS, 1918 11 



TABLE I. 

 Principal factors in control of lepidopterous insects. 



1. Not directly influenced by abundance of host. 



(a) Climate conditions; storms, floods, freezing, starva- 

 tion. 



(b) Predaceous birds. 



2. Influenced directly by abundance of host. 



A. Abundance usually dependent on climatic conditions. 



(a) Bacterial 



(b) fungi producing epidemic diseases. 



(c) protozoa) 



B. Abundance seldom dependent on climatic conditions. 



(a) predaceous mites and insects. 



(b) parasitic insects. 



Coming to parasites there are several different kinds, all 

 at times important from the point of view of natural control. 

 Many caterpillars are subject to epidemic diseases caused by 

 minute protozoa. Such for instance is the silk worm disease 

 studied so successfully by Pasteur. The Gipsy Moth and 

 many other insects are also subject to diseases of the flacherie 

 type that are perhaps protozoa and perhaps bacterial in origin. 

 Epidemics of fungous diseases also occur among larvae and some 

 times bring about a local extermination of their victi ns. Nema- 

 todes or thread worms also parasitize some insects, the best 

 known cases being perhaps the parasites of grasshoppers and 

 black fly larvae. Insect parasites are also commonly met 

 with in the control of most of our injurious and other insects; 

 those in my audience who have tried to rear moths or butter- 

 flies from larvae will know something of the value of these para- 

 sites. As I shall speak of these insect parasites later on I will 

 not dwell further upon them now. Finally, there are predaceous 

 animals that exact many pounds of flesh from the insect 

 world. The chief of these are birds and insects. The work 

 of birds has been admirably chronicled by Forbush, Weed and 

 Forbes and is now generally appreciated. To give a couple of 

 local examples: the Cecropia moth in New Brunswick is held in 

 check chiefly by the Downy and Hairy Woodpeckers that drill 



