— 15 — 



Many other examples might be given but these will suffice to show that the 

 lethal factors in most of the cases are beyond man's control. 



Mr. Fetch informs n^e that the Squash bug (Atiasa tristis) was very 

 abundant about Hemmingford, some fifty miles south of Montreal, yet I have 

 never seen a live specimen on the Island of Montreal, where its food plant is very 

 abundant. I cannot give any satisfactory explanation for its presence in one case 

 and its absence in the other. 



It is very apparent that our knowledge of the real nature of the actions of 

 the various natural factors of insect control is wofully deficient. 



Mr. J. D. Tothill of the Dominion Entomological Laboratory, Fredericton. 

 N. B., has made some interesting studies of the control factors that operated in 

 1912-15 in New Brunswick on the Forest Caterpillar {Malacosonm disstria) and 

 the Fall Webworm (Hyphantria sp ), published in the Annual Report of 



the Entomological Society, Nova Scotia. 1918. 



A ground-beetle (Calo.soma sp.) feeding: on Caterpillars killed l)y a bacterial disease, 



cuiworm; below, a species of Carabus. 



(After Brehm) (After Washburn) 



His observations showed that on the average chicadees and mites destroyed 

 50 of the 200 eggs in the egg-mass of the Forest Caterpillar, egg parasites des- 

 troyed 15, starvation killed 67 of the first stage caterpillars, ants killed 51 cater- 

 pillars of the 2nd, 3rd, and 4th stages, and parasites killed 13 caterpillars and 3 

 pupae. On the average only 14 adults survived out of 2000 eggs laid the previous 

 season by 10 females. On the supposition that half of the survivors were females : 

 the reduction would be only 30 percent in spite of the very heavy mortality. 



In 1914, there was no starvation and no reduction by ants, consequently a 

 great increase in caterpillars occurred, and the egg masses were so numerous that 

 a scourge of caterpillars in 1915 was looked for, but a light frost occurred in 

 1915 during the first stage of the young caterpillars, with the result that 

 practically all of them were destroyed. In 1916, they were so rare that they could 

 not be found. 



Mr. Tothill's studies of the Fall Webworm for six years (1912-1917) show 

 that about 10 percent of the egg-ma';? of 300 do not hatch. In 1912. the parasites 



