PROCEEDINGS, 1918 37 



NATURAL CONTROL INVESTIGATIONS IN BRITISH 

 COLUMBIA 



By John D. Tothill, B.S.A., 



In Charge of Natural Control Investigations, 

 Entomological Branch, Ottawa' 



The forest tent insect (Malacosoma disstria) has an egg mass of 

 approximately 200 eggs. In areas where it is maintaining about the 

 same numerical strength during a short term of years, it is obvious that 

 on an average only a single pair of moths can come to maturity from 

 each mass of eggs. This means, of course, that about 198 of the 200 

 eggs in each mass fail to do so. 



With the direction of Dr. C. Gordon Hewitt, the Dominion Entomol- 

 ogist, an investigation in the natural control of insects is being carried 

 on, and the writer is undertaking the study of the causes of this stupen- 

 dous mortality in the case of a very few of our common injurious insects. 



One of the chief causes of mortality, or causes of control, has proven 

 to be parasitism and predatism by other insects. Indeed, in the host 

 insects studied, insect foes have shown themselves to be the chief regu- 

 lators of control ; for unlike birds, inclement weather, and epidemics of 

 bacterial and fungus diseases, they increase and decrease with their 

 hosts. 



The importance of such insect predators and parasites in the control 

 of insect pests has been recognized for many years, and already some 

 very practical uses for them have been found. The citrus industry of 

 California owes its vigour to the introduction from Australia of a few 

 insignificant-looking lady beetles of the genus Vedalia and of a few even 

 more insignificant-looking Agromyzid flies. The most common eastern 

 parasite of the cabbage worm was brought here many years ago from 

 its home in Europe. Owing to the introduction of its chief insect 

 enemies the dreaded gypsy moth is now under infinitely better control 

 than it was ten years ago. By thus helping insect foes of insects to 

 cross such barriers as oceans, mountain ranges, and deserts, the dis- 

 turbed balance of nature has in many cases been re-established. Such 

 work has been carried on particularly by the State of Massachusetts in 

 co-operation with the Federal Entomological forces in the case of the 

 gypsy and brown tail moths, and by the State authorities of California 

 in the case of citrus insects. The Government Entomological Service 

 in Hawaii and entomologists independently employed by the Sugar 

 Planters' Association in the Hawaiian Island, have been very active in 

 similar work. 



In the progress of natural control investigations in Canada it seemed 

 probable that barriers within the limits of the Dominion were affecting 

 the distribution of parasitic and predacious enemies of insects having a 



