DIVISIOX OF ENTOMOLOGY 861 



SESSIONAL PAPER No. 16 



Entomological Field Laboratory at Fredericton, N.B., the detailed study which he 

 is making on the natural control of the Forest Tent Caterpillar (Malacosoma 

 disstria) and the Fall Webworm (Hyphantria cunea). Observations were also made 

 on the parasites of the Spruce Budworm {Harmologa fumiferana) in Xew Brunswick. 

 Such an intensive study as is being undertaken is necessary- in order to ascertain the 

 manner in which the natural control of certain of our more common insect pests is 

 brought about and mr.intained, and the conditions governing the same. Until we 

 have such information our attempts to imitate or assist the natural control of 

 insect pests cannot be undertaken on the sound scientific basis which success 

 demands. No one can foretell to what practical uses it may not be possible to pvit 

 the results of knowledge so gained. Among the important questions involved is 

 whether in all cases a complete sequence of parasites is required. !No one species of 

 parasite can secure the natural control of the insect. Natural control involves 

 the destruction of a greater number of individuals of the species than are produced 

 by unrestricted incrtase. This destruction is brought about by numerous causes, 

 the chief of which are parasitic and predaeeous insects. Other causes are diseases 

 caused by micro-organisms of a bacterial and protozoal nature, fungi, or physio- 

 logical troubles. Usually, the parasitic insects form a sequence, ditferent species 

 of parasites attacking the insects in the different stages of its development. Some 

 attack the egg, others the young larvae or older larvae, and other species attack the 

 pupating larvae or pupae. These facts will indicate, perhaps, the complexity of the 

 problem and the nature of the information necessary for its solution or understand- 

 ing. 



Egg masses of Malacosoma dissiria were collected in different localities in New 

 Brunswick, Quebec, and Ontario, and four species of egg. parasites were reared and 

 studied. One of these species, known as No. 4, is evidently an important factor in 

 the natural control of the insect. It is an obligate parasite; the highest percentage of 

 parasitism for a locality was 9-85 per cent., but individual e^S masses were parasitized 

 sometimes to the extent of 50 per cent. 



In the study of the parasitism of Hyphantria, many thousands of caterpillars col- 

 lected from different localities were fed and dissected for larval parasites, and the 

 percentages of parasites from different localities were obtained by dissection, and rear- 

 ing. These parasites were mainly Apanteles, Meteorus, Limnerium validum, L. pilo- 

 sulnm, Varichoeia aldrichi Towns., and Exochilmn mundum Say. 



Mr. Tothill also studied the habits of the native ant Formica ulkei Emery, 

 which, together with other ants, may exercise an apprecia.ble influence in the natural 

 control of certain species of lepidoptera upon which they prey. 



II. INSECTS AFFECTING CEREALS AND FIELD CROP>. 



Cutworms. 



In view of the remarkable abundance of these caterpillars in southern Alberta, a 

 brief account of which I included in my last report, much information has since been 

 gathered on the life-history, habits, etc., of the species mainly responsible for the 

 dam.age, viz., Porosagrotis orthogonia Morr. (referred to in previous publications of 

 the Division as Porosagrotis delorata Sm.). In April last (1913) Mr. Arthur Gifcson 

 visited Alberta and made a thorough investigation of the infested districts. In com- 

 pany with Mr. E. H. Strickland, the resident Field Officer of the Division, he found the 

 cutworms fairly numerous throughout the Lethbridge district. They were particu- 

 larly present in fields of spring wheat, fall wheat, and oats. In some places, as for 

 instance at Iron Springs, Alta., they were present in certain fields in numbers varying 

 from three to eleven to the square foot. A series of control experiments was started 

 early in May. Infested fields were divided into various sized plots (none smaller 



16—56 Ottawa. 



