entomological knowledge. A single British college established in 1911 a fuller course of specialized training, and has since provided a four-year course, designed to teach not only ento- mology but also so much of allied subjects as to enable the entomologist to collaborate readily and intelligently with his colleagues in plant physiology, plant breeding, mycology, bac- teriology; it embraces some training in all these; it is divorced from zoology and the comparative anatomy of animals, except in so far as these are necessary to a wide comprehension of bio- logical questions, and it provides a full and complete training in all aspects of applied entomology; further, a feature is the inclusion of research on some problem of applied entomology as part of the actual training, so that the trained student has had some experience of the kind of problem he will spend his life solving. Progress in this direction was being slowly made up to 1921 at other teaching institutions in Great Britain, but it contrasted poorly with the progress made in the United States in the provision of full facilities for training at many colleges and experiment stations. The problem of economic entomology in England had been to escape from the dominion of the zoologist; the problem in America had been to incor- porate sufficient science and to escape the anti-academic demands of the " practical man," to whom science as such did not appeal. It is probably true to say that both countries err, the English in being still too academic, the Americans in being too practi- cal and too little sympathetic with the value of the " scientific " method of thought. This question was discussed at the Confer- ence of Agricultural Entomologists arranged by the Colonfel Office in England in June 1920, and while this Conference did not express any definite opinion, feeling was general that the ideal training was a groundwork of general horticultural or agricultural science, with the special training of the entomolo- gist thereafter, and this is very nearly a mean between the present training of the Imperial College in London and that of most of the American colleges. The total number of ento- mologists required for science in the British Empire was not in 1921 sufficient to justify the provision of facilities for training at a number of universities, and it was possible that the estab- lishment of tropical agricultural colleges might lessen the need of facilities in Great Britain, while providing better training for tropical problems. Careers in entomology had become far wider in 1921 than they were in 1900; in 1910 there was no official entomologist employed in England. The entomologist attached to the Ministry of Agriculture was in 1921 stationed at Harpenden, where he was in close touch with the Phyto- pathological Institute, with several entomologists employed upon research, and a beginning had been made with the appoint- ment of local entomologists, each to advise a small group of countries and to work on the staff of the institutes designed to assist the progress of agriculture and horticulture. There are entomologists attached to the departments of almost every British colony, and the Dominions of Canada and South Africa maintain larger departments with considerable staffs. India was in 1921 still provided only with a small number of ento- mologists attached to some of the provincial governments, and had a small teaching and publishing section, not directly con- cerned with the checking of insect pests, at the Agricultural Research Institute. The most complete economic entomology department in India was that of the Madras Government, but entomologists were attached also to the agricultural depart- ments of the Punjab, United Provinces, Bihar and Orissa, and Burma. A recent phase in the development of this subject is the increasing utilization of entomologists by companies engaged in the cultivation of tea, rubber, sugar-cane and similar prod- ucts, or by associations of such companies. The Indian Tea Assn., the United Planters' Assn. of South India, the Colonial Sugar Co., and similar organizations in Malaya, Fiji, Jamaica, etc., maintain scientific staffs usually with entomologists, and there are considerable developments probable, now that the commercial community is realizing that economic entomology can be a sound, practical affair, and not an amateur scientific business of naming insects. In the United States, the develop-
ment of entomology as a career for trained men has probably reached its limit; as the conditions of agriculture stabilize themselves, as the proportion of each crop becomes fixed, so the immense incidence of crop pests characteristic of America will diminish, and it is now probable that the main concern of the entomologist in that continent will be to safeguard the industry against the incursion of fresh pests from abroad. European countries have been developing very much as described above. Before the revolution in Russia, there had been an immense impetus to the development of entomology in that vast country; in France and Italy the entomologist is now being increasingly utilized, and while in Germany the subject had been neglected, since the war the Association of Economic Entomologists has stimulated the development of practical applied entomology. In Japan the development of the sub- ject has come with the increase in scientific departments, and especially with the immensely valuable results derived from research on the silkworm-rearing industry.
Control of Pests.- The principles on which it is sought to control and check insect outbreaks developed very markedly during 1910-20 from " artificial control " based upon direct remedies and insecticides, to " natural control " based upon an understanding of the factors that produce outbreaks of pests and action arising from that knowledge. The first essen- tial is a really intimate knowledge of the pest itself, its habits in all its stages, its senses and sense organs, its (almost) daily ways in the most minute particulars. It is now recognized that this must be carried to a degree of detail not contemplated before, and that upon the intimacy of this knowledge depends the successful application of any direct method. It is not sufficient to know that eggs are laid in such a way, in such num- ber, at such a time, that the larvae moult so many times, feed in such and such a way and pupate, that the pupa takes a cer- tain time, and then the adult emerges to mate, lays eggs and dies. An instance may be taken from the Codlin moth, whose larva hibernates in the winter in shelter; the full-grown larva leaves the fruit, crawls about, and for shelter will get under a flake of bark, spin a light cocoon and there remain. Will it do this on the trunk and branches, on the north (exposed) or the south (sunny) side, must the bark be dead or alive, will it pre- fer a band of bast, cotton, jute, wool, silk or what? Must this be double or single, tied on tightly or loosely, all round, at what height, when put on, when taken off? The investigator has to try to put himself as far as he can into the mentality of the insect, and the success of the entomologist depends much upon this instinct, which will yet be much developed. The second essential is a study of controls; what is it that, in its native habitat, checks the increase of the insect? Is it climate, food, plant scarcity, parasites, predaceous insects, birds, bats, lizards, frogs, etc., or disease due to fungi or bacteria? Usually it is direct parasites, predaceous insects, and perhaps, under suitable climatic conditions, disease due to fungi, bacteria or a virus. It is these natural checks which, in natural conditions, balance the rate of increase of the insect, which is large. The third essential is the nature of the conditions which produce an increase of the insect to such a point that it becomes a pest, that is, so injurious as to affect the crop yield materially. Nor- mally there is under undisturbed natural conditions a balance of life; the checks and the natural increase of the insect are so balanced, in nature, that the insect never increases to a point of being destructive. But under artificial conditions of culti- vation, man disturbs this balance; he clears land, disturbing the ratio of plant life; he interferes with the bird life particu- larly; he plants areas with crops, i.e. an unmixed plant area, which favours the increase of any insect capable of feeding upon that crop, since the parent insect has not to undergo a precarious hunt from plant to plant for the proper food plant for its young, but finds an unmixed block, thereby escaping many dangers. In addition, man introduces blocks of new crop plants, which have not acquired protection against indige- nous insects, and which are at once attacked, lacking the protec- tion they will in time develop. These are some of the factors
