The high degree of host specificity of many phytophagous insects is a commonplace, yet remarkable phenomenon. Nevertheless it has been relatively neglected as a field for experimental study.

The first beginning was made about 50 years ago when Grevillius (1905) found that the larvae of the browntail moth Euproctis chrysorrhoea (L.) which feeds on the chick weed, Stellaria, could be induced to feed on other plants by smearing the leaves with a paste containing tannin which is a constituent of chick weed. It is un1ikely that this work was highly critical with respect to the chemical purity of the test preparations, yet the basic principle inherent in all experimentation in this field was employed. That is to say, a relatively isolated chemical constituent of the host plant together with some ingestible substrate other than the host plant tissue was offered to the insects. Obviously, the induction of feeding indicated that the test material contains some substance that stimulates the appetite of the insect.

Our present day concepts of the classification of insects are the result of a long period of development in the observations and thinking of the early naturalists, zoologists, and in more recent times, the more specialized entomologists. We are now so far removed from the original concepts on which the early classifications were based that many of us fail to realize that the systematic arrangement of animals, and particularly the invertebrates, was long a difficult and complicated problem which gave risk to much confusion. It may, therefore, be profitable as well as interesting to review the development of insect classification with respect to the ideas that have had a profound influence on the subject, and the men who have proposed these ideas and exerted the greatest influence. So, I propose to attempt to examine, evaluate and report to you some of the more important ideas and episodes in the development of this phase of insect taxonomy.

L'étude monographique de H. C. Fall (1922), “The North American species of Gyrinus”, a permis à de nombreux entomologistes de reconnaîrre assez facilement les Gyrins des territoires inventoriés par eux-mêmes et a facilité la mise en ordre des collections existantes. Nous en voyons la preuve dans les quelques additions ou listes qui parurent durant les dix années suivantes. Wallis (1926) décrit le Gyrinus dubius et le G. hatchi; il restaure le G. piceolus Blatchley qui avait été réduit au rang de synonyme par Fall. Chamberlain (1929) décrit le G. gehringi, provenant de l'état du New Hampshire. Brown (1928) donne une liste des espèces canadiennes. Il énumère vingt espèces pour la seule province de Québec, dont la plupart proviennent de la région de Hull ou de Covey Hill. Le Gyrinus opacus n'est cependant mentionné que pour la baie James. En 1931, Fall donne la description de Gyrinus instabilis dont le type et les paratypes proviennent de l'Alaska. Depuis, très peu de travaux semblent avoir été faits sur ce genre d'insectes, soit au Canada, soit aux Etats-Unis.

The eye-spotted bud moth, Spilonota ocellana (D. & S.), has a long history as a pest in Nova Scotia apple orchards, serious damage by it being reported as early as 1891 (Fletcher, 1892). Its status has fluctuated considerably, the most notable outbreak reaching its peak in 1927. This outbreak occurred when dusts were being used for the control of orchard pests, and (Kelsall 1932) was one of the two main reasons for abandoning the general use of dusts after 1927. The bud moth declined rapidly after 1927 and by 1931 was rated a minor pest (Gilliatt, 1932a). After flutuating at relatively low levels for seven years, it increased in importance and by 1942 was again a major pest. From 1942 to 1952, there was little change in its general status although large fluctuations in population were observed in orchards in which certain insecticides had been used (Stultz, 1950). During 1953, there was a marked decline in the average population level although reductions did not occur in all orchards.

Dryness of either an insect's habitat or its food has often been reported as inducing diapause. This has been well substantiated in Pectinophora (8, 21, 22) and Loxostege (23). Also, a difference in body moisture between forms of the same species, in diapause and not in diapause, has been recorded in Leptinotarsa (9), Lucilia (11), and Carpocapsa (24), there being less water in the insects in diapause. It is significant, though, that in preparing for diapause Leptinotarsa achieves a reduction in moisture content, even when there is an abundance of water outside, by excretion (4).

On September 21, 1953 the writer collected several egg capsules of the wood-roach, Parcoblatta pennsylvanica (DeGeer), from beneath the bark of dead, fallen trees in Rondeau Park, Kent County, Ontario. The capsules were put in a jar for rearing. During December 7 and 8, 1953 eight chalcidoid wasps, two males and six females, emerged from the capsules. They were identified as Systellogaster ovivora Gahan (family Pteromalidae) by Dr. 0. Peck, Systematic Entomology, Department of Agriculture, Ottawa, who pointed out that this was the first Canadian record of this genus. One male and three females from this collection are deposited in the Canadian National Collection.

In The Canadian Entomologist for January 1953 (pp. 19-30) the writer described the larval forms of Dichaetoneura leucoptera Johns. and discussed the relationship of the genus Dichaetoneura which was regarded by Johnson (1907) as closely related to Phytomyptera Rond. and later reduced to a synonym of this genus by Curran (1934). He pointed out that there are rather marked differences between the two genera in adult characters and expressed a doubt that Dichaetoneura could be classed with the Actiines as in the Manual of Myiology of Townsend (Manual of Myiology, IV.). He further remarked on the similarity between the adults of Phytomyptera and Schizactia noting briefly some of the larval characters of Schizotachina and Schizactia which are quite different from those of Dichaetoneura. In a later paper on Hyalomyodes triangulifera Loew (Can. Ent., Vol. LXXXVI, No. 3) he gave data on the larval forms of Schizotachina, Schizactia and Psalidopteryx.