Introgressive hybridization, the feeding back of alien genes from an invading species into a resident population, has not been widely studied in animals. Conclusions favouring its occurrence are mostly founded on comparative studies of external morphology: since parallel selection of similar gene allels would provide the same end result, such conclusions are open to question. White's arguments against introgression as the cause of overlapping phenotypes in Austroicetes grasshoppers, on the other hand, carry conviction because they are based on comparative internal morphology – on cytological study: the two supposedly interbreeding species were found to differ in several chromosomal diagnostics, to the complete absence of intermediates.

The development of the Manitoba Horse Fly Trap was motivated initially by the need to control tabanid flies in spite of a lack of effective and safe insecticides. This objective could be realized only through a study of orientation behaviour in the field. Starting with the old observation that tabanids are attracted to darkcoloured objects (‘targets’), the influence of colour of target, colour of background, size, shape and movement of target were investigated. The most attractive target proved to be a glossy black (or red) sphere about 24 inches diameter, about three feet above the ground. In the course of its development the trap has provided interesting insights into visual perception of tabanids which will require physiological confirmation. The attractant principle is overwhelmingly visual. An initial surmise that thermal radiation contributes to the attraction significantly has been superseded, although a thermal stimulus may be involved in the behaviour of the flies after they reach the trap. Since only the hemato- phagous sex (females) is attracted to the trap, the behaviour involved appears to be teleologically related to host seeking activity. On arrival at the trap the insects fly in the space around the target and eventually move upward into the no-return chamber at the apex. When the trap is used for fly control the apical chamber is not needed if the interior of the trap is treated with a powerful, residual insecticide. In addition to its potential uses in conjunction with insecticides for control of tabanids, the Manitoba Horse Fly Trap can be used to study the correlation of flight activity with meteorological conditions as well as the seasonal and geographical distribution of tabanid species. The trap can be used effectively in the study of Stomoxys behaviour and control. If the sphere is replaced by a wick containing organic sulfides, blow flies can be attracted to it in considerable numbers.

During the past 100 years, insect control has been a predominant objective and influence on the development of entomology in Canada. Preoccupation with the insecticide method of insect control threatened for a while to divert entomologists from the biological bases of their science. But the scientific questions and practical problems raised by insecticides have recently generated a renaissance of biological thinking about insects and ways to control them. Older biological methods and certain promising new ones are receiving increased attention. Insecticides have won a permanent place in our arsenal but we can no longer continue to rely so heavily on this one weapon. A new perspective is emerging in which strategies of insect control will be formulated on the basis of population dynamics studies and will involve assembling from a variety of control methods the appropriate combinations to meet particular problems. The requirements of these combined strategies will impinge increasingly on economic and social affairs which, in turn, will modify the technology of insect control.

Chlorinated hydrocarbon insecticides and notably DDT have provided means of effectively controlling mosquitoes, blackflies and insects of medical importance not only in Canada but elsewhere, and of eradicating the transmission of malaria by anophelines, the world programme for which is already successfully half completed. However resistance has developed to these insecticides in 80 species of public-health importance, including 3 in Canada. Basic studies on the physiological mechanism and mode of inheritance of resistance in Culicine mosquitoes are being performed in Canada. Among insects and mites of agricultural importance, 14 species have developed resistance in Canada, and a world total of 77. Basic studies on the mode of inheritance of cyclodiene-resistance in root maggots are being undertaken in Canada. Countermeasures against resistance include the use of synergists, non-detoxicatable analogues, and negatively-correlated compounds. Resistance usually dictates a shift from the chlorinated-hydrocarbon to the organophosphorus insectices, thus reducing the residue problem, particularly for wildlife. Alternative methods of control include the sterile-male technique, with 2 successful examples but no success yet with mosquitoes, and the use of chemosterilants, with an example of imminent success against houseflies on islands. Chemosterilants however, like bacterial toxins, are not free from the possible development of resistance by detoxication.

The background against which decisions on control strategy and tactics are made is explained and general approaches to pest control are discussed at length. Canadian work on population dynamics that involves research on the processes that regulate numbers is reviewed. The author's conviction that this work provides the best avenue yet explored to the solution rather than temporary alleviation of pest problems is explained. A pest-control strategy for the insects attacking peach in the Niagara Peninsula, in which a logical progression of research, the assignment of priorities, and the concentration of staff and facilities on problems of major importance are advocated, is outlined. Finally, weaknesses in administrative strategy are discussed and it is suggested that the findings of basic researchers on population dynamics should be exploited more fully by parent organizations and applied more energetically by those directly charged with responsibility for insect control.

A computer program has been developed for use in evaluating various strategies of insect pest control. At its present stage of development, the program simulates the effects of various dosages of insecticide, parasite release, and spraying of virus, or any combination of these, weather and pest density on reproduction, dispersal and mortality in a pest population. Effects of changing pest densities on the parasite population and on tree growth and mortality in a hypothetical, 6.4 million-acre balsam fir forest are simulated. Also, the computer simulates dispersal of parasites and disease incidence. All computations are performed separately for each of 625 4-mile-by-4-milc hypothetical squares of forest area in the hypothetical 10,000 square mile area. All operating costs and losses due to lost tree growth and tree mortality are printed each year. The particular set of strategies to be used in each game is included in the input data for each 35-year computer experiment, along with data on physiological parameters, allowable pest thresholds for each type of control, genetic parameters, behavioristic and dispersal data and costs of control. One play of the game takes 50-120 seconds on an IBM 7090 computer, depending on the array of strategies selected.

There were a number of significant conclusions from the simulation study. Biological control agents can not be as effective as insecticides unless they keep the pest at very low levels indefinitely. If they only drop the pest to about 10% of the peak level it would have attained without control, this may not be good enough to save the trees, because lethal effects accumulate. That is, pest densities which are not quite high enough to kill a tree quickly can kill it if the pest persists at these densities for several consecutive years. However, by selecting biological control agents with optimal physiological parameters, biological control can be made to produce totally effective control.

For all kinds of control, control is vastly more effective if applied 10 years or more before peak pest densities. Therefore, potential pests should be subjected to preventive control at pre-pest densities, rather than being allowed to reach critical densities. The latter policy ignores the hazard of successive years of sublethal pest densities whose effects can cumulate to become lethal. It should be noted, however, that this conclusion follows from exploration of a hypothetical situation, and might not be applicable when considered relative to the exigencies of an actual field problem.

The decision-making process in insect control at the practical level involves not only the complex relationships between pests and their environment, but also equally complex human relationships and values. The actions advantageous to one of our resources may be harmful to another. Ultimately, the process of decision-making, at the individual problem level, must be integrated with economic factors, public health and sociological considerations. Calculated risks must be taken, but decision-making should he based on the evaluation of data bearing on efficiency, economy and safety of use of any method, including pesticides. Integrated control as a newly repopularized concept is examined in relation to the economics of its potential application in Canada. The concept of safety of pesticide residues in food is discussed and related to “good agricultural practices.” Three operative levels of decision-making are examined; the regulatory, quarantine and pest suppression activities and the role of the local advisory committees on pest control. The author expresses concern that the current public preoccupation with establishing safeguards for pesticide use does not begin and end merely with legislative action and strengthening of enforcement agencies. A desirable parallel result likely to be overlooked would be administrative and financial support for research on how the use of pesticides may be developed in the best interests of the community as a whole.

The Canadian program in insect pathology is reviewed in general terms. The pathogens that have been studied include viruses, fungi, bacteria, protozoans and nematodes. Many aspects of the various host-parasite relationships have been investigated under field and laboratory conditions.

Some recent developments on aphid digestive enzymes, aphid feeding and nutrition on host-plants, and on artificial media are briefly reviewed. A chemically defined diet, on which pea aphid life and reproduction can be sustained during two successive generations, is described. An important feature of this successful chemical diet concerns its amino acid composition, which was based on that of pea aphid blood and honeydew. An artificial feeding method for aphids divorced from their host-plants should prove a valuable tool in the study of the nutritional requirements and the intermediary metabolism of these insects, as well as in determining the influence of dietary constituents on polymorphism and in relation to the phenomena of plant resistance to aphids.

The number and kinds of courses in Entomology at Canadian Universities are briefly described. There is a discussion of two approaches to the undergraduate degree: one, the broad approach, where only one course in a specialty is taught but many disciplines are covered, and two, the narrower approach, where many courses in the specialty are given.

The author favours the broad approach. Biologists should be produced first and Entomologists second. There is some question as to whether, at the Universities, Entomologists, in the narrow sense, should be produced at all.

The argument for graduate training in biological disciplines instead of training in specialized groups of animals is presented. Also the question is raised of where, and how, graduate training should be done. It is concluded that graduate training is best done in the biological disciplines, that it should be directed by the Universities, not by off-campus laboratories and that it should be done in a manner decided by the Universities.

The reason control measures are applied is to reduce the harm caused by pests. “Pests” is a subjective word that is arbitrarily used to refer to some of the living organisms that harm man and his property. Pest control measures may be classified on any of several bases, bur any one classification that uses several bases is liable to cause misunderstandings. Biological controls are the use by man of living organisms to control pest damage. Approaches to biological control are illustrated by results of work on four pests found in Ontario. These results also illustrate how insects may be interrelated through natural enemies that they have in common. As far as possible control measures should be selective for pests, or pest and other non-beneficial, species only. Biological controls tend to be relatively more selective than other, comparable, control measures. They are also the most feasible existing way of keeping pest damage down without continuing human intervention. Increasing attempts to erase pest problems, rather than to alleviate pest attacks temporarily, may result in increased Government participation in and regulation of pest control programmes.

In aquatic insects, emergence (ecdysis to the adult or subimaginal stage) varies widely in temporal pattern. The comparative study of this pattern is feasible and informative in orders such as Plecoptera, Ephemeroptera, Odonata, Diptera and Trichoptera in which all members of a population pass through the water-surface when emerging. Methods by which emergence rate can be measured are discussed. Four basic temporal patterns of emergence exist. Emergence may be (1) continuous with irregular fluctuations in rate; (2) rhythmic, with a lunar period; (3) sporadic, occurring at irregular intervals of a few days; or (4) seasonal. Examples of each of these patterns are given, and reference is made to the proximate and ultimate environmental factors which may be maintaining the patterns observed. Diurnal rhythms of emergence are excluded from consideration. When emergence is restricted seasonally in temperate latitudes, the degree of its synchronization within the emergence period varies widely but is usually constant and typical for a given species. This has provided the basis for an ecological classification of British Odonata, the validity of which is examined in the light of recent research.

The first part of this paper discusses the characteristics of the arctic environment as it influences insect life. The most important features are the low temperature, the low annual heat budget, the severe and often variable weather and the continuous daylight of the growing season. A certain uniformity in aspect of the tundra environment is mentioned. Some microclimatic and regional differences are considered and a definition of the low arctic life zone is proposed.

The make-up of the arctic fauna is considered in the second section. In the low arctic there may be up to 5% of the number of species found in a comparable temperate area, and in the Queen Elizabeth Islands about 1%; but the representation of the various groups of insects in the arctic varies greatly, the Diptera, and especially the Chironomidae, being by far the most numerous. The fauna is derived from that of the north temperate zones, by extensive reduction and by a limited development of endemic forms up to, but rarely beyond, the specific level. Many of the endemic forms seem to be adaptations to the special features of the environment, especially the low temperature and short season; while others appear to show a loss of specialized features, e.g. of colour or pattern, in relation to the small number of species in their environment and the consequent lower level of biotic interactions. The arctic Lepidoptera are frequently cited in these sections and a number of species are figured.

The paper concludes with a discussion of the general reasons why so few species are found in the arctic. The arctic environment is not inherently simple and does not forbid a greater diversity, yet in fact very few species occur. It seems to lie beyond the range of physiological tolerance of all but a very few of the forms of temperate origin. But, given time, there is no apparent reason why a greater diversity should not develop, although the evolutionary process is probably slower in the arctic and is always liable to be set back by climatic disasters, from the last of which the fauna has only just begun to recover. It is suggested however that the arctic will always tend to lie towards the limit of the physiologically possible range because in fact the greatest continuity of evolutionary history has been in the tropics and most forms of life have thus been shaped in response to tropical conditions.

The underlying causes of grasshopper outbreaks in Western Canada are of interest both as an academic problem in insect population dynamics and as a practical problem in modern agriculture. Grasshopper populations reach their annual low point in early July when they are in the adult stage and increase sharply in the fall at the time of oviposition. Any factor that influences the grasshoppers during this period may have a marked effect on the outbreak of the following year. The relationship between grasshopper population numbers and proceeding fall temperatures may either control grasshopper populations directly by affecting their physiology or indirectly by affecting their parasites, predators, and diseases. Studies at the University of Saskatchewan aimed at solving this problem include investigation of the microclimate to which grasshoppers are subjected under field conditions, a survey of their feeding habits as shown by crop analyses, and a study of their oviposition behaviour. On the basis of available information an attempt is being made to predict future outbreaks at least 6 months in advance.

The functional morphology of the insect compound eye is reviewed with special reference to its surface and volume relationships with the rest of the head and its evolutionary development. Measurements of the more important parameters of the eyes of 28 species representing 14 major orders are given and interpreted in relation to this review. Recent histological and biophysical work on insect vision is also reviewed and some conclusions, especially those concerning the limit of sensitivity in the ultra-violet, are shown to be consistent with current theories of the early history of the oceans, the atmosphere, and of life.

Population ecology requires realistic and precise analyses of whole systems, or processes, and not just fragments of them. This poses some difficult problems because of the distinctive complexity of these processes. Recent studies of predation have shown, however, that it is possible to achieve great analytical depth and to simulate whole systems in the form of realistic and precise mathematical models. This is accomplished by ignoring the degree of simplicity traditionally required of population models and by emphasizing the need for reality. Extensive experimentation is required to suggest and test possible explanations for the action of each component of the process so that the explanation evolves in gradual steps to include one component after another. The form of the explanation and the resulting equations is hence dictated by the process itself and not by the need for mathematical neatness. The considerable complexity of the predation model arose from features common to many biological processes i.e. the prevalence of limits and thresholds, the presence of important discontinuities and the historical character of biological events. These features can be analyzed effectively only by establishing an intimate feed-back between experiment and theory. Mathematical models incorporating these features are admirably solved using digital computers. Computers, and the languages used to program them, seem to be ideally suited to handle the distinctive type of complexity shown by population processes.

A knowledge of ecological principles is essential to the successful development of future research on pest control problems in Canadian orchard entomology. Such knowledge should be especially helpful in spotlighting omissions in past studies as well as indicating new areas of study in the future. In particular, the ecosystem concept should serve not only as a basis for evaluating and bringing together existing data but also as a guide in the collection, integration and interpretation of new data.

Our approach should be to study the population dynamics of major arthropod pests in Canadian apple orchards to obtain data of the fundamental kind on natural populations of these species. Since this approach is dependent on precise measurement of the population and its mortality factors, as well as on the mathematical modelling of the data obtained, unambiguous deduction and greater understanding and utilization of the results would then be possible.

Examples from a recent eight-year study of the population dynamics of two pest species in Canadian apple orchards reveal that the fundamental approach to pest problems in Canada is both feasible and practical, and that the results can yield considerable insight into the role of mortality factors in population regulation as well as in control of pest stages of economic importance.

Three different types of historical population data on the fall webworm, Hyphantria cunea Drury, are examined graphically. Oscillations in population density have peaks at intervals varying from 8 to 16 years, and are generally synchronous over very large areas in eastern and central Canada. Temperature in late summer is a key factor affecting the rate of change in density, particularly during the development of gradations, and this explains the synchronism of the oscillations. Climate and vegetation appear to be the main factors determining differences in mean density from one area to another. However, oscillations about the mean density have discrete limits, which are usually below the limits imposed by the food supply even where climate is generally favorable, and population decline often occurs despite favorable weather. These limits are imposed by other factors, such as the parasite Campoplex validus Cress. which has a delayed response to webworm density in eastern Canada.

It is concluded that similar analyses for other insects, perhaps based on the sort of data being accumulated each year by the Forest Insect Survey, would contribute to the development of population principles and would suggest many useful short-cuts when more intensive work is undertaken on additional species.

Among the purposes of classification are association and relocation of data, expression of degrees of similarity, prediction of unobserved data, and expression of functional relationships. Classification must conform to the characteristics of the organism classified and also to the thought processes of the classifier. Analysis reveals hidden patterns and acts as a check on intuition, which though valuable is of uneven reliability.

The Linnaean system is well adapted to modern needs, though we have had to modify its theoretical basis. Modern information may force us to a fundamentally different system at levels at and below that of the Linnaean species.The data of conventional taxonomy are voluminous, but the obvious need for using more characters greatly increases the problem of recording and processing information. All characters, morphological or otherwise, of a species have potential taxonomic value. The latter are often less convenient but may yield special information.

Functional relationships must be distinguished from non-morphological characters. There is a problem of harmonizing classifications based on functional relationships with those based on similarity and difference of attributes. This problem takes different forms at the species level and at the level of higher categories.

The strategy of systematic investigation is influenced by the purpose. For identification a simple array of characters, in a dichotomous table, may be adequate. Such tables are well adapted to digital-computer operations. Where large arrays of characters are to be studied, as where functional relationships, variation or capabilities of organisms are important, time becomes critical, and priority should be given to characters that can be observed quickly or that are known to be specially informative. Methods of multivariate analysis are being applied increasingly in systematics. Methods using unweighted arrays of homologous characters are likely to be supplanted by those that permit controlled weighting, use of nonhomologous characters, and incorporation of sequential and functional relationships. Electronic computers will permit study of problems that would formerly have been too large or complicated. Trained observers will have to provide data, but special types of information, such as chromatograms, electrophoretic and serological observations, and biogeographic data, might be read automatically into a computer. With increased complexity and automation of computer operation, sound initial planning and checking will become more important. The whole subject of systematist-computer relationships needs experience, careful thought, and perhaps a reorientation of attitudes.

Systematics is an approach to biology rather than a department of it; it is intimately related to evolutionary genetic studies, and is in this generation uniting with them in a general science of population biology. Perhaps in the next generation population biology and individual biology will be united in an integrated body of biological science.

After defining the entomological use of the term mycetome a short general account is given of the various supposedly beneficial relationships between insects and internally harboured micro-organisms and the metabolic balance needed. Not all beneficial micro-organisms are harboured in mycetomes or even in mycetocytes, but the present paper is concerned only with insects having mycetomes. It is shown that there is good evidence for accepting the premise that true micro-organisms are found in insect mycetomes and that the micro-organisms supply the insect host with some useful metabolite (s), Special consideration is given to the genus Sitophilus, Here the mycetomal micro-organisms probably supply a useful nutrient that is "essential" only when the diet available to the weevils is inadequate. Whole wheat grain appears to be an adequate diet. Some strains of weevils apparently free of mycetomal micro-organisms are pale in colour, light in weight and particularly susceptible to dietary changes. Weevils reared at temperatures too much above the optimum lose their mycetomal micro-organisms. Although the organisms are pleomorphic there is evidence that their morphology in any one strain of weevil, reared under standard conditions, is constant: and thus it seems the micro-organisms may have taxonomic value in entomology. The possible origin of mycetomes and of the mutualistic associations are discussed and suggestions made about future research.