Investigations by O'Roke, and others since, have shown the disease to be both prevalent and deadly. In the case of ducks the infection occurs discontinuously over a wide area where black flies are found: Adult birds are resistant to the disease, and the mortality is usually less than I percent. It is highly fatal to young birds, however, and mortality rates found by O'Roke were 10 to 100 percent. Individuals surviving the malady can carry the infection indefinitely; these "carrier" birds perpetuate the disease and serve as a source of new infection on the breeding grounds. Studies in areas of heavy black fly activity in Maine revealed that black ducks with an incidence of 89 percent probably were more prone to Leucocytozoan infection than were several other species including the wood duck, American merganser, hooded merganser, American golden-eye, and green-winged teal.

For a number of years an effort has been made through releases of game-farm propagated mallards to establish local breeding populations of the bird in New York State. The program has been mainly unsuccessful, and known mortalities from Leucocytozoan infection have provided a possible explanation of the failure. Losses of young mallards were known to occur in black fly areas successfully occupied by black and wood ducks, an observation which led E. L. Cheatum to theorize a possible explanation based on the following facts: The natural breeding areas of black and wood ducks are wood-margined water areas frequently in the immediate vicinity of black fly producing streams. Logically the long-time association with such habitats might through selective survival lead to a high degree of tolerance to Leucocytozoan disease for these species. Mallards, on the other hand, are primarily a plains species and their breeding territory probably has evolved through a geographic range relatively free of black fly vectors of this infection. Consequently, the mallard on its ancestral breeding ground has not been closely associated with the disease, and evolutionary opportunities for establishing characteristics of survival value have been lacking.

In addition to its fatal characteristics in some waterfowl, Leucocytozoan disease has been credited with being of importance to other species. In Canada, C. H. D. Clarke noted during 1932-1934 that the decline of ruffed grouse was associated with the dying off of young birds. Investigation revealed nearly a 100-percent incidence of infection with a species of Leucocytozoan newly described as L. bonasae. During another cyclic decline 10 years later, 60-70 percent of the adult birds examined carried this blood parasite.

THE RELATIONSHIP OF INSECTS TO WILDLIFE has scarcely progressed beyond the "check-list" stage. The types of insect and other arthropod pests that one might expect to find on any given species of bird or mammal are reasonably well known. Also, there is some understanding of the potentialities of many of these parasites as disseminators of disease. There is little information, however, on the incidence of insect parasites and the diseases they transmit. And there is little to show how the numbers of these fluctuate seasonally and with the condition and population density of the host. The significance of parasite relationships to the individual and to populations of the host is a complex subject only vaguely understood. Until more basic facts are available on such points it is futile to speculate on the type of management programs that might be effective in dealing with problems involving these pests.

In some instances further research may demonstrate a justification for local programs of insect control. Referring to Leucocytozoan disease in ducks, we recall that on some areas a very high incidence of the disease was accompanied by a nearly 100-percent mortality among the young. Present methods of black fly control are both selective and economical. The elimination of this link in transmission of the disease undoubtedly could be profitable in some areas of concentrated duck nesting.

Principally, however, insect influences on wildlife are not of a nature to justify or require such direct methods. It is the common circumstance for wild animals to support their ectoparasites with only minor inconvenience to themselves. And when through unusual numbers, or transmission of a disease, these pests are responsible for widespread losses to their host species, it is usually a reflection of a more basic cause. In this connection we might consider briefly the present plight of big game herds throughout most of the United States.

Every winter tens of thousands of deer die in 30 of the 48 States that support populations of deer. The perennial inquiries following such die-offs reveal excessive parasitism, both internal and external, along with evidences of various infections and deficiency diseases. Autopsy reports routinely ascribe a share of the victims to infestations of bot fly larvae or other such parasites, some to pneumonia and similar ailments, and a proper percentage to plain starvation. As many investigators point out, the important consideration, of course, is that while the ultimate cause of many of these losses is disease, excessive parasitism, or a combination of such factors, the basic predisposing condition is malnutrition resulting from inadequate winter range. Obviously the solution to this widespread problem lies not in finding an economical direct means of insect or disease control, but in creating conditions which will insure for the animals concerned the high level of general health known to be effective in providing resistance to diseases, and to both the numbers and effects of parasites.

On a limited and local scale some partial alleviation of such winter food shortages has been accomplished in the West through dispersing and "moving" game concentrations. By placing salt at summer range elevations in Montana, elk herds have been encouraged to remain later in the fall and to return earlier in the spring. This has reduced the demands on limited winter ranges, and allowed some recovery of forage plants, as well as holding the animals in areas of abundant food supply. Considering the over-all problem, this procedure is of only very limited utility and has no application in the principal problem areas of the Eastern States.

The solution that has long been recognized by biologists is to reduce herds and maintain them at densities consistent with the forage supply. This can be readily accomplished through liberalized hunting and the taking of deer of any sex and age. Unfortunately there has been no widespread understanding of the problem, and public sentiment has opposed and prevented the adoption of this conservation measure. The alternative, now being followed in most States, is for natural forces to accomplish the reduction but only with further deterioration of the range and a deplorable waste of game.

Among other important species of wildlife, intervals of marked prosperity are observed to alternate with periods of acute population depression. The basic factors underlying these cyclic trends are not known. But the build-up in numbers of the host is observed to be accompanied by a corresponding increase in populations of ectoparasites, as well as in the variety and numbers of other "lesser life." The increased prevalence of these parasitic and infectious agents quite certainly is an effect of high host populations. To what extent they ultimately may function as a direct or indirect cause of the decline is not known. A clear understanding of such relationships would have far-reaching value. Besides providing a firm basis for the sound management of game populations, it is likely that such fundamental knowledge would find application in the field of human epidemiology and in other branches of science dealing with animal numbers. From these standpoints the problem is one to justify the concerted and coordinated attention of scientists of many specialties and interests.

J. P. LINDUSKA, formerly assistant chief of the branch of wildlife research, and now chief of the branch of game management, United States Fish and Wildlife Service, is a graduate of the University of Montana and Michigan State College. Before joining the Fish and Wildlife Service in 1947, Dr. Linduska was employed as a wildlife biologist with the Michigan Department of Conservation, and as an entomologist with the Bureau of Entomology and Plant Quarantine.

ARTHUR W. LINDQUIST, a graduate of Kansas State College, has been an entomologist in the division of insects affecting man and animals, Bureau of Entomology and Plant Quarantine, since 1931. He has conducted and directed research on the biology and control of the screw-worm, blow flies, cattle grubs, horn flies, house flies, mosquitoes, tabanids, and other pests affecting livestock.

Deer fly.