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Arthropoda play a role in human welfare that is poorly understood by the general public. Most oceanic animal life is not the larger fishes and mammals, but tiny animals that make up the greater part of the plankton: the free-swimming, minute Crustacea on which other inhabitants rely for food. These free-living plant-feeding scavengers occur in vast numbers and interact with other animals to reduce the numbers of those that expire. Similarly the insects exhibit a more dominant role. Because of their large numbers and high adaptation for survival they outrank in abundance other animal or plant associations. It has been impossible to estimate the number of ants that populate fields and hillsides or the plant lice that derive sustenance from wild and cultivated plants. The role that insects play in agriculture and commerce is especially underestimated for the losses agriculture suffers from their destructive feeding. But for human welfare the insects especially are of paramount importance as they can regularly affect human's very existence or retard advances in the development of some of the earth's most fertile regions. Governments have fallen due to the ravages of diseases spread by arthropods. A notable example is the defeat of the British Army during the American Revolutionary War due to a widespread epidemic of malaria among the British troops. The Americans were able to rely heavily on the labors of the African population for food and supplies because they had a built in resistance to the disease from millennia of coexistence in Africa.
Medical entomology and parasitology are important academic fields for zoologists, physicians and the public. There is a constant need for more knowledge of the interrelations, which arthropods play in the spread, and maintenance of plant, animal, and human diseases. Insects especially have gradually made governments devote resources to long delayed studies. Some of the prominent early researchers in this field may be viewed at <Researchers>.
There are many important diseases associated with arthropods. Some of the more important ones include Malaria, Piroplasmosis, Trypanosomiasis, Yellow Fever, Plague, Dengue, Phlebotomus Disease, Spirochetal Diseases, Tsutsugamushi Disease, Kedani Fever, Flood Fever, Japanese River Fever, Rocky Mountain Spotted Fever, Typhus Fever, Tularemia, and Onchocerciasis.
It is important also to consider the mechanical movement of pathogenic organisms by insects, especially filth flies. Since early times ordinary people and physicians associated flies with disease outbreaks. An abundance of flies during summer was associated with an unhealthy autumn. There are also animal diseases other than those of man, where insects are involved and which influence human welfare. For example, insects play an important role as vectors of plant diseases thereby affecting the food supply. In the gut of many insects are found representatives of the protozoan family Trypanosomidae, with generic names Crithidia, Herpetomonas, Phytomonas, Leishmania, Leptomonas. The relationships of some of these forms to animal and plant diseases are known but the majority of them remain undetermined. The problem of isolating and culturing these forms, and of determining their relation to the insects, to other animals, and to plants is extremely difficult. However, progress has been accelerating with the development of DNA analyses, and we may expect more exact information in the future.
In the study of insect-borne disease, particularly one in which the insect serves as the definitive or intermediate host, certain important considerations are essential. Some of the more important features of the various factors involved are (1) the parasite or etiological agent; (2) the definitive host. and the definitive reservoirs or non-reservoirs; (3) the method of transmission; (4) the intermediate host and the intermediate reservoirs or no-reservoirs; (5) the method of transmission.
There is a lack of understanding, however, even of the better-known insect-borne diseases. For instance, in malaria is is apparent that the only definite host reservoirs are Anopheles spp. mosquitoes, but how long they can remain infected is still uncertain. The number of Anopheles species that can act and the conditions under which they may serve as definitive hosts are still not well known, though much progress has been made toward solving these problems. In yellow fever the parasitic agent is a virus; but the animal reservoirs been determined only since the late 1800's. Also, not all the mosquito transmitters have been recognized. Many problems of sleeping sickness remain unsolved. However, data on all known insect-borne diseases can be assembled and the numerous unsolved problems pointed out. The literature dealing with medical entomology, parasitology, and preventative medicine is vast, and bacteriology and veterinary medicine should be included,
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Legner, E. F.. 2000. Biological control of aquatic Diptera. p. 847-870. Contributions to a Manual of Palaearctic Diptera,
Vol. 1, Science Herald, Budapest. 978 p.