Insects And Humans

FIGURE 24.4. Summer transmission cycle of the western equine encephalomyelitis virus in the Central Valley of California. The mosquito, Culex tarsalis,is theprimary vector of thevirus, andhouse finches andhouse sparrows the primary amplifying hosts (hosts in which the virus multiplies). Secondary (less important) amplifying hosts include other passerine birds, chickens, and pheasants. Another transmission cycle involves blacktail jackrabbits, which are sometimes bitten by C. tarsalis, and Aedes melaniman. Humans and horses, as well as ground squirrels, tree squirrels, and some other wild mammals become infected but do not contribute significantly to virus amplification. [From J. L. Hardy, 1987, The ecology of western equine encephalomyelitis virus in the Central Valley of California, 1945-1985, Am. J. Trop. Med. Hyg. 37(Suppl.):18S-32S. By permission of the American Society of Tropical Medicine and Hygiene.]

hosts which compounds the problem of their eradication. With rare exceptions, for example, some myiasis-causing flies, insect parasites are not fatal to humans. In large numbers, insect parasites may generally weaken their hosts, making them more susceptible to the attacks of disease-causing organisms. Or the parasites, as a result of feeding, may cause irritation or sores which may then become infected.

But by far the greatest importance of insects that parasitize humans is their role as vectors of pathogenic microorganisms (including various "worms") some well-known examples of which are given in Table 24.1. The pathogen is picked up when a parasitic insect feeds and may or may not go through specific stages of its life cycle in the insect. Bacteria and viruses are directly transmitted to new hosts, an insect serving as a mechanical vector, whereas for protozoa, tapeworms and nematodes, an insect serves as an intermediate host in which an essential part of the parasites' life cycle occurs (Figure 24.4). In the latter arrangement the insect is known as a biological vector.

A pathogen may reside (and multiply) in alternate vertebrate hosts that are immune to or only mildly infected by it. For example, the bacterium Pasteurella pestis, which causes bubonic plague (Black Death), is endemic in wild rodent populations. However, in domestic rats and humans, to which it is transmitted by certain fleas, it is highly pathogenic. Similarly, in South America, yellow fever virus, transmitted by mosquitoes, is found in monkeys though these are immune to it. Such alternate hosts are thus important reservoirs of disease.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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