ENTOMOLOGY 2040 SECTION XIV INSECTS AS VECTORS OF DISEASE

LEARNING OBJECTIVES OF SECTION

After completing this section students should be able to:

• List the four basic types of plant pathogens transmitted by insects and give an example of each one.

• Rank the four types of plant pathogens in terms of dependence upon insects as vectors.

• Describe the various ways that insects increase the survival and success of plant pathogens.

• Describe the differences between virus diseases in plants and the toxic effects of insect feeding (toxaemias).

• Describe the differences in circulative, non-circulative and stylet-borne virus transmission and explain why it is important to know how a virus is transmitted in considering control options.

• Give examples of arthropods (insects and others) that act as vectors of animal diseases, and the diseases that they transmit.

• Explain how arthropod borne diseases have influenced the course of history.

• Describe the symptoms of diseases like Malaria, Yellow Fever, Filariasis, River Blindness, Bubonic Plague, Typhus, Lyme Disease, Rocky Mountain Spotted Fever and Sleeping Sickness.

Terms: Vector, Virus, mycoplasma, toxaemia, stylet-borne, circulative, Rickettsia, Bubonic plague, Lyme Disease, Rocky Mountain Spotted Fever, Trypanosomiasis, Onchocerciasis, Encephalitis, Arboviruses, Elephantiasis, Malaria, Tsetse fly.

Disease transmission by insects.

    1. Plant pathogens. In order of dependence upon vectors: Fungi--bacteria--viruses--mycoplasmas.

        a. Fungi (most important plant pathogens).

        b. Bacteria.

            (1) Increase survival.

            (2) Dissemination.

            (3) Inoculation.

        c. Viruses (second most important pathogens).

            (1) Aphids.

            (2) Leaf hoppers.

        d. Mycoplasma-like organisms.

            (1) Most dependent on vectors.

    2. Animal pathogens.

        a. Vectors. Most vectors are blood feeders.

            (1) Diptera.

                • Mosquitoes.

                • Black flies.

                • Sand flies.

                • Tsetse flies.

            (2) Other insects.

                • Triatomid bugs.

                • Fleas.

                • Lice.

            (3) Other arthropods.

                • Ticks.

                • Mites.

        b. Diseases.

            (1) Malaria--protozoa, Plasmodium.

                  • Vector--Anopheles sp. (species varies with location).

            (2) Filariasis - elephantiasis.

                  • Non-lethal, traumatic symptoms.

                  • Vectors--many species, include Anopheles, Culex mosquitoes.

            (3) Yellow fever (one of arboviruses).

                  • Many vectors--especially Aedes sp.

                  • Other viruses include encephalitis, WEE, EEE, ST. LV.

            (4) Onchocerciasis (river blindness).

                  • Microfilaria-gradual infection, blindness, 20%, other--look old.

                  • Vector--black flies, Simulium sp.

            (5) Trypanosomiasis (sleeping sickness).

                  • Trypanosomas, cause, sleep, coma, death.

                  • Vector--Tsetse flies.

        c. Other vectors and primary diseases.

            (1) Fleas - Black Plague or Bubonic Plague (bacteria).

            (2) Lice - Typhus (Rickettsia).

            (3) Ticks - Lyme Disease (bacteria).

                  • Rocky mountain spotted fever (Rickettsia).

STUDY QUESTIONS

1. List the four plant pathogens in order of increasing dependence upon their respective insect vectors.

2. Why are stylet-borne viruses more difficult to control than those of the circulative-type?

3. Describe three ways that an insect vector might aid plant pathogen bacteria.

4. Most vectors of animal diseases are blood feeders. What is an example of one vector that is not a blood feeder?

5. One of the most notorious of the animal disease vectors is the Tsetse Fly. What disease does this fly vector? Why is it and the disease it transmits, so important?

6. Explain why infrequent visitors to areas where River Blindness is endemic, are not in danger of contracting the disease.

7. How has Malaria and its vector, influenced the history of Alabama?

8. What is the vector of Bubonic Plague? Where in the U.S. would you expect to find the disease (or would you?) ? How has this disease influenced the history of the world?

9. What is the vector of Lyme Disease? What are the symptoms of the disease? How can you avoid contracting this disease.

10. Equine encephalitis is a serious problem in Alabama. What is the vector of this disease and how can you reduce the chances of your horses, or you, contracting this disease?

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