Hostinsect Interactions

There are several evident morphological adaptations for a blood-sucking life. Piercing or cutting mouthparts are the clearest example. In addition, many periodic and permanent ectoparasites such as fleas and lice are laterally or dorsoventrally flattened and are wingless, which are adaptations allowing them to move easily through the pelage or feathers and to avoid being groomed by permitting them to flatten themselves against the skin. Most of these ectoparasites also have cuticular extensions in the form of spines and combs. These are longer and spinier in bird-infesting forms than in those found on mammals. The combs in particular are found covering weak spots in the body such as the articulations between body segments. The spacing of the tips of the combs correlates well with the diameter of the hairs on the body of the host. This suggests that these combs have a dual function: protecting the body from abrasion and acting as an anchoring device for the ectoparasite.

The host regulates the numbers of permanent ectoparasites by grooming, usually with both the toes and the teeth. This often limits ectoparasite distribution on the host to those areas the host can groom least efficiently, such as the head and neck. The immune response mounted against these bloodsucking insects is often very localized. It makes feeding on these protected areas of the skin difficult, with the result that the insects feed less well or move to less affected areas of the body where they are more easily groomed. The result is that the host regulates ectoparasite numbers.

The host also shows behavioral defenses to temporary ectoparasites such as mosquitoes. The level of defensive behavior is usually density dependent and thus can have important consequences for disease transmission. For example, the arbovirus eastern equine Encephalitis (EEE), which is naturally found in birds, is transmitted in the United States by the mosquito Culiseta melanura. During spring and early summer, these mosquitoes feed almost exclusively on passerine birds, transmitting the virus among them. Later in the season, as mosquito numbers increase, bird defensive behavior increases and mosquitoes are more willing to feed on other vertebrate hosts. This is when EEE is transmitted to other vertebrates including horses and humans.

See Also the Following Articles

Medical Entomology • Mosquitoes • Phthiraptera • Siphonaptera • Tsetse Fly • Veterinary Entomology

Further Reading

Beaty, B., and Marquardt, W (eds.) (1996). "The Biology of Disease Vectors."

University of Colorado Press, Boulder. Braks, M. A. H., Anderson, R. A., and Knols, B. G. J. (1999). Infochemicals in mosquito host selection: Human skin microflora and Plasmodium parasites. Parasitol. Today 15, 409-413. Charlab, R., Valenzuela, J. G., Rowton, E. D., and Ribeiro, J. M. C. (1999). Toward an understanding of the biochemical and pharmacological complexity of the saliva of a hematophagous sand fly Lutzomyia longipalpis. Proc. Nat. Acad. Sci. U.S.A. 96, 15155-15160. Clements, A. (1999). "The Biology of Mosquitoes." CABI Int., Oxon. Dye, C. (1992). The analysis of parasite transmission by bloodsucking insects. Annu. Rev. Entomol. 37, 1-19. Hurd, H., Hogg, J. C., and Renshaw, M. (1995). Interactions between bloodfeeding, fecundity and infection in mosquitos. Parasitol. Today 11, 411-416.

Lane, R., and Crosskey, R. (eds.) (1993) "Medical Insects and Arachnids."

Chapman & Hall, London. Lehane, M. J. (1991). "Biology of Blood-Sucking Insects." Chapman & Hall, London.

Sutcliffe, J. F. (1986). Black fly host location: A review. Can. J. Zool. 64, 1041-1053.

Titus, R. G., and Ribeiro, J. M. C. (1990). The role of vector saliva in transmission of arthropod-borne disease. Parasitol. Today 6, 157-160. Vale, G. A., Hall, D. R., and Gough, A. J. E. (1988). The olfactory responses of tsetse flies, Glossina spp. (Diptera: Glossinidae), to phenols and urine in the field. Bull. Entomol. Res. 78, 293-300. Waage, J. K. (1979). The evolution of insect/vertebrate associations. Biol. J. Linn. Soc. 12, 187-224.

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