Regurgitation And Defecation Of Allelochemicals

Enteric defense may be widespread in insects as a means of using the proven repellencies of a variety of plant natural products. In a sense, the intestine is functioning as a defensive organ once repellent plant products have been ingested, and it is likely that the presence of pharmacologically active plant compounds in the intestine renders the insect distasteful or emetic. Therefore, transfer of gut contents to the outside by either regurgitation or defecation could actually constitute the externalization of the internal enteric defenses.

When tactilely stimulated, acridid grasshoppers readily regurgitate, and this discharge, fortified with plant natural products, is very repellent to ants. Similarly, larvae of the moth Eloria noyesi regurgitate when molested. The enteric discharge, which contains cocaine extracted from the larval food plant, is very repellent to ants.

Defecation can also serve to externalize deterrent plant natural products. The large milkweed bug defecates readily when subject to traumatic stimuli, the discharge being fortified with emetic and distasteful cardenolides (steroids) derived from the milkweed host plants. The anal discharge, containing concentrated cardenolides, is very repellent to ants.

See Also the Following Articles

Aposematic Coloration • Autohemorrhage • Defensive Behavior • Monarchs • Venom

Further Reading

Blum, M. S. (1981). "Chemical Defenses of Arthropods." Academic Press,

New York.

Blum, M. S. (1996). Semiochemical parsimony in the Arthropoda. Annu.

Rev. Entomol. 41, 353-374. Dettner, K. (1987). Chemosystematics and evolution of beetle chemical defenses. Annu. Rev. Entomol. 32, 17-48. Duffey, S. S. (1977). Arthropod allomones: Chemical effronteries and antagonists. Proc. XV Int. Cong. Entomol. Washington, DC, pp. 323-394.

Duffey, S. S. (1980). Sequestration of plant natural products by insects.

Annu. Rev. Entomol. 25, 447-477. Edwards, J. S. (1961). The action and composition of the saliva of an assassin bug Platymeris rhadamanthus Gaerst. (Hemiptera: Reduviidae). J. Expt. Biol. 38, 61-77. Eisner, T. (1970). Chemical defense against predation in arthropods. In "Chemical Ecology" (E. Sondheimer and J. B. Simeone, eds.), pp. 157-217. Academic Press, New York. Hartmann, T. (1995). Pyrrolizidine alkaloids between plants and insects: A

new chapter of an old story. Chemoecology 5, 139-146. Kellner, R. L. L. (1999). What is the basis of pederin polymorphism in Paederus riparius rove beetles? The endosymbiotic hypothesis. Entomol.

Exp. Appl. 93, 41-49. Pasteels, J. M., and Gregoire, J.-C. (1983). The chemical ecology of defense in arthropods. Annu. Rev. Entomol. 28, 263-289.

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