The Ecology and Behavior of a Subsocial Pentatomid Bug and Two Scelionid Wasps: Strategy and Counterstrategy in a Host and Its Parasites

Eberhard, William G. The Ecology and Behavior of a Subsocial Pentatomid Bug and Two Scelionid Wasps: Strategy and Counterstrategy in a Host and Its Parasites. Smithsonian Contributions to Zoology, number 205, 39 pages, 13 figures, 24 tables, 1975.—The tropical bug Antiteuchus tripterus and two parasites of its eggs, Trissolcus bodkini and Phanuropsis semiflaviventris, were studied in urban Cali, Colombia. Female bugs guard both their eggs and first instar nymphs. Behavioral observations, combined with analyses of the patterns of parasitism within egg masses of a given form, showed that the details of the bug's defensive behavior and the wasps' attacks strongly influence the survival rates of eggs in different positions in an egg mass. By removing guarding female bugs from their eggs, it was shown that the net effect of their defense against generalized egg predators is to greatly improve egg survival but that, paradoxically, the net effect against the parasitic wasps is to decrease survival. Although the bugs repel wasps that have found egg masses, the bug's presence over the mass betrays the location of the eggs to hunting wasps. A hypothetical evolutionary history suggests that as the bugs improved their protection of eggs, they produced thinner egg shells, and that they are now trapped into continuing their defense in spite of subsequent advances by the wasps in their hunting behavior. Experimental removal of bugs guarding first instar nymphs and calculations of the cost of guarding in terms of egg production showed that the net effect of this guarding behavior is positive. Female P. semiflaviventris tend to stay and hunt in the tree where they emerge, while T. bodkini females tend to disperse. Parasitism rates by P. semiflaviventris are strongly influenced by the species of tree where the bug eggs are laid, and both species are influenced by the site of the egg mass (leaf, branch, sucker), but in different ways. Both species also wait near bugs about to oviposit and attack eggs as they are laid, apparently recognizing gravid bugs visually. Parasitism rates of eggs on naturally and experimentally isolated leaves showed that search behavior is accomplished in flight. Natural selection with respect to oviposition site varies greatly with tree species and the site on a given tree. The balance of selection was evidently different where the bugs evolved than in present-day Cali, where they commonly act against their own best interests. Both wasp species agree in general with the behavior pattern for Scelionidae, but differ in several characteristics associated with oviposition. P. semiflaviventris is consistently farther from the family norm than is T. bodkini. The two species of wasp compete at two stages in their life cycle, with neither species consistently dominating. The males fight and exclude each other from egg masses where females will emerge, and multiple ovipositions into single bug eggs produce only single wasps. Both types of competition occur commonly in urban Cali. Many other aspects of the natural history and ecology of the bugs and wasps are presented. OFFICIAL PUBLICATION DATE is handstampcd in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 5381. SERIES COVER DESIGN: The coral Montastrea cavernosa (Linnaeus). Library of Congress Cataloging in Publication Data. Eberhard, William G. The ecology and behavior of a subsocial pentatomid bug and two scelionid wasps. (Smithsonian contributions to zoology ; no. 250) Supt. of Doc. no.: SI 1.27:205 1. Antiteuchus tripterus. 2. Trissolcus bodkini. 3. Phanuropsis semiflaviventris. 4. Hostparasite relationships. 5. Insects—Behavior. I. Title. II. Series: Smithsonian Institution. Smithsonian contributions to zoology ; no. 205. QL1.S54 no. 205 no. 205 [QL523.P5] 591'.08s [595.7'54] 75-619087