The Life‐Styles of Tropical Milkweed Bugs, Oncopeltus (Hemiptera: Lygaeidae) Utilizing the Same Hosts

Abstract

Oncopeltus cingulifer and Oncopeltus unifasciatellus occur on the same milk—weed species in the Cauca Valley of Colombia. Adults utilize the major host, Asclepias curassavica in the same way except that O. unifasciatellus feeds somewhat more on seeds. Nymphs of O. unifasciatellus require milkweed seeds to develop whereas O. cingulifer can mature slowly while feeding only on vegetative tissues of milkweeds. Parasitism, predation, and cannibalism are responsible for heavy losses of eggs in both species. Cannibalism of unhatched eggs by their newly—hatched siblings has a complex adaptive basis involving the utilization of individuals that are otherwise doomed and the proportion of eggs parasitized in a clutch by scelionid wasps. The continuous growing season in the Cauca Valley, coupled with the asynchronous occurrence of catastrophic setbacks in different milkweed stands, results in a shifting distribution of seed abundance. The adaptive syndromes exhibited by Oncopeltus appear to be organize around their dependence on this patchy resource. Thus O. unifasciatellus, which requires seed for reproduction, is less sedentary and more phenotypically variable than O. cingulifer. It seems unlikely that two such species could coexist in a seasonal environment where seed production is synchronized over an entire region.