Sequestration of Defenses against Predators Drives Specialized Host Plant Associations in Preadapted Milkweed Bugs (Heteroptera: Lygaeinae)

AbstractHost plant specialization across herbivorous insects varies dramatically, but while the molecular mechanisms of host plant adaptations are increasingly known, we often lack a comprehensive understanding of the selective forces that favor specialization. The milkweed bugs (Heteroptera: Lygaeinae) are ancestrally associated with plants of the Apocynaceae from which they commonly sequester cardiac glycosides for defense, facilitated by resistant NaNa+/K+-ATPases and adaptations for transport, storage, and discharge of toxins. Here, we show that three Lygaeinae species independently colonized four novel nonapocynaceous hosts that convergently produce cardiac glycosides. A fourth species shifted to a new source of toxins by tolerating and sequestering alkaloids from meadow saffron (Colchicum autumnale, Colchicaceae). Across three milkweed bug species tested, feeding on seeds containing toxins did not improve growth or speed of development and even impaired growth and development in two species, but sequestration mediated protection of milkweed bugs against two natural predators: lacewing larvae and passerine birds. We conclude that physiological preadaptations and convergent phytochemistry facilitated novel specialized host associations. Since toxic seeds did not improve growth but either impaired growth or, at most, had neutral effects, selection by predators on sequestration of defenses, rather than the exploitation of additional profitable dietary resources, can lead to obligatory specialized host associations in otherwise generalist insects

Proceedings of the FORUM HERBULOT 2001 Neotropical Geometridae: Approaches to a Modern Concept of the Geometrid System on Genus and Tribe Level (8.3.-9.3.2001)

Volume: 24Start Page: 193End Page: 20

Rhodostrophia

<i>Rhodostrophia. vartianae</i>: Wiltshire, 1966 <p>(p. 134, figs. 42, 44)</p> <p> <b>Material examined.</b> Holotype 3 (examined), ‘Afghan[istan] centr. O v. | Bend-i-Amir, 3600m | 29.VII.1963 | Kasy & Vartian leg.’, ‘ <i>Rhodostrophia</i> | <i>vartianae</i> Wiltsh | Holotype 3’[abdomen missing, no preparation lable]. P a r a t y p e s (3 3examined): 1 3, same data, ‘Paratypoid <i>Rhodostrophia vartianae</i> Wiltshire 3’, ‘ Paratype | <i>Rhodostrophia vartianae</i> Wiltshire | det. H. R., 2009’, ‘prep. |1533/2011 | H. R.’; 2 3, same locality but different altitude and date as label: ‘ 3000m, 30.VII.1963 ’, ‘ Paratype | <i>Rhodostrophia vartianae</i> Wiltshire | det. H. R., 2009’; all in NHMW.</p> <p> <b>Redescription</b> (figs. 1–6). Female unknown. Wingspan: 3 34–36 mm. Antenna of male quadripectinate. Head (apex) white, frons slightly protruding about one-fourth of the eye diameter, light brown in colour. Palpi short, not reaching the clypeus. Thorax dark grey, abdomen light brown. Colour of wings brown-ochre. Post-median grey spot of forewing hardly visible in some specimens. The underside is slightly brighter than the upperside. Hump form projections of sternite A-8 well developed (fig. 15).</p> <p> <b>Male genitalia</b> (figs. 16–18). Valva flat, ventral part curved interiorly, dorsal part plicated. Uncus elongated, cleft at the tip. Juxta oval. Saccus short, rounded. Aedeagus long (1.5 mm) and arched, multiple small subapical granules present.</p> <p> <b>Biology and distribution</b> (Map 1). The larval stages and the biology are unknown. <i>R. vartianae</i> has been collected from high altitudes in central Afghanistan (Band-i Amir, 3000–3600m, Kasy & Vartian).</p> <p> <b>MAP 1.</b> Distribution of <i>Rhodostrophia lenis</i> and <i>R. vartianae</i>.</p> <p>We thank Sabine Gaal-Haszler (Wien) for sending type materials from NHMW, and Helen Alipanah (Tehran) for loan of material from HMIM. Wolfgang ten Hagen (Mömlingen, Germany) and Christian Wieser (Pischeldorf, Austria) provided us with material, data and photos. Jaan Viidalepp (Tartu), Dieter Stüning (Bonn), and Axel Hausmann (Munich) offered valuable comments on the manuscript, and Thomas Swinehart (Bonn) proofread the manuscript. The senior author thanks J. W. Wägele (ZFMK, Bonn) and DAAD (Deutscher Akademischer Austausch Dienst) for financial support, which is part of a doctoral dissertation project at the University of Bonn, Germany.</p>Published as part of <i>Sh, Hossein Rajaei & Trusch, Robert, 2011, Redescription of Rhodostrophia leni s Wiltshire 1966 and R. vartianae Wiltshire, 1966, with new distributional data (Lepidoptera, Geometridae, Sterrhinae), pp. 59-63 in Zootaxa 2935</i> on pages 60-63, DOI: <a href="http://zenodo.org/record/207740">10.5281/zenodo.207740</a&gt