Visitation of a specialist pollen feeder Althaeus hibisci Olivier (Coleoptera: Bruchidae) to flowers of Hibiscus moscheutos L. (Malvaceae)1

SHIMAMURA, R., N. KACHI (Department of Biological Sciences, Graduate School of Sciences, Tokyo Metropolitan University, Hachioji 192-0397, Japan), H. KUDOH (Department of Biology, Faculty of Science, Kobe University, Kobe 657-8501, Japan), AND D. F. WHIGHAM (Smithsonian Environmental Research Center, Edgewater, MD 21037). Visitation of a specialist pollen feeder Althaeus hibisci Olivier (Coleoptera: Bruchidae) to flowers of Hibiscus moscheutos L. (Malvaceae). J. Torrey Bot. Soc. 132: 197–203. 2005.—We investigated visitation of a bruchid seed beetle, Althaeus hibisci Olivier, to flowers of Hibiscus moscheutos L. (Malvaceae) under natural conditions. We examined movement of the beetle among flowers that were in different developmental stages, the correlation between corolla size and pollen production, and the correlation between beetle density and corolla size. Beetles moved diurnally from wilted Hibiscus moscheutos flowers that had opened on the previous day to newly open flowers. Beetles did not move to unopened flowers as long as petals were covered by sepals. The results demonstrate that the beetles use corollas as a cue to locate flowers. Hibiscus moscheutos flowers produced pollen in proportion to corolla size; therefore, beetles visiting larger flowers had a high probability of finding larger amounts of pollen. We detected positive correlations between beetle density and petal area when beetles were abundant. Although the correlation coefficients were small (r 5 0.24–0.32), they were statistically significant or marginally significant. On the other hand, the correlations were not significant when the density of beetles was low suggesting that the preference for larger flowers is not always detectable and its strength varies with beetle density under natural conditions.