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 academy 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 se beetle, Althaeas hibisci Olivier, to flowers of Hibiscus moscheutos L (Malvaceae) below natural conditions. We examined change 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 mov diurnally from wilted Hibiscus moscheutos flowers that had uncloseed on the previous day to newly make open flowers. Beetles did not propel to unopened flowers as lengthy as petals were covered by the agency of sepals. The results demonstrate that the beetles use corollas as a wink to locate flowers. Hibiscus moscheutos flowers produc pollen in proportion to corolla size; therefore, beetles visiting larger flowers had a high probability of finding larger amounts of pollen We descryed positive correlations between beetle density and petal area when beetles were abundant. Although the correlation coefficients were small (r = 024-032) they were statistically significant or marginally significant. upon the other hand, the correlations were not significant when the density of beetles was depressed suggesting that the preference for larger flowers is not always detectable and its might varies with beetle density below natural conditions.

Key words: Althaeus hibisci, bruchid beetle, floral attraction, flower size, foraging, freshwater wetland, Hibiscus moscheutos, Maryland, pollen production.

In many plant species, corolla size varies among and within individuals (Bell 1985 Galen 1999 Wolfe and Krstolic 1999) Theoretically, if corolla size correlates with the amounts of resources provided by dint of flowers, then insect visitors should pick out flowers based on corolla size to bring the costs of movement and maximize their rates of resource gain. Previous studies have shown that pollinators address to visit flowers with larger corollas (Bell 1985 Young and Stanton 1990 Stanton et al. 1991 Johnson et al. 1995)

Corolla size might also be important in determining the selection and behavior of small insect visitors (eg thrips, flies, small bees, and small beetles). Small insects are set to serve as pollinators in a certain quantity of systems (Momose et al. 1998a, b; Sakai et al. 1999) As pollen/ovule feeder small insects may considerably restore reproductive success of larger flowers (Brody 1992 Mutikainen and Delph 1996) Furthermore, small insects ofttimes use flowers as a site of mating and oviposition (Feller et al. 2003)

In this application of mind we investigated the responses of a bruchid se beetle, Althaeus hibisci Olivier (hereafter referr to as A. hibisci), to natural corolla size variation in Hibiscus moscheutos L (hereafter referr to as Hibiscus) flowers. Adults of A. hibisci visit Hibiscus flowers and forage for pollen (Spira 1989 Kudoh and Whigham 1998) Kudoh and Whigham (1998) reported that the density of A. hibisci upon H. moscheutos flowers decreased when petal size was artificially reduc to the smallest size class lay the foundation of in natural populations. Under natural conditions, H moscheutos exhibits continuous variation in corolla size. To understand the impact of A. hibisci upon seed production it is necessary to understand in what manner these beetles respond to the natural variation in a floral trait.

To evaluate the issues of corolla size on flower estimation by A. hibisci, we addressed the following questions: (1) Does A. hibisci arrive at Hibiscus flowers before or while they are open? (2) Is corolla size used as a hint in flower choice by A. hibiscil (3) Does corolla size correlate with the amount of pollen in Hibiscus flowers? (4) Does the density of A. hibisci in flowers correlate with corolla size?

Materials and meanss STUDY SYSTEM. Hibiscus moscheutos L (Malvaceae) is a herbaceous perennial native to freshwater and brackish marshes of eastern North America (Brown and Brown 1984) Plants have hardly any to many upright stems, 1-2 m tall. The flowering season stretch outs from late July to early September, and the flowers are relatively large (10-15 cm across), with white or pink petals that make open for a single day (Spira 1989) Flowers unclose at dawn and close by dint of night (Fig. 1). Time of anthesis may hang on temperature because anthesis is delayed upon rainy days and later in the flowering season (Ryouji Shimamura, personal observation). Flowers are pollinated mainly by means of an anthophorid bee, Ptilothrix bombiformis Cresson and by the agency of a bumblebee, Bombus pennsylvanicus DeGeer (Spira 1989) The flowers are self-compatible, on the other hand spatial separation of the stigmas and the anthers impedes automatic selfpollination (Spira 1989).