Flowering mechanisms, pollination strategies and floral scent analyses of syntopically co‐flowering Homalomena spp. (Araceae) on Borneo

Abstract

In this study, the flowering mechanisms and pollination strategies of seven species of the highly diverse genus Homalomena (Araceae) were investigated in native populations of West Sarawak, Borneo. The floral scent compositions were also recorded for six of these species. The selected taxa belong to three out of four complexes of the section Cyrtocladon (Hanneae, Giamensis and Borneensis). The species belonging to the Hanneae complex exhibited longer anthesis (53-62 h) than those of the Giamensis and Borneensis complexes (ca. 30 h). Species belonging to the Hanneae complex underwent two floral scent emission events in consecutive days, during the pistillate and staminate phases of anthesis. In species belonging to the Giamensis and Borneensis complexes, floral scent emission was only evident to the human nose during the pistillate phase. A total of 33 volatile organic compounds (VOCs) were detected in floral scent analyses of species belonging to the Hanneae complex, whereas 26 VOCs were found in samples of those belonging to the Giamensis complex. The floral scent blends contained uncommon compounds in high concentration, which could ensure pollinator discrimination. Our observations indicate that scarab beetles (Parastasia gestroi and P. nigripennis; Scarabaeidae, Rutelinae) are the pollinators of the investigated species of Homalomena, with Chaloenus schawalleri (Chrysomelidae, Galeuricinae) acting as a secondary pollinator. The pollinators utilise the inflorescence for food, mating opportunities and safe mating arena as rewards. Flower-breeding flies (Colocasiomyia nigricauda and C. aff. heterodonta; Diptera, Drosophilidae) and terrestrial hydrophilid beetles (Cycreon sp.; Coleoptera, Hydrophilidae) were also frequently recovered from inflorescences belonging to all studied species (except H. velutipedunculata), but they probably do not act as efficient pollinators. Future studies should investigate the post-mating isolating barriers among syntopically co-flowering Homalomena sharing the same visiting insects.

Novel Floral Scent Compounds from Night-Blooming Araceae Pollinated by Cyclocephaline Scarabs (Melolonthidae, Cyclocephalini)

“…Its presence in high concentrations as a floral scent is most remarkable in brood pollination systems involving Yucca spp. (Agavaceae) and yucca moths (Lepidoptera, Prodoxidae) (Gäbler et al 1991 ; Svensson et al 2005 ), but it has also been documented as a major constituent in scarab beetle-pollinated aroids of the genus Homalomena in Borneo (Hoe et al 2016 ). Interestingly, ( E )-cyclanthone and other unique derivatives of DMNT have been described from the floral scent of Cyclanthus bipartitus Poit.…”

Synopsis of the cyclocephaline scarab beetles (Coleoptera, Scarabaeidae, Dynastinae)

“…In contrast, the labral morphology of Peltonotus species matches that found in Asian parastasiine and fruhstoferiine (Rutelinae) scarabs (Arrow 1908, 1910). The floral feeding behavior of Peltonotus species on Araceae is also shared between cyclocephalines and Asian parastasiines, adding a further layer of intrigue to unresolved evolutionary relationships between the groups at the subfamilial- and tribal-level (e.g., see Moore and Jameson 2013, Kumano-Nomura and Yamaoka 2006, Kumano-Nomura and Yamaoka 2009, Tung et al 2010, Hoe et al 2011, 2016). …”

2‐Alkyl‐3‐methoxypyrazines are potent attractants of florivorous scarabs (Melolonthidae, Cyclocephalini) associated with economically exploitable Neotropical palms (Arecaceae)

“…For instance, p ‐methylanisole (a methoxylated benzenoid) and ( E )‐4,8‐dimethyl‐1,3,7‐nonatriene (a homoterpene), also found in high relative amounts in analyzed samples of all four studied species (Table S2, Fig. S1), had both been previously described as main floral scent constituents of angiosperms associated with anthophilous scarabs …”

“…S1), had both been previously described as main floral scent constituents of angiosperms associated with anthophilous scarabs. 11,39,40 Alluding to successful cases of insect pest control associated with palm crops, such as those of palm weevils of the genus Rhynchophorus (Curculionidae, Rhynchophorini), 41,42 better understanding of the chemical ecology of florivorous cyclocephaline scarabs is central for future integrated management plans. In a scenario in which tropical South American economies are invested in finding complementary alternatives to the cultivation of African oil palm (Elaeis guineensis) through the domestication of native high oil-yielding palms, 43,44 the identification of MPs as potent kairomones could prove to be an important asset.…”