Megachile timberlakei Cockerell (Hymenoptera: Megachilidae): Yet another adventive bee species to the Gala´pagos Archipelago Claus Rasmussen (corresponding author), Department of Bioscience, Aarhus University, Ny Munkegade 114, Bldg. 1540, DK-8000 Aarhus C, Denmark, [email protected]; Ana L. Carrı´on, Charles Darwin Foundation, Puerto Ayora, THE PAN-PACIFIC ENTOMOLOGIST 88(1):98–102, (2012) Scientific Note Megachile timberlakei Cockerell (Hymenoptera: Megachilidae): Yet another adventive bee species to the Gala´pagos Archipelago The Gala´pagos Archipelago is one of the most fascinating settings for a spectacular evolutionary scene, initially enchanting Charles Darwin during his travel with the HMS Beagle in 1835 and later inspiring his theory of evolution by natural selection (Darwin 1859). The insect fauna is limited as expected on a volcanic archipelago separated by a large body of water with more than 1000 km to the nearest mainland, Ecuador. The biological paucity of diversity and abundance was noticed initially by Darwin: ‘‘I took great pains in collecting the insects, but, excepting Tierra del Fuego, I never saw in this respect so poor a country’’ (Darwin 1846:164). Of the insects, the bee fauna from Gala´pagos is well known, with a single endemic carpenter bee abundant on all major islands of the archipelago (Xylocopa darwini Cockerell 1926 (Apidae)). Earlier insect studies have reported only this species and subjected it to several biological studies (e.g., Williams 1926, Linsley 1965, Linsley et al. 1966, Hurd 1978). Considering the apparently well-known bee fauna, it was surprising that a second bee was recently reported (Causton et al. 2006, Gonzalez et al. 2010), the wool carder bee Anthidium vigintiduopunctatum Friese 1904 (Megachilidae) from the island of Floreana. This species was previously known only from Peru and mainland Ecuador (Gonzalez et al. 2010). Floreana was one of the earlier islands to be inhabited and A. vigintiduopunctatum may have inadvertently been introduced during the long history of frequent contact and exchange with mainland South America. We here report the leaf-cutter bee Megachile (Eutricharaea) timberlakei Cockerell 1920 (Megachilidae) as a third bee species in the Gala´pagos. The species is currently known from the Hawaiian Islands and was collected during floral inventories on San Cristo´bal. We provide floral records as well as a diagnosis and comparative comments that will assist bee researchers to easily recognize this species from other native and adventive Megachile Latreille to the Americas. We also discuss the possible routes to the Gala´pagos. Several individuals of M. timberlakei were observed and collected during floral inventories on 2–4 March 2010, in the dry zone of the inhabited island of San Cristo´bal, along Sendero Tijeretas. Either or both sexes of M. timberlakei were observed (by ALC, RCU and SC) visiting the flowers of Alternanthera echinocephala (Amaranthaceae), Cordia lutea (Boraginaceae), Mentzelia aspera (Loasaceae), Bastardia viscosa (Malvaceae), and Waltheria ovata (Sterculiaceae). These plants are all native to the Gala´pagos and mainland South America (Lawesson et al. 1987). In Hawaii, nests of M. timberlakei are found in crevices and consist of long series of cells, attached end to end by overlapping leaf-segments. Each cell is 8–9 mm long and 7 mm in diameter (Timberlake 1921). More detailed nest studies from Hawaii of M. timberlakei have been conducted using trap nests (Kim 1992), a technique that could be applied on the Gala´pagos to survey whether the species is also present on other islands, in addition to providing information about the flight period and pollen range used in cell provisions. 2012 SCIENTIFIC NOTE 99 The little-known Megachile timberlakei is hitherto known from the far away Hawaiian Islands where it is common on the islands of Hawaii, Kaui, Lanai, Maui, Midway and Oahu (Snelling 2003), but ever since the description it has been speculated that the species is actually not native to Hawaii (Cockerell 1920, Timberlake 1921, Snelling 2003). The male and female specimens here reported from the Gala´pagos are identical to specimens of M. timberlakei from Hawaii, including the male genitalia. The only difference noticed is the slightly larger body size when compared to those from Hawaii. Among adventive species of Eutricharaea Thomson in the New World, M. timberlakei is most similar to M. rotundata in the following characters: female metasomal sterna with complete and conspicuous white apical hair fasciae beneath scopa; last female sternum with scopal hairs dark brown, contrasting with whitish scopal hairs on remaining sterna; male gena behind mandibular base barely projected, not forming a distinct tooth clearly seen in facial view; and male probasitarsus unmodified. It can be easily distinguished from that species by the narrow vertex in both sexes, which is about 1.2 to 1.5 times the diameter of the median ocellus in the female and male, respectively. In M. rotundata, it is at least twice as long as the median ocellar diameter. Additionally, in the male of M. timberlakei the profemur is widest near apex and distinctly yellow ventrally on its apical one-third, and the mesoscutum is distinctly covered with long, appressed, densely plumose hairs on its anterior and posterior margins in addition to erect, simple hairs. In M. rotundata the male profemur is widest about midlength, with its ventral margin not distinctly yellow apically, and the long, appressed, densely plumose hairs on the anterior and posterior margins of the mesoscutum are sparse to nearly absent. The subgenus Eutricharaea includes about 300 species distributed throughout the Palearctic, African, Oriental, and Australian areas, but is apparently not natural in the New World (Michener 2007, Ascher & Pickering 2012), although many species are found in the South Pacific region (Michener 1965). A few Eutricharaea species such as the alfalfa bee, Megachile rotundata (Fabricius 1793), are intensively used in crop pollination and have been introduced recently throughout the world, including North America, the Antilles, Argentina and Chile (Ruz 2002, Pitts-Singer & Cane 2011). To date, nine adventive Eutricharaea species have been recorded in the New World, including Hawaii (Table 1); some of them were described from specimens collected in the Caribbean (i.e., M. concinna from Dominican Republic, M. derelictula from Barbados, and M. multidends from Jamaica) and the Hawaiian islands (M. timberlakei) (e.g., Mitchell 1962, Snelling 2003, Moure et al. 2008). Megachilids are notable as the primary source of invasive bees, including multiple species of Anthidium Fabricius and Megachile (e.g., Cane 2004, Michener 2007), and it is therefore not surprising that the native range of those Eutricharaea recorded in the Americas or Hawaii is likely elsewhere. Megachile timberlakei, however, is still not known outside of Hawaii and now Gala´pagos. The actual native range of M. timberlakei thus also remains enigmatic as in those species described from the Americas (Table 1). A global taxonomic revision of the Eutricharaea is doubtless needed as well as molecular studies to determine the actual native range of those species in the Americas. The colonizing insect fauna of Gala´pagos has come almost entirely from the Americas (Kuschel 1963); the present record of a Hawaiian origin is therefore unexpected. Few other introduced taxa to Gala´pagos share a Pacific or Hawaiian 100 THE PAN-PACIFIC ENTOMOLOGIST Vol. 88(1) Table 1. Summary of known species of Megachile subgenus Eutricharaea adventive in the New World, including Hawaii. Approximate distribution ranges were taken from Moure et al. (2008) and Ascher & Pickering (2012), noting that both sources are not comprehensive compilation of specimen and literature records. ? 5 uncertain native range (see discussion). Species Native range Invasive range M. apicalis Spinola 1808 Palearctic North America M. chlorura Cockerell 1918 Southeast Asia Hawaii M. concinna Smith 1879a Africa? Palearctic, North America, Caribbean M. derelictula Cockerell 1937 Sub-Saharan Africa? Caribbean M. diligens Smith 1879b Southeast Asia? Hawaii M. fullawayi Cockerell 1914 Southeast Asia Hawaii M. multidens Fox 1891 South Africa? Caribbean M. rotundata (Fabricius 1793) Palearctic Oriental, Australia, New Zealand, North and South America M. timberlakei Cockerell 1920 Southeast Asia? Hawaii, Gala´pagos origin (Peck & Kukalova´-Peck 1990, Peck 2001), but Thinophilus hardyi Grootaert & Evenhuis (Dolichopodidae) from the Hawaiian Islands, with no close relatives in North or Central America, was also introduced to Gala´pagos (Bickel & Sinclair 1997). It remains a possibility that M. timberlakei was first accidently introduced to South America from Hawaii, where it remains unreported, and only subsequently was introduced to the Gala´pagos, as here reported. The depauperate bee fauna of the Gala´pagos makes it easy to detect in contrast to the highly diverse, abundant and yet poorly known South American mainland Megachile fauna. With a very limited native pollinator fauna (McMullen 1993), Gala´pagos may be particularly susceptible to the negative consequences of introduced pollinators, such as competition with native pollinators for floral resources, competition for nest sites, pollination of exotic weeds and disruption of pollination of native plants (Goulson 2003). All three bee species (one native and two apparently introduced) now known from the Gala´pagos are polylectic and very