Synopsis of the Genera of Hawaiian Cossoninae with Notes on Their Origin and Distribution (Coleoptera, Curculionidae)

OCCASIONAL PAPERS OF BERNICE P. BISHOP MUSEUM HONOLULU, HAWAII Volume XV May 20,1940 Number 25 ..._-_._ .. -._--------- Synopsis of the Genera of Hawaiian Cossoninae with Notes on Their Origin and Distribution (Coleoptera, Curculionidae) By ELWOOD C. ZIMMERMAN ENTOMOLOGIST, BERNICE P. BISHOP MUSEUM INTRODUCTION The principal purposes of this paper are to present a key for the identification of the genera of Cossoninae found in Hawaii and briefly to discuss each genus in the light of its endemicity, deriva tion, and distribution. The supraspecific classification of the Cossoninae is chaotic. A complete revision of the subfamily is greatly needed. The genera must be evaluated and redefined; many need to be united and numerous new genera must be erected. Such a revision can be done only hy an experienced monographer working probably at the British Museum, where, I have been told, most of the genera and more than 80 percent of the species are represented. I hope that such a revision soon will come from Sir Guy Marshall. The Cossoninae reach their peak of development in the Indo Pacific regions; but it is in those vitally important areas that we know, comparatively speaking, the least about the group. The in sular regions of the world support many times the number of species on the continents, and the subfamily has come to be looked upon as one of the most successful colonizers of islands. In Polynesia, especially, the Cossoninae form one of the major components of the terrestrial faunas. In Hawaii there are only three subfamilies of Curculionidae which have developed endemic species in the islands: Otiorrhynchinae, 272 Bernice P. Bishop Museum-Occasional Papers XV, 25 Cryptorhynchinae, and Cossoninae. The Otiorrhynchinae are repre sented by one genus, Rhyncogonus, which is widely distributed in Polynesia east of Samoa; it contains 34 endemic Hawaiian species. The Cryptorhynchinae are represented by two genera: Acalles, which is world-wide, but composite, and which contains 22 endemic Hawaiian species, and Chaenosternum, which is endemic and contains one species. The Cossoninae are represented by 12 genera, which have 106 endemic species among them; and 7 of these 12 genera are con sidered endemic to Hawaii. These relationships can be graphically expressed in percentages as follows: 80 percent of the Hawaiian curculionid genera which include endemic species are Cossoninae, 13.3 percent are Cryptorhynchinae, and 6.6 percent are Otiorrhynchinae. There are 163 species of Hawaiian Curculionidae considered endemic products, of which 65 percent are Cossoninae, 20 percent Otior rhynchinae, and 14 percent Cryptorhynchinae. Samoa has 12 sub families of Curculionidae that have developed endemic species in those islands. If for the sake of comparison, we exclude all the others and consider only the genera of Samoan Otiorrhynchinae, Crypto rhynchinae, and Cossoninae that contain endemic species, we have the following results: 60 percent are Cossoninae, 33 percent Crypto rhynchinae, and 6 percent Otiorrhynchinae. The endemic Hawaiian Cossoninae average 8.1 species to the genus; the endemic Samoan species average only 1.3 species to the genus; this average is weighted on the Hawaiian side by the extensive developments of the genera Dryopthorus and Oodemas, particularly. This differential may be changed by more careful collecting in Samoa, but the ratio will not come near to that of the Hawaiian fauna. Much more speciation has gone on in the Hawaiian genera than in the Samoan genera. This can be interpreted as meaning that greater age and, most significantly I believe, greater, more constant, and more prolonged isolation must be attributed to the Hawaiian cossonine fauna. Any discussion of the origin and development of the endemic components of the Hawaiian fauna must, I believe, take into con sideration that long chain of remnants of islands lying to leeward of the major Hawaiian islands from Kauai to Midway and Kure (Ocean) Islands. Apparently the outlying islands affected some groups, but not others. Biologists believe that parts of the Hawaiian Zinuner'l1lan-Hawai-ian Cossoninae 273 fauna indicate greater ages for the islands than those set forth by most geologists. However, without diverging greatly from the opin ions of some geologists one might consider some of the outlying Hawaiian islands (Nihoa to Kure) to have been more extensive and higher during the Tertiary. Perhaps some of them supported a con siderable flora and fauna, even as far back as middle Tertiary times; and perhaps some of the more aherrant and anomalous genera had their beginnings in the leeward islands. Of all the oceanic islands, the Hawaiian Archipelago seems to me to present the most aberrant and anomalous insect fauna, and the most difficult of interpretation. Many of its genera are peculiar isolates whose relationships are most cryptic and whose allies are masked or have evidently heen lost among the dregs of the evolution of the Pacific faunas. QKAUAI lq:nHAU I OAHU ~ I MOLOKAl~ I LANAI I ):SMAUI KAHOOLAWE ~f- r;;> '5 ., ", ... ,n FIGURE 1. The distribution of endemic species among the main islands (map, fig. 1) presents some interesting and pertinent facts. It is generally agreed by geologists, I understand, that the islands are successively younger from Kallai on the north to Hawaii with its active volcanoes on the south, a thesis substantiated by biologists. 274 Bernice P. Bishop Museum-Occasional Papers XV, 25 The number of endemic species per island is not proportionate to the size of the island. If we tabulate the number of species of Cos soninae with the islands arranged roughly according to age, the re sults are as follows: TABU~ 1 N UMBER of GENERA N UMBER of ENDEMIC' ISLAND AREA IN CONTAINING ENDEMIC SpECIES AND SQUARE MII.ES SpECIEs SUBSPECIES ---_.. _--_.. --_.. _---_._- ..... Kauai 555 6 29 Oahu 604 5 22 Maui 728 3 15 Molokai 260 2 3 Lanai 141 1 2 Hawaii 4,030 2 6 'By endemic species, I mean here those indigenous species which are confined to one island only. The totals for the islands of Molokai and Lanai are less accurate than for the others, because they are small islands with limited areas of undisturbed native forest, and they have not been adequately explored. Lanai and Molokai are close to Maui and are considered by Stearns to have been connected, above water, with Maui. A number of species of Hawaiian insects inhabit all three of these islands, or one or the other and Maui. Some Maui species have "varieties" on Molokai or Lanai. Kauai is the richest island in species and is inhabited by repre sentatives of all of the endemic Hawaiian cossonine genera, and one endemic genus' (Dyssoma) is confined to Kauai. It is probable that most of the endemic cossonine genera underwent considerable evolu tion and speciation on Kauai before their representatives were dis tributed southeastward among the other islands. The orderly picture of distribution presented by the Cossoninae is not true of all groups of beetles, however. In some families, certain genera evidently arrived in the archipelago after some of the younger islands were formed, speciating greatly on certain islands but not reaching others. The Carabidae is such a group. In the Nomiini (Carabidae), for example, at least 78 species have been described, Zimlllennun-HU'lmiiun Cossoninue 275 but no specimen has eve!;" been found on Kauai. These species are distributed as follows: Oahu 3, l\1aui 41, Molokai 18, Lanai 2, Hawaii 14. HO\\iever, Kauai is the headquarters for the Bembidiini (Cara hidae), and the development and distribution of that group parallels that of the Cossoninae. In "Fauna Hawaiiensis", there were recorded seven genera containing endemic Bembidiini on Kauai, but only three genera are represented among all of the other islands. Kauai has 14, Oahu 5, Matti 5, Molokai 4, Lanai none, and Hawaii 1 endemic species. KI~Y TO TIlE GENERA OF I-L'\WAIlAN COSSONINAE I. Antennal funicle 4-segmented h.. .... h ... h_ .. 2 Antennal funicle 5- or 7-segrilented .. h h .. .. 3 2(1)_ Eyes distant from the prothorax, widely separated below..Dryopthorus. Lower ends of the eyes contiguous to the prothorax, only narrowly separated below __ .. .. .. __ .. _.. __ .... .._.. .._..... .. Stenommatus. 3(I)_ Antennal funicle 5-segmented .. 4 Antennal funicle 7-segmented .. .........._._ .. .. .._..... __ ...._....... __ ...... .. 8 4(3). Antennal scape reaching back to or distinctly past the hind margin of the eye __ .. .. .. .. h .. _h .. __ h_ .. __ .. .... 5 Antennal scape not reaching back beyond the middle of the eye, never reaching to the hind margin h .. _h ......_.. .. .. 6 5(4). Distance between the fore and mid coxae almost as long as the dis tance between the mid and hind coxae; scrobes passing rapidly downward and not at all directed toward the eyesm mDryotribus. Distance between the fore and mid coxae only about one half as long as the distance between the mid and hind coxae; scrobes evidently expanded against the eye and not narrow and rapidly passing down ward at a distance from the eyes .... part (s. str.) of Stenotrupis. 6(4). Body rather densely clothed above with long, fine, prostrate, conspicu ous, golden, hairlike setae; head not at all constricted behind the eyes ....m__ m_m ...... m_ ......_.. h .. mh m..h Orothreptes. Body with at most short, minute, or inconspicuous setae, never con spicuously and densely clothed with golden hair; head qmstricted behind the eyes at least on the sides .. m_mm_mmmm_m ..._m_mm m_ 7 7(6). Intercoxal process of the prosternum as broad or broader than a fore coxa; cephalic constriction at the hind margins of the eyes h _ ___ .. m__ __ _._. __ .. _.. m __ ._ .._mm m__ .m_. __ _m m_. Pentarthrum. Intercoxal process of the prosternum narrower than the breadth '6f a fore coxa; cephalic constriction distant from the eyes __ .

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