A wonderful world of weevils : A new species of Karekizo from the Alishan Mountains, Taiwan

A wonderful world of weevils : A new species of Karekizo from the Alishan Mountains, Taiwan

Weevils (Coleoptera: Curculionidae) represent a mega-diverse group of beetles which are characterized by the possession of modified mouthparts which resemble the trunk of an elephant (in fact, the Japanese name for weevil is zou-mushi, which translates to elephant bug). This trunk-like set of modified mouthparts are collectively referred to as the rostrum. The rostrum is used by many weevils to bore into their hosts and substrate, and its evolution likely played a major role in the diversification of weevils during the radiation of Angiosperms. With over 63,000 described species and many more awaiting discovery, weevils not only play a major role in ecosystems worldwide but are remarkably diverse in form and behavior (Figure 1). Recently, phylogenomic studies have begun to reveal the phylogenetic relationships between the families and subfamilies of weevils; however, the phylogenetic relationships of many genera are still unknown and, with so many species still awaiting discovery, our understanding of weevil is far from complete.

Although some weevil species are generalists and use a variety of species as host plants, many species use only one host plant species. It is often these specialist species with narrow host preferences which are most sensitive to anthropogenic disturbance (e.g., deforestation, harvesting) and climate warming, as they do not have the option of shifting to alternative host plants when their host plant becomes scarce. This has been and will continue to be a major problem for biodiversity conservation, and unfortunately some specialist weevil species have already gone extinct due to human-related activities. In North America, the Greater Chestnut Weevil (Curculio caryatrypes (Boheman, 1843)) fed only on American Chestnut (Castanea dentata), but when the Asian chestnut blight (Cryphonectria parasitica) was introduced to New York City it decimated American Chestnut trees across the continent which lacked immunity to the alien pathogen; the Great Chestnut Weevil has not been observed since 1987 and is now thought to be extinct (See the following post for more information: https://nature.ca/en/co-extinction-and-the-case-of-american-chestnut-and-the-greater-chestnut-weevil-curculio-caryatrypes/). In order to protect species, we must first know of their existence and natural history. For this reason, species discovery is not only important to a complete understanding of weevil evolution, but also for conservation.

Jake Lewis of the Environmental Science and Informatics Section manages OIST’s insect collection and specializes in weevil taxonomy. He has been working on identifying the weevils in the OIST insect collection, and has also visited Kyushu University a few times to view their rich reference collection and type material. During Jake’s work at Kyushu University, he came across an undescribed weevil species in the genus Karekizo from Taiwan, and recently described it in Zootaxa. The newly described species, named Karekizo depressus (Figure 2), differs from the only other member of the genus K. impressicollis in the dorsal profile of the femora (the first major segment of the leg in weevils). In K. impressicollis this profile is straight (Figure 3a), in K. depressus it is distinctly depressed (Figure 3b), hence the specific name depressus. The new species also differs in color, size, and in the shape of the male genitalia (Figure 3c, d). The shape of the male (and to a lesser extent female) genitalia is often very important in beetle taxonomy as it allows for species level identification and contains phylogenetically important characters. The genus Karekizo was described based on a single species (K. impressicollis Morimoto, 1962) from mainland Japan, and is closely related to the much more diverse genera Trachodes and Acicnemis. Although most scientific names are derived from Latin, the genus name Karekizo is derived from the Japanese words Kareki (meaning dead / decaying tree) and zo (part of the Japanese word for weevil). Members of the genus are associated with mountainous regions, and possibly for the same reason, are not commonly collected.

Figure 1. A) Xenysmoderes consularis (Pascoe, 1869) can be found commonly in Okinawa during the spring on Alpinia sp. flowers. This species uses its modified hind legs to jump around when disturbed, an ability which has evolved independently a number of times in weevils. B) Karekizo impressicollis Morimoto, 1962 is found in mainland Japan and on Jeju Island (South Korea) and is associated with mountainous regions. C) Listronotus delumbis (Gyllenhal, 1834) occurs in wetlands across North America and is known for its abilities as a strong swimmer. D) Cosmobaris scolopacea Germar, 1819 is found across Europe and Asia, and also occurs uncommonly on Okinawa Island. E) Scepticus griseus Roelofs, 1873 is commonly found along Okinawa Island’s sandy coastlines on a variety of plants and flowers. F) Demimaea fascicularis (Roelofs, 1879) is a beautiful black-and-white east Asian species which occurs on Ficus erecta and other Moraceae.

Figure 2. Karekizo depressus Lewis, 2023.

Figure 3. A) Karekizo impressicollis femur with straight dorsal edge (micro-ct). B) Karekizo depressus femur with depression along dorsal edge at midpoint. C) K. depressus aedeagus (penis). D) K. impressicollis aedeagus.