In Japan, two newly identified species can be found: Aphanerostethus magnus (known as Oo-daruma-kuchikakushi-zoumushi) and Aphanerostethus japonicus (referred to as Nippon-daruma-kuchikakushi-zoumushi). Notably, Aphanerostethus japonicus is also located in Yanbaru National Park, Okinawa. This study marks the first time x-ray microtomography has been utilized to eliminate scales that hinder visibility and examine the morphological differences for classification purposes.
Jake Lewis, an entomologist working in the Environmental Science and Informatics Section at the Okinawa Institute of Science and Technology (OIST), has a deep interest in weevils, a broad category of beetles that features numerous species with nose-like mouthparts called rostrums. Weevils play significant roles in ecosystems, assisting with pollination and decomposition; however, some species are notorious for devastating agricultural fields and forests.
Through the application of x-ray microtomography—a 3D imaging method that uses x-rays to create detailed images of the internal structures—Lewis and his team successfully removed scales obscuring the surface of the weevils. Their analysis revealed considerable differences in the underlying cuticle across different species, making this an effective method for taxonomy and classification. By merging this technique with traditional light microscopy and DNA barcoding, the researchers discovered, characterized, and named 12 new weevil species from locations including Japan, Malaysia, Vietnam, and Taiwan. These newly identified species are relatively small, measuring between 1.5 to 3.0 mm long.
Two of these new species are found in Japan: Aphanerostethus magnus (Oo-daruma-kuchikakushi-zoumushi) and Aphanerostethus japonicus (Nippon-daruma-kuchikakushi-zoumushi). The latter can also be spotted in Yanbaru National Park, Okinawa. This groundbreaking study using x-ray microtomography to remove obstructive scales in order to analyze morphological differences has been documented in the journal Zookeys.
The researchers highlighted that x-ray microtomography effectively reveals major morphological variations between species, which are often difficult to detect with other techniques. As a result, this method is expected to become more popular in identifying new insect species, particularly those that are covered with scales or debris.
Lewis, who serves as the Insect Collection Manager at OIST and is the paper’s principal author, studied specimens from various collections around the world, including Canada, Germany, Japan, Malaysia, Taiwan, and the Netherlands. One of the primary objectives was to explore the role of x-ray microtomography in weevil taxonomy. Historically, the genus Aphanerostethus has seen limited research, yet numerous unidentified species were discovered within museum collections globally, including the two newly recognized species from Japan.
Using Multiple Techniques to Discover New Species
The research team employed traditional methods such as light microscopy and dissections to note distinctions among species, including the scales on the elytra (the protective wing covers), the spines on their legs, and the shapes of the rostral canal (which houses the rostrum). They also conducted DNA barcoding to analyze the genetic material of the species, creating a phylogenetic tree for eight of the species examined. Some species proved challenging to differentiate solely based on morphology, yet gene sequencing provided a clear distinction, bolstering evidence for the identification of new species.
While the techniques mentioned above are standard in taxonomy, the implementation of x-ray microtomography by the researchers was innovative, allowing a detailed examination of not only the concealed cuticle but also the hindwings. Species within the Aphanerostethus genus have evolved to lack the capability of flight, resulting in a gradual reduction of their hindwings, with varying degrees of loss among species. Typically, accessing the hindwings would necessitate dissection, but x-ray microtomography facilitates non-destructive analysis of internal anatomy. This is particularly valuable when studying rare or valuable specimens that should not be dissected or altered.
Observing partially reduced wings in certain species provides intriguing insights into ongoing evolutionary processes: “Some species have nearly completely lost their hindwings, while others possess non-functional half-wings, complete with remnants of vein patterns. The varying stages of hindwing reduction are not only relevant for taxonomy and systematics but also reveal that different species within the same group may be at varied evolutionary stages concerning a historically vital organ,” explained Lewis.
Supporting Japan’s Natural Heritage
Identifying new weevil species poses particular challenges, primarily due to two reasons. First, weevils exhibit remarkable diversity, making thorough cataloging a time-consuming and arduous process. Second, many weevil species are very specific regarding their host plants, may reside in unique microhabitats, and could be active only briefly as adults. As an illustration, specific species may solely feed on one type of tree and only occupy select areas of that tree, such as the upper canopy. Additionally, some weevil species are nocturnal, making daylight observations rare.
This high level of specialization and variation in their natural history suggests that without thorough research conducted by day and night, across different seasons and focusing on various plant parts, certain species may be overlooked.
Dr. Dan Warren, a research fellow at the Gulbali Institute for Applied Ecology and former leader of the Environmental Science and Informatics Section, underscored the necessity of investing in specimen collections: “These collections are vital for discovering new species and monitoring changes in biodiversity brought about by human actions and natural cycles. They serve as essential tools for scientific inquiry and conservation biology,” he remarked. “Without adequate support for these collections and their custodians, we risk losing invaluable information about species and ecosystems, perhaps even before we have the chance to discover them.”
“The new weevil species contribute to Japan’s natural heritage, and while their ecological roles remain poorly understood, identifying and naming them is the essential first step toward comprehending their biology,” Lewis stated. Protected regions such as Yanbaru National Park, which houses the newly found A. japonicus, play a critical role in preserving the island’s rich and unique biodiversity.
