Discovery of the diving beetle Laccornis oblongus (Stephens, 1835) in Bavaria, southern Germany (Coleoptera, Dytiscidae, Hydroporinae, Laccornini)

The diving beetle Laccornis oblongus (Stephens, 1835) is recorded for the first time from Bavaria, southern Germany, which marks the most south-westerly record of the species known to date. Three specimens were collected in the Murnauer Moos nature reserve in Upper Bavaria. We summarize what is known about the species habitat in Germany and provide photographs of the sampling site and habitus, median lobe of aedeagus, and paramere of the species. We provide a checklist of the 20 other diving beetle species we found syntopic with L. oblongus. 

The Chemosensory Transcriptome of a Diving Beetle

Insects astoundingly dominate Earth’s land ecosystems and have a huge impact on human life. Almost every aspect of their life relies upon their highly efficient and adaptable chemosensory system. In the air, most chemical signals that are detected at long range are hydrophobic molecules, which insects detect using proteins encoded by multigenic families that emerged following land colonization by insect ancestors, namely the odorant-binding proteins (OBPs) and the odorant receptors (ORs). However, land-to-freshwater transitions occurred in many lineages within the insect tree of life. Whether chemosensory gene repertoires of aquatic insects remained essentially unchanged or underwent more or less drastic modifications to cope with physico-chemical constraints associated with life underwater remains virtually unknown. To address this issue, we sequenced and analyzed the transcriptome of chemosensory organs of the diving beetle Rhantus suturalis (Coleoptera, Dytiscidae). A reference transcriptome was assembled de novo using reads from five RNA-seq libraries (male and female antennae, male and female palps, and wing muscle). It contained 47,570 non-redundant unigenes encoding proteins of more than 50 amino acids. Within this reference transcriptome, we annotated sequences coding 53 OBPs, 48 ORs, 73 gustatory receptors (GRs), and 53 ionotropic receptors (IRs). Phylogenetic analyses notably revealed a large OBP gene expansion (35 paralogs in R. suturalis) as well as a more modest OR gene expansion (9 paralogs in R. suturalis) that may be specific to diving beetles. Interestingly, these duplicated genes tend to be expressed in palps rather than in antennae, suggesting a possible adaptation with respect to the land-to-water transition. This work provides a strong basis for further evolutionary and functional studies that will elucidate how insect chemosensory systems adapted to life underwater.

Integrative taxonomic review of the genus Peschetius (Coleoptera, Dytiscidae, Hydroporinae) from India with description of two new species

The diving beetle genus Peschetius Guignot, 1942 (Coleoptera: Dytiscidae) in India is reviewed. Integrative taxonomic approach using morphology, multivariate morphometry and genetic analysis of cytochrome oxidase subunit 1 revealed the presence of four species, two of which are described here as new: Peschetius bistroemisp. nov. from southern Western Ghats (Kerala) differs from all known congeners with distinctly broadened male antennomeres IV and V, shape of the prosternal process and the male genitalia; P. nilssonisp. nov. from northern Western Ghats, Rajasthan and Madhya Pradesh is similar to the widespread Indian P. toxophorus Guignot, 1942, from which it differs in habitus, elytral colour pattern and the shape of the male genitalia. New records are presented for the remaining Indian species, namely P. quadricostatus (Aubé, 1838) and P. toxophorus. All species are diagnosed, illustrated and a key to their identification is provided.

First records of the diving beetles Hydrovatus subrotundatus Motschulsky, 1859 and Hydrovatus pudicus (Clark, 1863) in Taiwan (Coleoptera, Dytiscidae, Hydroporinae, Hydrovatini)

We provide the first records of the diving beetles Hydrovatus subrotundatus Motschulsky, 1859 and Hydrovatus pudicus (Clark, 1863) from Taiwan. They are otherwise widespread in Southeast Asia. The habitats of both species and the associated diving beetle fauna are briefly described. Altogether eight species of the genus Hydrovatus are now recorded from Taiwan, raising the number of Taiwanese dytiscid species to 68.

First record of the diving beetle Copelatus chevrolati Aubé, 1838 in Cuba (Coleoptera, Dytiscidae, Copelatinae)

We present the first distributional record of Copelatus chevrolati Aubé, 1838 from Cuba. Four specimens were collected in a light trap in August 2016 on the Isla de La Juventud. Ten species of Copelatus are now known from Cuba. We present a modified key to the Cuban species of Copelatus.

Observation and analysis of diving beetle movements while swimming

The fast swimming speed, flexible cornering, and high propulsion efficiency of diving beetles are primarily achieved by their two powerful hind legs. Unlike other aquatic organisms, such as turtle, jellyfish, fish and frog et al., the diving beetle could complete retreating motion without turning around, and the turning radius is small for this kind of propulsion mode. However, most bionic vehicles have not contained these advantages, the study about this propulsion method is useful for the design of bionic robots. In this paper, the swimming videos of the diving beetle, including forwarding, turning and retreating, were captured by two synchronized high-speed cameras, and were analyzed via SIMI Motion. The analysis results revealed that the swimming speed initially increased quickly to a maximum at 60% of the power stroke, and then decreased. During the power stroke, the diving beetle stretched its tibias and tarsi, the bristles on both sides of which were shaped like paddles, to maximize the cross-sectional areas against the water to achieve the maximum thrust. During the recovery stroke, the diving beetle rotated its tarsi and folded the bristles to minimize the cross-sectional areas to reduce the drag force. For one turning motion (turn right about 90 degrees), it takes only one motion cycle for the diving beetle to complete it. During the retreating motion, the average acceleration was close to 9.8 m/s2 in the first 25 ms. Finally, based on the diving beetle's hind-leg movement pattern, a kinematic model was constructed, and according to this model and the motion data of the joint angles, the motion trajectories of the hind legs were obtained by using MATLAB. Since the advantages of this propulsion method, it may become a new bionic propulsion method, and the motion data and kinematic model of the hind legs will be helpful in the design of bionic underwater unmanned vehicles.

Description of the second- and third-instar larvae of Hydrovatus crassulus Sharp, 1882 (Coleoptera: Dytiscidae: Hydrovatini)

The second- and third-instar larvae of the diving-beetle species Hydrovatus crassulus Sharp, 1882 are described and illustrated, including detailed morphometric and chaetotaxic analyses of the cephalic capsule, head appendages, legs, last abdominal segment and urogomphi. Larvae of this species lack the parietal pore PAo, the premental seta LA3 and the urogomphal seta UR8, and have the sensillum MN2 shaped as a short hair-like seta and the ventral surface of the abdominal segments II–V sclerotized. All these characteristics are shared with the other species of Hydrovatus Motschulsky, 1853 known in detail (H. caraibus Sharp, 1882) and therefore are considered diagnostic for the genus. Hydrovatus crassulus also characterizes by the presence of a small galea, which reinforces the hypothesis that this structure is part of the ancestral condition of Hydrovatus. Larvae of H. crassulus differ from those of H. caraibus in having a smaller size, a smaller ratio U/LAS, and a larger ratio U1/U2, and also in the presence (in most cases) of a secondary seta on the anteroventral surface of femur.