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< Leonid I. Frantsevich >

Leonid Frantsevich

Experimental evidence on actuation and performance of the elytron-to-body articulation in a diving beetle, Cybister laterimarginalis (Coleoptera, Dytiscidae).

Journal of Insect Physiology, 2012, 58: 1650Ц1662.

Doi: http://dx.doi.org/10.1016/j.jinsphys.2012.10.006.

Movements of the elytra and axillary sclerites were video recorded in tethered flying beetles and in manipulated mounts of C. laterimarginalis, Dytiscus dimidiatus, and Acilius sulcatus. Mesothoracic axillary plates are homologues of those in the metathorax. Two anterior axillaries (Ax1, Ax2) fuse together; they are hinged to the third axillary plate (Ax3). In turn, Ax3 is hinged with the elytron. During take-off, a beetle abducts and highly elevates its elytra (1), then droops the elytra in a flatly spread position (2); closing is adduction in a horizontal plane (3). These steps have been simulated: (1) by pressing down the anterior horn; (2) occurred spontaneously after release of pressing; (3) the elytron closed flatly either by manual turn of the elytron or by manual elevation of the prothorax. Anterior axillaries rotated forward and down during (1), returned during (2) and remained immobile during closing. Ax3 is folded between the closed elytron and Ax1+Ax2; it unfolds during opening. Two hinges of Ax3 form a Z-configuration and provide a linked drive for complicated rotation of the elytron. Opening was impaired in vivo if tergal leg protractor and depressor were disabled, closing did not suffer. Closing was prevented by excision in the hind edge of the pronotum, not harmful for opening. Role of direct and indirect muscles in transient elytral movements is discussed.


Opening and closing of elytra in a tethered Cybister laterimarginalis. Selected frames from a video film, time in italics. Neighbour frames in rows. A straw rod glued normally to the prothorax indicates its orientation relative to the fixed pterothorax. The initial orientation is indicated with a thin white line in (0.00 s) and copied in (0.56 s), indicating depression of the prothorax during opening. Elevation of the prothorax during closing is shown in (2.12 and 2.44 s) in the same fashion. Alternating elevations and depressions of the spread elytra are indicated with arrows in serial frames.


Trajectory of apical marks on the elytra in Cybister laterimarginalis during opening and closing. Top panel Ц frontal body-fixed plane, bottom panel Ц equatorial plane. Tip of the scutellum is the origin of body-fixed reference. Scales in mm. Elytra are elevated higher during opening.

Reconstruction of the structure and performance of the elytral articulation must explain peculiarities of elytral movements in diving beetles.


(A) Elytron in C. laterimarginalis, ventral face. Articulatory root area in a box.

(B) Root area, dorsal face, (C) ventral face.

Circles e2, e3 Ц articulations with elytral processes of axillaries 2 and 3, h Ц head of Ax1, LA, MA Ц lateral and medial apophyses of the root.

Homology between elytral and wing axillary plates Ax1-Ax3a. Abbreviations: c1 Ц crease between Ax2 and Ax3; e Ц elytral processes to the root; v Ц ventral subplate of Ax2.


(click on the image to view movie in separate window)

Microfilming of dead mount of C. laterimarginalis. Front view at the right elytron and mesothorax. (sctl Ц scutellum)

Manipulated opening of the right elytron by pressing onto the anterior horn (AH) simulates contraction of the direct tergo-pleural muscle M33 and indirect leg protractor and depressor. Anterior axillaries Ax1, Ax2 rotate together with the elytron, the elytron elevates. The open elytron falls down. Manipulated closing was achieved by turn of the elytral blade with a forceps. Anterior axillaries remain immobile.

Direct and indirect mesothoracic wing muscles in Cybister laterimarginalis. Whole mounts in glycerol, dark field photographs. Muscle numbers by Larsen (1946). Scale square: 1 mm2.
M40a, c Ц leg retractors.
M33 Ц direct opener of the elytron.
M36a Ц direct closer ?
Muscles of dual function:
M39 Ц leg protractor, opener.
M47 Ц leg depressor, opener.
M39 Ц leg retractor, closer.


(click on the image to view movie in separate window)

Microfilming of dead mount of C. laterimarginalis. Right side, rear view.

Rotation of Ax3 upon manipulated closing and opening by the blade of the elytron. Creases C1 and C2 fold or unfold. Anterior axillaries Ax1, Ax2 remain immobile. Double rotation about two creases provides a linked drive with the single degree of freedom.


(click on the image to view movie in separate window)

Manipulated closing by the prothorax in C. laterimarginalis simulates contraction of muscles elevating the head and prothorax. The posterior edge of the pronotum acts on the root of the elytron.


(click on the image to view movie in separate window)

High opening, flutter, and flat closing in Dytiscus dimidiatus.


(click on the image to view movie in separate window)

Abortive opening and normal closing of the left elytron in Acilius sulcatus after excision of the left midleg and inactivation of indirect leg protractor and depressor.


Collection of films:

Courtship dances in a fly, Lispe spp.

Stick friction in a lantern fly, Lycorma delicatula

Arolium of a hornet, Vespa crabro

Indirect closing of elytra in a cockchafer, Melolontha

Righting kinematics in beetles (Insecta: Coleoptera)

Leg coordination during turning on an extremely narrow substrate in a bug, Mesocerus marginatus (Heteroptera, Coreidae)

Swimming in the Diving Wasp Prestwichia aquatica (Hymenoptera: Trichogrammatidae)

Kinematics of elytra in beetles

Indirect closing of elytra in various beetles

Double rotation of the opening (closing) elytra in beetles (Coleoptera)

Actuation and performance of the elytron-to-body articulation in a diving beetle


I. I. Schmalhausen Institute of Zoology, 2004-2009