Leonid Frantsevich
Indirect closing of elytra by the prothorax
in beetles (Coleoptera): general observations and exceptions
Journal of Zoology (2012) 115: 12-21.
Voluntary movements of the prothorax and the elytra in tethered
flying beetles and manually induced movements of these parts in
fresh dead beetles were recorded in 30 species representing 14
families. Participation of prothoracic elevation in the closing
of the elytra was demonstrated in three ways. (i) The elevation
was always simultaneous with elytral closing, in contrast to depression
and elytral opening; a rare exception occurred in Lucanus cervus,
whose elytra sometimes started to close before the cessation of
wing strokes and the elevation of the prothorax. (ii) The manipulated
elevation always induced closing of the spread elytra; the mechanical
interaction between the hind edge of the pronotum and the roots
of the elytra is a universal mechanism of closing the elytra in
beetles. (iii) The prevention of pronoto-elytral contact in live
beetles by the excision of the hind edge of the pronotum in front
of the root prevented elytral closing after normal flight. Exceptions
to this rule included some beetles that were able to close their
elytra after such an excision: tiger beetles and diving beetles
(seldomly) and rose chafers (always). This ability in Adephaga
may be explained by attachments of the muscle actuating the 4th
axillary plate, which differ from the attachments in Polyphaga.
Cetoniinae open their elytra only by a small amount. It is proposed
that their small direct adductors in combination with the elasticity
of the sclerites are enough to achieve elytral closing without
additional help from the prothorax.
Coordination between the prothorax and the elytra
in a tiger beetle
Coordination between the elevation
α of the prothorax (see direction of a rod glued to the pronotum)
and elevation ε of the elytron (see direction of the costal edge)
in Cicindela hybrida. Six short flight bouts traced in
two films.
Manipulated closing by the elevation of the prothorax
in a dead leaf beetle Chrysomela sanguinolenta
Manipulated closing by the elevation
of the prothorax in a dead rose chafer
Potosia aeruginosa
Prevention of closing after excision in the hind
edge of the pronotum in front of the right elytron
Excision in the hind edge
of the pronotum in front of the right elytron in a potatoe beetle
Leptinotarsa 10-lineata
A potatoe beetle Leptinotarsa
10-lineata is unable to close the right elytron after the
excision of a piece of the pronotum in front of the right elytron
Excision on the posterior edge of the pronotum
in front of the right elytron hinders closing in Leptinotarsa
decemlineata. (А) stages of a flight episode in one specimen:
(1) before opening, (2) flight, (3) finish of closing. (B-E) finish
of closing in other four specimens. Selected frames from video
films.
Tiger beetles Cicindela hybrida suffer difficulties
with the closing after the excision of a piece in front of the
right root
Rose chafers do not suffer after such excision
Mesothoracical wing muscles in Adephaga
(Cybister)
and Polyphaga (Prionus, Cetonia).
Flat projections onto the frontal
plane. Sclerites are spaced, real proportions of some muscles
may be distorted. Axillary plates are painted red.
Direct closer M43 in Adephaga inserts
onto the coxa, its analog M35 in Polyphaga - onto the articulatory
membrane above the spiracle. Muscles subserving both legs and
wings M39 and M47 in Adephaga originate from the tergite, their
analogs M42 and M50 in Polyphaga insert onto the first axillary
plate.
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