Acanthocnemus Research Articles

New Records of Acanthocnemus nigricans (Hope, 1843) (Coleoptera, Acanthocnemidae) in European Russia

New records of the pyrophilous beetle of Australian origin, Acanthocnemus nigricans (Hope, 1843), which was first recorded from Russia in 2010, are reported. Distribution and the possible prospects of the invasion are discussed.

Function Modeling of the Infrared Organ of “Little Ash Beetle” Acanthocnemus Nigricans (Coleoptera, Acanthocnemidae)

Acanthocnemus nigricans is an inconspicuous pyrophilous beetle that approaches forest fires. The beetle is equipped with a pair of unique infrared (IR) receptors on its prothorax that allows it to detect hot surfaces in flight. The IR receptor consists of a little disc bearing about 90 tiny sensilla on its anterior half. The disc sensilla are unique in insects and their functions are largely unknown. Using a 3D reconstruction of the head and thorax we performed case studies to reveal different position-dependent expositions of the IR receptors to incoming radiation. Results show that the spatiotemporal pattern in which different sectors of the disc are exposed provides the beetle with unambiguous information about its current direction to an IR source. As a striking structural element, the disc sensilla contain an electron-dense rod connecting an outer peg to the inner sensory cell. Finite element simulations suggest that the rod serves as a heat conductor directing heat to the thermosensitive cell inside the disc. Thus the disc sensilla can be interpreted as discrete temperature reading points. The resulting pattern of stimulated/deactivated sensilla, therefore, could provide the flying beetle with spatiotemporal information about its current position relative to an IR source. Possible biomimetic perspectives of the findings are discussed.

Volatile Combustion Products of Wood Attract Acanthocnemus nigricans (Coleoptera: Acanthocnemidae)

Acanthocnemus nigricans is an Australian pyrophilic beetle approaching smoldering logs for mating and oviposition. We investigated the behavior of the beetles towards combustion products of cellulose (5-methylfurfural, hydroxacetone, karrikinolide), lignin (4-methylguaiacol, 4-ethylguaiacol, eugenol), and (Z)-3-hexen-1-ol in a custom built dynamic two arm olfactometer. The beetles were attracted by 5-methylfurfural, 4-methylguaiacol, 4-ethylguaiacol, eugenol, and hydroxyacetone at different concentrations. Abundances of beetles caught in traps baited with a mixture of the most attractive volatiles showed only a trend to higher numbers. These results are discussed with respect to weather conditions and complementing infrared perception of the pyrophilic beetles.

Acanthocnemidae (Coleoptera), a family of beetles new to Russia

Acanthocnemus nigricans (Hope, 1843), a single recent representative of the beetle family Acanthocnemidae, is reported from Russia for the first time. Distribution, probable ways of dispersion and the published data on the biology of A. nigricans are discussed.

Electrophysiological characterisation of the infrared organ of the Australian “Little Ash Beetle” Acanthocnemus nigricans (Coleoptera, Acanthocnemidae)

This study characterises the response properties of the sensilla located on the prothoracic disc organ of the beetle Acanthocnemus nigricans, such as intensity response functions and temporal coding properties. Warming the sensilla by a red laser accelerated their ongoing spiking activity, cessation of the stimulus suppressed their firing as revealed by extracellular recordings. Convective heat sources also increased sensillum activity, but stimuli of other modalities failed to elicit responses. The response threshold was between 11 and 25 mW/cm2 and latencies ranged between 20 and 40 ms. Repeating stimuli with frequencies between 5 and 20 Hz were reliably resolved by the sensilla. This temporal resolution enables the disc sensilla to represent behaviourally relevant changes in heat stimuli in a thermally patchy environment. These findings complement our knowledge on the sensory physiology of pyrophilous insects by hinting at two different, elementary orientation strategies evolved in the three pyrophilous beetle species described. A. nigricans seems to be best adapted to short-range orientation on freshly burnt areas.

Morphology of the prothoracic discs and associated sensilla of Acanthocnemus nigricans (Coleoptera, Acanthocnemidae)

The Australian ‘little ash beetle’ Acanthocnemus nigricans (Coleoptera, Cleroidea, Acanthocnemidae) is attracted by forest fires. A. nigricans has one pair of unique prothoracic sensory organs and it has been speculated that these organs may play a role in fire detection. Each organ consists of a cuticular disc, which is fixed over an air-filled cavity. On the outer surface of the disc, about 90 tiny cuticular sensilla are situated. The poreless outer peg of a sensillum is 3–5 μm long and is surrounded by a cuticular wall. One ciliary sensory cell innervates the peg. As a special feature, the outer dendritic segment is very short already terminating below the cuticle. A massive electron-dense cylindrical rod, which most probably represents the hypertrophied dendritic sheath, extends through the cuticular canal connecting the tip of the outer dendritic segment to the peg. The dendritic inner segment and the soma are fused indistinguishably. Thin, leaflike extensions of glial cells deeply extend into that conjoint and considerably enlarged compartment which also contains large numbers of mitochondria. In summary, the sensilla of the sensory disc of A. nigricans represent a new type of insect sensillum of hitherto unknown function. The possible role of the prothoracic sensory organ in fire detection is discussed.

A new type of insect infrared organ of low thermal mass.

The Australian beetle Acanthocnemus nigricans is attracted by forest fires and has a pair of complex infrared (IR) receptor organs on the first thoracic segment. Each organ consists of a tiny sensory disc (diameter 120-130 microm) which serves as an absorbing structure for IR radiation. The disc is arranged above an air-filled cavity which is located just anteriorly to the coxae of the prothoracic legs. Inside the disc, about 30 multipolar thermoreceptors (warmth receptors) are tightly attached to the cuticle which is directed to the outside. The many dendrites of each multipolar neuron are tightly wrapped around the soma and contain a large number of mitochondria. Absorption of IR radiation by the disc causes an increase in temperature which is measured by the warmth receptors. Therefore, the IR receptors of A. nigricans can be classified as microbolometers with reduced thermal mass and in principle can be compared to the IR organs of pit vipers.