Responses of the infrared sensilla of Melanophila acuminata (Coleoptera: Buprestidae) to monochromatic infrared stimulation

The pit organs of the beetle Melanophilaacuminata were stimulated with monochromatic infrared radiation using a continuous wave CO overtone infrared laser. Best sensitivity was in the wavelength range 2.8–3.5 μm. In this range a stimulus intensity of 14.7 mW cm⁻² was sufficient to generate single action potentials. At a wavelength of 5 μm receptor performance significantly decreased. An increase in stimulus intensity caused a decrease in response latency and an increase in the number of action potentials elicited. At a given wavelength (3.4 μm) the dynamic amplitude range of action potential responses covered 12 dB. At high stimulus intensities (94.2 mW cm⁻²) a stimulus duration of 4 ms was sufficient to generate one to two action potentials and a stimulus duration of 60 ms already caused response saturation (with up to nine action potentials). In a repetitive stimulus regime distinct receptor potentials were visible up to a frequency of 600 Hz. Accepted: 18 March 2000     

The photomechanic infrared receptor for the detection of forest fires in the beetle Melanophila acuminata (Coleoptera: Buprestidae)

We recorded from single units of individual sensilla of the thoracic infrared (IR) pit organs of Melanophila acuminata. When the organ was stimulated with a thermal radiator whose emission spectrum was similar to that of a typical forest fire, units responded phasically with up to seven spikes within 30–40 ms at a radiation power of 24 mW cm⁻². In the experiments all wavelengths shorter than 1.6 μm were excluded by a longpass IR filter. Response latencies were about 4 ms and initial impulse frequencies were up to 250 impulses per second (ips). A single spike could be generated even when stimulus duration was only 2 ms. Reduction of total radiation power from 24 mW cm⁻² to 5 mW cm⁻² resulted in increased response latencies of 5–6 ms and the occurrence of only two to three spikes. Initial impulse frequencies decreased to 125 ips. According to our physiological results and calculations, Melanophila should be able to detect a 10-hectare fire from a distance of 12 km. Mechanical stimuli also evoked responses of the IR sensilla. All present morphological and physiological findings lead to the conclusion that the IR receptors of Melanophila must function by means of a hitherto undescribed photomechanic mechanism. Accepted: 1 November 1997     

Electrophysiological characterization of the multipolar thermoreceptors in the "fire-beetle" Merimna atrata and comparison with the infrared sensilla of Melanophila acuminata (both Coleoptera,Buprestidae)

A thermosensitive multipolar neuron innervates each of the four abdominal receptors of the Australian buprestid beetle Merimna atrata. The neuron is spontaneously active within a broad range of body temperatures (tested between 10°C and 40°C). We heated the receptors with a red diode laser (=0.66 µm) at intensities ranging from 5.3 mW cm^–2 up to 1.3 W cm^–2. In general, warming caused an increase of receptor activity. Peak discharge frequencies were reached 100–300 ms after onset of irradiation. After peak frequencies were reached, distinct adaptation took place within seconds. A linear increase in irradiation intensity caused an exponential increase in peak frequencies. Lowest threshold was found to be at 40 mW cm^–2 where latencies were 47 ms. At the highest intensity tested (1.3 W cm^–2), peak frequencies increased up to about 300 Hz and latencies decreased to 24 ms. Considering the pyrophilous behaviour of Merimna and the morphological data from previous studies, our results support the hypothesis that the abdominal receptors are infrared receptors. We also recorded the responses of the photomechanic infrared sensilla of Melanophila acuminata under the same experimental conditions. These results show that the photomechanic sensillum of Melanophila has a higher sensitivity, and that the latencies are considerably shorter.     

Sensitivity threshold and response characteristics of infrared detection in the beetle Melanophila acuminata (Coleoptera: Buprestidae)

The minimum detection threshold of the infrared sensitive beetle, Melanophila acuminata, was measured with a helium-neon laser that emitted light at a wavelength of 3.39 microm. Extracellular recordings were taken both at the pit organ responsible for detection and at the interganglionic connectives in the thorax of the beetle. At the pit organ, generator and action potentials from single neurons were measured with a sharpened tungsten electrode. At the connectives that linked the fused second meso-/metathoracic and prothoracic ganglia, compound action potentials were measured with a tungsten hook electrode that encircled the connective. The latter recordings confirmed conveyance of infrared information through specific pathways to rostrally-situated sites in the nervous system of the beetle. The 50% probability irradiance threshold at which action potentials were elicited from the receptor and connectives occurred at 17.3 and 14.6 mW/cm(2), respectively. In addition to sensitivity threshold, several other characteristics of the response were quantified including dependence of generator potential latency, generator potential duration, spike frequency, and spike latency on irradiance, dependence of response strength (spike count) on exposure time, and flicker fusion frequency. The ability to detect infrared radiation is rare in nature, and these results provide valuable information necessary to understand this unique sensitivity.     

Thermomechanical properties of the stimulus transducing cuticle in the infrared organ of Merimna atrata (Coleoptera,Buprestidae)

The pyrophilous Australian “fire‐beetle” Merimna atrata strongly depends on the occurrence and localization of forest fires for its reproduction. As a special adaptation to its unusual biology, elaborate infrared (IR) organs have evolved in this species. The IR‐organs consist of a specialized cuticular portion, the absorbing area, innervated by a sensory complex. The sensory complex contains a thermosensitive multipolar neuron with a specialized dendritic region, the terminal dendritic mass, and a mechanosensitive unit represented by a chordotonal organ (CO). Evidence for the IR‐receptive function so far has only been provided for the multipolar neuron. Based on morphological data, it has been hypothesized that the CO could also be involved in IR‐reception by measuring minute thermal deformations of the absorbing area. To test this hypothesis, we investigated structural features like cuticle thickness, reduced Young's modulus and hardness of the absorbing area. The results were used in finite element simulations to analyze the thermomechanical behavior and performance of the IR‐organ. Our findings indicate that considerable thermal deformation of the absorbing area occurs, supporting the hypothesis that the CO could function as photomechanical IR‐receptor. Interestingly, at the innervation site of the CO the lowest relative displacements of the absorbing area were found. This may indicate that the CO as putative photomechanic IR‐receptor has not been adapted according to the requirements of highest sensitivity. Probable benefits of the bimodal innervation by a thermosensory and a mechanosensory unit and their possible interaction for an improved performance of the IR‐organ are discussed. J. Morphol. 275:991–1003, 2014. © 2014 Wiley Periodicals, Inc.     

Chemotactic responses of the ladybeetle Harmonia axyridis (Coleoptera: Coccinellidae) to volatile compounds from the scale insect Drosicha corpulenta (Hemiptera: Coccoidea: Monophlebidae) and its host plant

The ladybeetle Harmonia axyridis Pallas (Coleoptera: Coccinellidae), is a key predator of the scale insect Drosicha corpulenta (Kuwana), (Hemiptera: Coccoidea: Monophlebidae) in persimmon tree orchards. We used a Y-tube olfactometer and gas chromatograph/mass spectrometry to assess the possible role of volatiles from persimmon trees in attracting H. axyridis. The results showed more ladybeetles aggregated at odour sources from heavily damaged trees than from slightly damaged or undamaged trees. The relative amounts and types of terpenoid and alcohol compounds changed, usually increased, in the volatiles from damaged persimmon trees: α-pinene increased from 26 to 43%. The ladybeetle was attracted to α-pinene in a Y-tube assay at most tested concentrations.     

Back from extinction: Rediscovery of the Canterbury knobbled weevil Hadramphus tuberculatus (Pascoe 1877) (Coleoptera: Curculionidae), with a review of its historical distribution

Abstract

The Canterbury knobbled weevil, Hadramphus tuberculatus (Coleoptera: Curculionidae: Molytini), was once widespread in the Canterbury plains, foothills and fringing ranges, ranging from Oxford in the north to Waimate in the south. Habitat degradation, reduction in host plant numbers through grazing and predation by rodents are thought to be responsible for the decline in its numbers and distribution. In December 2004, more than 80 years since the last sighting of H. tuberculatus in 1922, a single individual was found at Burkes Pass Scenic Reserve. This paper records the rediscovery of H. tuberculatus, reviews the historical distribution records for H. tuberculatus, discusses them with respect to changes in host plant habitat in the eastern South Island, and suggests conservation strategies to protect this and other relictual populations that might be found in future.