Christian Pulver

The ability to substitute peat use in horticulture with potentially more sustainable alternatives hinges on the local availability of suitable biomass resources and whether these resources can be easily processed to achieve similar agronomic effectiveness to peat. This review estimates potential biomass availability in Ireland by reviewing production statistics and industry reports and identifying current uses and hypothetical processed biomass quantities. Annual estimates of the major biomass resources available in Ireland are 488,935 m³ of woody residues (mainly Sitka spruce pine) and 789,926 m³ of arable straws (from oats, wheat, barley, oil seed rape). The potential major processing pathways for the available biomass are mechanical (extruded, thinscrew, hammer milled, disc refined), carbonization (pyrolysis and hydrothermal carbonization) and composting. This review of the literature indicates that the major challenges to pyrolyzed alternatives in growth media include high alkalinity, high salinity and low water holding capacity. When biomass is processed into fibers, it requires additional processing to address nutrient immobilization (nitrogen and calcium) and the presence of phytotoxic compounds. We discuss possible solutions to these challenges in terms of agronomic management (altering fertigation, irrigation rates etc.), biomass conversion process optimization (changing conditions of processes and applying additives) and novel growth media formulations with various material inputs that complement each other. We conclude that while national alternative biomass resources are available in sufficient volumes to potentially meet growing media requirements, significant further research and demonstration are required to convert these materials to growth media acceptable to both commercial and retail sectors. Research needs to focus on transforming these materials into growth media, and how they will impact agronomic management of crops. Furthermore to this, the optimization of biomass conversion processes and novel formulations incorporating multiple types of biomass need to be the focus as we transition from peat products in professional horticulture.

The ability to substitute peat use in horticulture to potentially more sustainable alternatives hinges on the local availability of suitable biomass resources and whether these resources can be easily processed to achieve similar agronomic effectiveness to peat. This review estimates potential bio-mass availability in Ireland by reviewing production statistics and industry reports and identifying current uses and hypothetical processed biomass quantities. Annual estimates of the major biomass resources available in Ireland are 488 935 m3 of woody residues (mainly Sitka spruce pine) and 789 926 m3 of arable straws (from oats, wheat, barley, oil seed rape). The potential major processing pathways for the available biomass are mechanical (extruded, thinscrew, hammer milled, disc re-fined), carbonization (pyrolysis and hydrothermal carbonization) and composting. This review of the literature indicates that the major challenges to pyrolyzed alternatives in growth media include high alkalinity, high salinity and low water holding capacity. When biomass is processed into fibers, it requires additional processing to address nutrient immobilization (nitrogen and calcium) and the presence of phytotoxic compounds. We discuss possible solutions to these challenges in terms of agronomic management (altering fertigation, irrigation rates etc.), biomass conversion process op-timization (changing conditions of processes and applying additives) and novel growth media formulations with various material inputs that complement each other. We conclude that while national alternative biomass resources are available in sufficient volumes to potentially meet growing media requirements, significant further research and demonstration is required to convert these materials to growth media acceptable to both commercial and retail sectors. Research needs to focus on transforming these materials into growth media, and how they will impact agronomic management of crops. Furthermore, the optimization of biomass conversion processes and novel formulations incorporating multiple types of biomass needs to be the focus as we transition from peat products in professional horticulture.

Early predator detection is a key component of the predator-prey arms race and has driven the evolution of multiple animal hearing systems. Katydids (Insecta) have sophisticated ears, each consisting of paired tympana on each foreleg that receive sound both externally, through the air, and internally via a narrowing ear canal running through the leg from an acoustic spiracle on the thorax. These ears are pressure-time difference receivers capable of sensitive and accurate directional hearing across a wide frequency range. Many katydid species have cuticular pinnae which form cavities around the outer tympanal surfaces, but their function is unknown. We investigated pinnal function in the katydid Copiphora gorgonensis by combining experimental biophysics and numerical modelling using 3D ear geometries. We found that the pinnae in C. gorgonensis do not assist in directional hearing for conspecific call frequencies, but instead act as ultrasound detectors. Pinnae induced large sound pressure gains (20–30 dB) that enhanced sound detection at high ultrasonic frequencies (>60 kHz), matching the echolocation range of co-occurring insectivorous gleaning bats. These findings were supported by behavioural and neural audiograms and pinnal cavity resonances from live specimens, and comparisons with the pinnal mechanics of sympatric katydid species, which together suggest that katydid pinnae primarily evolved for the enhanced detection of predatory bats.

Ensiferan orthopterans offer a key study system for acoustic communication and the process of insect hearing. Cyphoderris monstrosa (Hagloidea) belongs to a relict ensiferan family and is often used for evolutionary comparisons between bushcrickets (Tettigoniidae) and their ancestors. Understanding how this species processes sound is therefore vital to reconstructing the evolutionary history of ensiferan hearing. Previous investigations have found a mismatch in the ear of this species, whereby neurophysiological and tympanal tuning does not match the conspecific communication frequency. However, the role of the whole tympanum in signal reception remains unknown. Using laser Doppler vibrometry, we show that the tympana are tonotopic, with higher frequencies being received more distally. The tympana use two key modalities to mechanically separate sounds into two auditory receptor populations. Frequencies below approximately 8 kHz generate a basic resonant mode in the proximal end of the tympanum, whereas frequencies above approximately 8 kHz generate travelling waves in the distal region. Micro-CT imaging of the ear and the presented data suggest that this tonotopy of the tympana drive the tonotopic mechanotransduction of the crista acustica (CA). This mechanism represents a functional intermediate between simple tuned tympana and the complex tonotopy of the bushcricket CA.

Early predator detection is a key component of the predator-prey arms race, and has driven the evolution of multiple animal hearing systems. Katydids (Insecta) have sophisticated ears, each consisting of paired tympana on each foreleg that receive sound directly externally, and internally via a narrowing ear canal through the acoustic spiracle. These ears are pressure-time difference receivers capable of sensitive and accurate directional hearing across a wide frequency range, despite the small size of katydids. Many katydid species have cuticular pinnae which form cavities around the outer tympanal surfaces, but their function is unknown. We investigated pinnal function in the katydid Copiphora gorgonensis by combining experimental biophysics and numerical modelling using 3D ear geometries. Results show that the pinnae in C. gorgonensis do not assist in directional hearing for specific call frequencies, but instead pinnae act as ultrasound detector devices. Pinnae induced large sound pressure gains that enhanced sound detection at high ultrasonic frequencies (> 60 kHz), matching the echolocation range of co-occurring insectivorous bats. Comparing pinnal mechanics of sympatric katydid species supports these findings, and suggests that pinnae evolved in katydids primarily for enhanced predator detection. Audiograms (both behavioural and neural) and tympanal cavity resonances obtained from living specimens corroborate our findings.

The use of acoustics in predator evasion is a widely reported phenomenon amongst invertebrate taxa, but the study of ultrasonic anti-predator acoustics is often limited to the prey of bats. Here, we describe the acoustic function and morphology of a unique stridulatory structure – the Ander9s organ – in the relict orthopteran Cyphoderris monstrosa (Ensifera, Hagloidea). This species is one of just eight remaining members of the family Prophalangopsidae, a group with a fossil record of over 90 extinct species widespread during the Jurassic period. We reveal that the sound produced by this organ has the characteristics of a broadband ultrasonic anti-predator defence, with a peak frequency of 58±15.5 kHz and a bandwidth of 50 kHz (at 10 dB below peak). Evidence from sexual dimorphism, knowledge on hearing capabilities and assessment of local predators, suggests that the signal likely targets ground-dwelling predators. Additionally, we reveal a previously undescribed series of cavities underneath the organ that probably function as a mechanism for ultrasound amplification. Morphological structures homologous in both appearance and anatomical location to the Ander9s organ are observed to varying degrees in 4 of the 7 other extant members of this family, with the remaining 3 yet to be assessed. Therefore, we suggest that such structures may either be more widely present in this ancient family than previously assumed, or have evolved to serve a key function in the long-term survival of these few species, allowing them to outlive their extinct counterparts.

Transparency is a greatly advantageous form of camouflage, allowing species to passively avoid detection regardless of the properties of the surface which they occupy. However, it is uncommon and poorly understood in terrestrial species. In one tribe of predacious katydids (Phlugidini), transparency is paired with highly ultrasonic communication for increased predator evasion, yet little is known about the singing capabilities of these species, with only one genus of Phlugidini acoustically well described to date. Here, we describe Speculophlugis hishquten; a new monotypicgenus of highly transparent crystal katy did here named after the infamous Hish-Qu-Ten from the Predator film franchise, discussing the potential use of this species for non-invasive studies of internalanatomy, and analysing its ultrasonic call. Using laser Doppler vibrometry and light microscopy techniques, we found the transparency of the cuticle around the hearing apparatus to be 85–87% at the wavelength of the laser beam (633 nm), making S. hishquten a candidate for the highest recorded cuticle transparency of any insect. The male song has a fundamental frequency of 50 kHz, matching both the ultrasonic call range and rapid call structure of other Phlugidini species. However, the extent of ultrasonic communication and the level of transparency across the Phlugidini tribe requires more attention.