Microscale Gaseous Slip Flow in the Insect Trachea and Tracheoles.

An analytical investigation into compressible gas flow with slight rarefactions through the insect trachea and tracheoles during the closed spiracle phase is undertaken, and a complete set of asymptotic analytical solutions is presented. We first obtain estimates of the Reynolds and Mach numbers at the channel terminal ends where the tracheoles directly deliver respiratory gases to the cells, by comparing the magnitude of the different forces in the compressible gas flow. The 2D Navier-Stokes equations with a slip boundary condition are used to investigate compressibility and rarefied effects in the trachea and tracheoles. Expressions for the velocity components, pressure gradients and net flow inside the trachea are then presented. Numerical simulations of the tracheal compressible flow are performed to validate the analytical results from this study. This work extends previous work of Arkilic et al. (J Microelectromech Syst 6(2):167-178, 1997) on compressible flows through a microchannel. Novel devices for microfluidic compressible flow transport may be invented from results obtained in this study.

Gas Exchange Models for a Flexible Insect Tracheal System.

In this paper two models for movement of respiratory gases in the insect trachea are presented. One model considers the tracheal system as a single flexible compartment while the other model considers the trachea as a single flexible compartment with gas exchange. This work represents an extension of Ben-Tal's work on compartmental gas exchange in human lungs and is applied to the insect tracheal system. The purpose of the work is to study nonlinear phenomena seen in the insect respiratory system. It is assumed that the flow inside the trachea is laminar, and that the air inside the chamber behaves as an ideal gas. Further, with the isothermal assumption, the expressions for the tracheal partial pressures of oxygen and carbon dioxide, rate of volume change, and the rates of change of oxygen concentration and carbon dioxide concentration are derived. The effects of some flow parameters such as diffusion capacities, reaction rates and air concentrations on net flow are studied. Numerical simulations of the tracheal flow characteristics are performed. The models developed provide a mathematical framework to further investigate gas exchange in insects.

The role of the subelytral cavity in respiration in a tenebrionid beetle, Onymacris multistriata (Tenebrionidae: Adesmiini).

This study measured the respiratory patterns in the tenebrionid beetle, Onymacris multistriata, using flow-through respirometry to measure carbon dioxide emission from the mesothoracic spiracles separately and simultaneously with that from around the elytral case. 96% of the total CO(2) emitted was via the mesothoracic spiracles. These spiracles used a discontinuous gas exchange cycle similar to that measured from other tenebrionid beetles. Although the circadian rhythm of the beetles resulted in changes to the period durations and cycle frequencies in the discontinuous gas exchange cycles, the mesothoracic spiracle remained the major site for gas exchange. Thus the subelytral cavity plays a different role in respiration other than the elimination of CO(2) build-up. It is expected that other arid dwelling flightless beetles will also be shown to use the mesothoracic spiracle as the major route for CO(2) emission.

Discontinuous gas exchange in dung beetles: patterns and ecological implications.

This study correlates a distinctive pattern of external gas exchange, referred to as the discontinuous gas exchange cycle (DGC), observed in the laboratory, with habitat associations of five species of telecoprid dung beetles. The beetles were chosen from a variety of habitats that would be expected to present different amounts of water stress. All five species exhibited DGC. Sisyphus fasciculatus has been recorded only in woodland areas, and does not have strict spiracular control during its DGC. Anachalcos convexus and Scarabaeus rusticus are associated with open mesic habitats. Both species exhibit a distinct DGC, previously found in some other insect species, but intermediate within this study group. Sc. flavicornis and Circellium bacchus are typically found in arid regions, and have the most unusual form of DGC, with spiracular fluttering during the burst phase. These results support the hypothesis that spiracular fluttering reduces respiratory water loss. From this study we conclude that the DGC is an ancestral adaptation, most probably as a result of anoxic environments in underground burrows, but that spiracular control is enhanced to reduce respiratory water loss in beetle species that live in arid habitats.

The ponerine ant Pachycondyla (=Ophthalmopone) berthoudi Forel carries loads economically.

The energy cost of running and carrying a load were measured in the termitophagus ponerine ant Pachycondyla (=Ophthalmopone) berthoudi. This ant species uses the individual foraging method in which there is no cooperation between the foragers in the search for or retrieval of prey items. The foragers also transport workers and brood between the nests of the polydomous colony. Pachycondyla berthoudi foragers ran voluntarily in a running tube respirometer at 25 degrees C. Some of the foragers ran in the running tube carrying their termite load, which enabled the metabolic costs of carrying immobilized prey to be determined. This included the costs of maintaining the prey in the mandibles and of stabilization during running. The minimum cost of unladen running was 165.9 J kg-1 m-1, while that of laden running was 136.1 J kg-1 m-1. The mass used to calculate the cost of laden running included body mass of ant and mass of load carried. Pachycondyla berthoudi foragers carry their loads very cheaply. Load carriage costs were calculated to be about 40% as much as body carriage per unit mass, which is the lowest yet found for ants. Low cost of load carriage could have been selected for in P. berthoudi due to its life history.

Respiratory gas exchange in the tick Amblyomma hebraeum (Acari: Ixodidae).

Respiratory gas exchange was studied in unfed adult Amblyomma hebraeum Koch. Carbon dioxide emission was measured at 25 degrees C using flow-through respirometry to determine standard metabolic rate and the temporal pattern of gaseous emission. The standard CO2 production rate (sVCO2) of inactive ticks was 0.0135 +/- 0.0085 ml g-1 h-1, and the standard O2 consumption rate (sVO2) was 0.0158 +/- 0.0097 ml g-1 h-1. Ventilation was discontinuous and was characterized by periodic bursts of CO2 emissions at frequencies of 0.33 h-1-1.11 h-1. Low metabolic rate coupled with discontinuous ventilation may contribute to the ability of adult A. hebraeum to withstand prolonged periods of starvation and desiccation in the absence of a host.

Ventilation in the adults of Amblyomma hebraeum and A. marmoreum (Acarina, Ixodidae), vectors of heartwater in southern Africa.

The objective of this study was to establish the major features of respiratory gas exchange in unfed adults of the ticks Amblyomma hebraeum and A. marmoreum, both vectors of heartwater in Southern Africa. Carbon dioxide emission of ticks was measured at 25 degrees C using flow-through respirometry in order to determine standard metabolic rate (SMR) and the temporal pattern of gaseous emission. For both species, SMR was extremely low and approximately 100 fold less than that predicted for an insect of equivalent body mass. Ventilation in inactive ticks was discontinuous and characterized by periodic bursts of CO2 emissions during spiracular opening. The main selective advantage of this type of ventilation is believed to lie in a reduction of respiratory water loss. The periodicity of CO2 bursts was less frequent in A. marmoreum (every 2.5 h) compared to A. hebraeum (every 1.5 h) suggesting that A. marmoreum is more efficient at conserving respiratory water loss. It is suggested that future research into water balance physiology of ticks should address the role of ventilatory patterns in determining off-host survival and habitat associations.