Spiracle activity in moth pupae—The role of oxygen and carbon dioxide revisited

After decades of intensive research, the actual mechanism behind discontinuous gas exchange in insects has not been fully understood. One open question concerns the actual way (closed, flutter, and open) of how spiracles respond to tracheal gas concentrations. As the results of a classic paper [Burkett, B.N., Schneiderman, H.A., 1974. Roles of oxygen and carbon dioxide in the control of spiracular function in cecropia pupae. Biological Bulletin 147, 274-293] allow ambiguous interpretation, we thus reexamined the behavior of the spiracles in response to fixed, controlled endotracheal gas concentrations.The tracheal system of diapausing pupae of Attacus atlas (Saturniidae, Lepidoptera) was flushed with gas mixtures varying in PO₂ and PCO₂ while the behavior of the spiracles was monitored using changes in the pressure signal. This novel pressure based technique proved to be superior to classic visual observation of single spiracles. A two-dimensional map of the spiracle behavior in response to endotracheal PO₂ and PCO₂ was established. Typically, it contained two distinct regions only, corresponding to “closed” and “open” spiracles. A separate “flutter” region was missing. Because fluttering is commonly observed in moth pupae, we suggest that the intermittent spiracle opening during a flutter phase is an effect of non-steady-state conditions within the tracheal system. For low PCO₂ the minimum PO₂ resulting in open spiracles was linearly dependent upon PCO₂. Above a threshold of 1-1.5 kPa CO₂ the spiracles were open irrespective of PO₂. We propose a hypothetical spiracular control model, which is simple and explains the time course of endotracheal partial pressures during all phases of discontinuous gas exchange.     

Tracheal compression in pupae of the beetle Zophobas morio

Insects that are small or exhibit low metabolic rates are considered to not require active ventilation to augment diffusive gas exchange. Some pupae with low metabolic rates exhibit abdominal pumping, a behaviour that is known to drive tracheal ventilation in the adults of many species. However, previous work on pupae suggests that abdominal pumping may serve a non-respiratory role. To study the role of abdominal pumping in pupa of the beetle Zophobas morio, we visualized tracheal dynamics with X-rays while simultaneously measuring haemolymph pressure, abdominal movement, and CO₂ emission. Pupae exhibited frequent tracheal compressions that were coincident with both abdominal pumping and pulsation of pressure in the haemolymph. However, more than 63% of abdominal pumping events occurred without any tracheal collapse and hence ventilation, suggesting that the major function of the abdominal pump is not respiratory. In addition, this study shows that the kinematics of abdominal pumping can be used to infer the status of the spiracles and internal behaviour of the tracheal system.     

Neural control of homologous behaviour patterns in two blaberid cockroaches

Activity patterns of motoneurones which innervate spiracular muscles in two blaberid cockroaches, Blaberus discoidalis and Gromphadorhina portentosa, have been monitored during two homologous behaviour patterns: respiratory and non-respiratory tracheal ventilation. Based upon the activity of spiracular motoneurones during these two activities, the abdominal spiracles have been divided into three functional groups: vestigial, respiratory and non-respiratory. In Blaberus discoidalis spiracle 3 is vestigial, spiracles 6, 7, 8 and 10 are respiratory, and spiracles 4, 5 and 9 are non-respiratory. In Gromphadorhina portentosa spiracles 3 and 10 are vestigial, spiracle 4 is non-respiratory and spiracles 5–9 are respiratory.Respiratory spiracles in both species are characterized by activity patterns of their motoneurones during respiratory tracheal ventilation: low frequency firing at irregular intervals during the respiratory pause and a higher frequency burst synchronous with the expiratory abdominal compression. Non-respiratory spiracles are characterized by complete inactivity of their opener motoneurones during respiratory tracheal ventilation. These motoneurones are activated by mechanical stimulation in both species, which simultaneously suppresses activity in respiratory opener motoneurones. In Blaberus discoidalis, there are no differences between activity patterns of respiratory and non-respiratory closer motoneurones. In Gromphadorhina portentosa, not only do respiratory and non-respiratory closer motoneurones have different activity patterns, but the activity pattern of respiratory closer motoneurones is different during respiratory and non-respiratory tracheal ventilation. The functional implications of these several spiracular motoneurone activity patterns are discussed.     

Monitoring of gas exchange cycles and ventilatory movements in the pine weevil Hylobius abietis: respiratory failures evoked by a botanical insecticide

The large pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae), is the most important insect pest of young coniferous plants. The implementation of new control methods requires not only a profound knowledge of the ecology and behaviour of the pest, but particularly of its physiology. Standard metabolic rate (SMR) and discontinuous gas exchange cycles (DGCs) were recorded in parallel with abdominal ventilation movements in adults of H. abietis using a differential electrolytic respirometer‐actograph. Quiescent weevils displayed DGCs of the constriction, flutter, and ventilation phases of the CFV type, while bursts of carbon dioxide were always accompanied by abdominal pumping movements, i.e., muscular ventilation in the closed subelytral cavity (SEC). In some beetles the C phase was absent and thus (C)FV cycles were recorded. In addition, at the beginning and often at the end of a burst, the SEC was rhythmically opened and closed by movements of the last abdominal segments. Continuous pumping movements and an absence of DGCs were signs of stress imposed by handling or by a new environment, even if the beetle was not moving. All individuals showed clear DGCs after recovering from handling and apparatus stress lasting 2–3 h. The results show that in the monitoring of DGCs, it is essential to determine whether they are of the constriction, flutter, and open phases (CFO), or the CFV subtype of the constriction, flutter, and burst (CFB) cycles. Use of our simple closed‐system respirometer enables non‐invasive simultaneous recording of SMR, oxygen uptake, DGCs, and active ventilation in H. abietis and other beetles. The topical application of adult H. abietis with sublethal doses of a botanical insecticide, NeemAzal T/S, caused essential respiratory failures: cyclic gas exchange was lost and irregular pumping movements appeared. In the treated beetles normal DGCs did not resume.     

The role of the spiracles in gas exchange during development of Samia cynthia (Lepidoptera, Saturniidae)

Spiracles and the tracheal system of insects allow effective delivery of respiratory gases. During development, holometabolous insects encounter large changes in the functional morphology of gas exchange structures. To investigate changes in respiratory patterns during development, CO₂-release was measured in larvae, pre-pupae and pupae of Samia cynthia (Lepidoptera, Saturniidae). Gas exchange patterns showed great variability. Caterpillars had high metabolic rates and released carbon dioxide continuously. Pre-pupae and pupae showed typical discontinuous gas exchange cycles (DGC) at reduced metabolic rates. Changes in gas exchange patterns can partly be explained with low metabolic rates during pupation. Sequential blocking of spiracles in pre-pupae and pupae reduced spiracle conductance with tracheal conductance remaining unaffected. Analysis of gas exchange patterns indicates that caterpillars and pre-pupae use more than 14 spiracles simultaneously while pupae only use 8 to 10 spiracles. Total conductance is not a simple multiple of single spiracles, but may be gradually adaptable to gas exchange demands. Surprisingly, moth pupae showed a DGC if all except one spiracle were blocked. The huge conductance of single spiracles is discussed as a pre-adaptation to high metabolic demands at the beginning and the end of the pupal as well as in the adult stage.     

Breathe softly, beetle: continuous gas exchange, water loss and the role of the subelytral space in the tenebrionid beetle, Eleodes obscura

Flightless, diurnal tenebrionid beetles are commonly found in deserts. They possess a curious morphological adaptation, the subelytral cavity (an air space beneath the fused elytra) the function of which is not completely understood. In the tenebrionid beetle Eleodes obscura, we measured abdominal movements within the subelytral cavity, and the activity of the pygidial cleft (which seals or unseals the subelytral cavity), simultaneously with total CO2 release rate and water loss rate. First, we found that E. obscura has the lowest cuticular permeability measured in flow-through respirometry in an insect (0.90 microg H2O cm(-2) Torr(-1) h(-1)). Second, it does not exhibit a discontinuous gas exchange cycle. Third, we describe the temporal coupling between gas exchange, water loss, subelytral space volume, and the capacity of the subelytral space to exchange gases with its surroundings as indicated by pygidial cleft state. Fourth, we suggest possible mechanisms that may reduce respiratory water loss rates in E. obscura. Finally, we suggest that E. obscura cannot exchange respiratory gases discontinuously because of a morphological constraint (small tracheal or spiracular conductance). This "conductance constraint hypothesis" may help to explain the otherwise puzzling phylogenetic patterns of continuous vs. discontinuous gas exchange observed in tracheate arthropods.     

Tracheal ultrastructure of protura (Insecta : Apterygota)

The tracheal systems of Sinentomon and Eosentomon (Apterygota : Protura) were examined in thin sections and compared with the tracheae of collembolan, Allacma. The tracheal system of Protura consists of spiracles and tracheae. The spiracle is a simple, concave cuticular cavity known as an atrium. A globular chamber is present between the atrium and trachea. The atrium of Eosentomon is decorated with ridges and has 2 small openings to tracheal recesses beside the central tracheal opening. The tracheae of Protura are characterized by a high frequency of taenidia and the absence of intima folds and intertaenidial spaces. The taenidia of Sinentomon have a rectangular section and those of Eosentomon are gable-shaped. The results also suggest that the tracheal recess of Eosentomon is a kind of stigmatic gland. The tracheal structure of Protura was compared with that of collembolans, insects, and other arthropods, and discussed in terms of phylogeny.     

Tradeoffs between metabolic rate and spiracular conductance in discontinuous gas exchange of Samia cynthia (Lepidoptera, Saturniidae)

The insect tracheal system is a unique respiratory system, designed for maximum oxygen delivery at high metabolic demands, e.g. during activity and at high ambient temperatures. Therefore, large safety margins are required for tracheal and spiracular conductance. Spiracles are the entry to the tracheal system and play an important role in controlling discontinuous gas exchange (DGC) between tracheal system and atmosphere in moth pupae. We investigated the effect of modulated metabolic rate (by changing ambient temperature) and modulated spiracular conductance (by blocking all except one spiracles) on gas exchange patterns in Samia pupae. Both, spiracle blocking and metabolic rates, affected respiratory behavior in Samia cynthia pupae. While animals showed discontinuous gas exchange cycles at lower temperatures with unblocked spiracles, the respiratory patterns were cyclic at higher temperatures, with partly blocked spiracles or a combination of these two factors. The threshold for the transition from a discontinuous (DGC) to a cyclic gas exchange (^cycGE) was significantly higher in animals with unblocked spiracles (18.7 nmol g⁻¹ min⁻¹ vs. 7.9 nmol g⁻¹ min⁻¹). These findings indicate an important influence of spiracle conductance on the DGC, which may occur mostly in insects showing high spiracular conductances and low metabolic rates.     

Tracheal system and biology of the Early Cretaceous <Emphasis Type="Italic">Saurophthirus longipes</Emphasis> Ponomarenko, 1976 (Insecta, ?Aphaniptera,Saurophthiroidea stat. nov.)

The tracheal system of Saurophthiridae is described based on female fossils of Saurophthirus longipes Ponomarenko, 1976. Three very wide tracheal trunks are found running dorsolaterally along each side of the body. The tracheal system is amphipneustic, with the large mesothoracic and very large 8th abdominal spiracles. The 9th and following segments are able to turn back to open posterior spiracles for breathing. Taken together, these features are characteristic of air breathing aquatic insects. This urges us to modify the former hypothesis about parasitism of Saurophthirus on pterosaur wing membrane. We suppose that Saurophthirus females had gonotrophic cycles: they imbibed blood enough for maturation of a large egg batch, then retreated to a water body as a safe place for digesting and egg maturation, and after oviposition climbed onto emergent plants and waited for pterosaurs patrolling over the water and looking for fish, to start a new cycle. The families Saurophthiridae, Pseudopulicidae, and Tarwiniidae are united in the superfamily Saurophthiroidea Ponomarenko, 1986, stat. nov.     

Postillumination burst of carbon dioxide in crassalacean Acid metabolism plants

Immediately following exposure to light, a postillumination burst of CO₂ has been detected in Crassulacean acid metabolism plants. A detailed study with pineapple (Ananas comosus) leaves indicates that the postillumination burst changes its amplitude and kinetics during the course of a day. In air, the postillumination burst in pineapple leaves generally is exhibited as two peaks. The postillumination burst is sensitive to atmospheric CO₂ and O₂ concentrations as well as to the light intensity under which plants are grown. We propose that the CO₂ released in the first postillumination burst peak is indicative of photorespiration since it is sensitive to either O₂ or CO₂ concentration while the second CO₂ evolution peak is likely due to decarboxylation of organic acids involved in Crassulacean acid metabolism.     

The respiratory basis of locomotion in Drosophila

The respiratory system of insects has evolved to satisfy the oxygen supply during rest and energetically demanding processes such as locomotion. Flapping flight in particular is considered a key trait in insect evolution and requires an increase in metabolic activity of 10-15-fold the resting metabolism. Two major trade-offs are associated with the extensive development of the tracheal system and the function of spiracles in insects: the risk of desiccation because body water may leave the tracheal system when spiracles open for gas exchange and the risk of toxic tracheal oxygen levels at low metabolic activity. In resting animals there is an ongoing debate on the function and evolution of spiracle opening behavior, focusing mainly on discontinuous gas exchange patterns. During locomotion, large insects typically satisfy the increased respiratory requirements by various forms of ventilation, whereas in small insects such as Drosophila diffusive processes are thought to be sufficient. Recent data, however, have shown that during flight even small insects employ ventilatory mechanisms, potentially helping to balance respiratory currents inside the tracheal system. This review broadly summarizes our current knowledge on breathing strategies and spiracle function in the genus Drosophila, highlighting the gas exchange strategies in resting, running and flying animals.     

Modulation of cyclic CO2 release in response to endogenous changes of metabolism during pupal development of Zophobas rugipes (Coleoptera: Tenebrionidae)

Understanding the mechanisms of gas exchange regulation in insects currently is a hot topic of insect physiology. Endogenous variation of metabolism during pupal development offers a great opportunity to study the regulation of respiratory patterns in insects. Here we show that metabolic rates during pupal development of the tenebrionid beetle Zophobas rugipes reveal a typical U-shaped curve and that, with the exception of 9-day-old pupae, the time between two bursts of CO₂ (interburst phase) was the only parameter of cyclic CO₂ gas exchange patterns that was adjusted to changing metabolic rates. The volume of CO₂ released in a burst was kept constant, suggesting a regulation for accumulation and release of a fixed amount of CO₂ throughout pupal development. We detected a variety of discontinuous and cyclic gas exchange patterns, which were not correlated with any periods of pupal development, suggesting a high among individual variability. An occasional occurrence of continuous CO₂ release patterns at low metabolic rates was very likely caused by single defective non-occluding spiracles.     

Estimation of Photorespiration Based on the Initial Rate of Postillumination CO(2) Release: I. A Nonsteady State Model for Measurement of CO(2) Exchange Transients

Although open systems have been used for the study of transients in leaf CO₂ exchange such as the postillumination burst, these systems frequently do not permit reliable estimates of transient rates due to their nonsteady state nature. A nonsteady state mathematical approach is described which predicts changes in CO₂ concentration in the leaf chamber and infrared gas analyzer measuring cell as a function of leaf CO₂ exchange rate in Nicotiana tabacum vars John Williams Broadleaf and Havana Seed. With the aid of a computer, a numerical formula simulates the mixing and dilution which occurs as CO₂ passes through the finite volume of the measuring cell of the analyzer. The method is presented with special relevance to photorespiration as manifested by the postillumination burst of CO₂. The latter is suggested to decline with the first order kinetics following darkening of a C₃ leaf. This approach provides a basis for reliable estimation of the initial and, hence, maximal rate of CO₂ evolution during the postillumination burst under a variety of environmental conditions.     

普通齿蛉幼虫的呼吸系统及呼吸行为

研究了普通齿蛉Neoneuromus ignobilis Navás幼虫的呼吸系统及其呼吸行为。结果表明:普通齿蛉幼虫为全气门式(10对气门)呼吸系统,前中胸、中后胸之间、腹部8节各有1对气门,腹部8节各有气管鳃1对,前6对细短,管状,有较短绒毛,后2对气管鳃较粗长,呈羽毛状。腹部1～7节各有1对毛簇,第8腹节无毛簇。侧纵干气管较粗,4束,自前胸前缘部分成左右2组,每组两根侧纵干气管,向胸腹部延伸,二级气管分别伸达各个气门和毛簇,腹部每节由毛簇处的二级气管分支而来的三级气管相连或延伸至消化道等处。气管鳃中无气管。有毛簇呼吸、气门呼吸和体壁呼吸3种呼吸方式,在水中以毛簇呼吸为主,在陆上进行气门呼吸和体壁呼吸。     

Co-ordinating interneurones of the locust which convey two patterns of motor commands: their connexions with ventilatory motoneurones.

1. The interneurones which make widespread connexions with flight motoneurones also synapse upon ventilatory motoneurones so that in all 50 motoneurones receive synapses. They influence three aspects of ventilation; (a) the closing and opening movements of the thoracic spiracles, (b) some aspects of abdominal pumping movements and (c) the recruitment of some motoneurones controlling head pumping. 2. The two closer motoneurones of a particular thoracic spiracle receive the same excitatory synaptic inputs (EPSPs) during expiration. The EPSPs match those in appropriate flight motoneurones. 3. The closer motoneurones of each thoracic spiracle whose somata are in the pro-, meso- or metathoracic ganglia all receive the same excitatory synaptic inputs. These inputs are an adequate explanation of the pattern of spikes in the closer motoneurones. Both the slow ventilatory and fast rhythms of synaptic potentials are expressed as spikes; the slow as the overall expiratory burst of spikes and the fast as the groups of spikes within that burst. This establishes a ventilatory function for the interneurones. All thoracic closer motoneurones therefore receive the same excitatory commands which will tend to synchronize the movements of each spiracle. 4. Spiracular opener motoneurones are inhibited during expiration, their IPSPs matching the EPSPs in flight or closer motoneurones. Therefore the interneurones have reciprocal effects on the antagonistic motoneurones of the spiracles. 5. The interneurones synapse upon some motoneurones which control the pumping movements of the abdomen and which have their somata in the metathoracic or first unfused abdominal ganglion. Motoneurones in four separate ganglia therefore receive inputs from these interneurones. 6. The interneurones also synapse upon motoneurones which control an auxiliary form of ventilation, head pumping.     

Respiratory system of the primitive moth Micropterix calthella (Linnaeus) (Lepidoptera : Micropterigidae)

The 1st thoracic spiracular atrium is closed by anterior and posterior muscle fibres extending between its dorsal and ventral wall. The 2nd thoracic spiracle has only a single (anterior) closing lip, movable by a muscle inserting on the wall below the spiracular aperture; this configuration may be a lepidopteran ground-plan autapomorphy. There are functional spiracles on abdominal segments I – VII, each with a closing “bow” and “lever”. There are intrinsic occlusor muscles in all abdominal spiracles and the 1st spiracle has an extrinsic (ventral) dilator. Dorsal dilator muscles or ligaments are absent. A dorsal and a ventral tracheal trunk extend from the 1st thoracic spiracle into the head; the latter supplies the mouthparts and the antenna; there is no connection between the dorsal and ventral cephalic trunk systems. There is a single series of lateral connectives between the spiracles of each side. There is a ventral tracheal commissure in both pterothoracic segments, but none in the prothorax. In each pterothoracic segment an anterior and a posterior tracheal arch give off branches to the wing and anastomose with each other on their downwards course into the leg. Wing tracheation is greatly reduced. The anterior and posterior tracheae of each wing are independent of each other. There is a dorsal commissure in abdominal segment VIII; ventral abdominal commissures are lacking in Micropterix, although present in other micropterigid genera. The terminalia are partly supplied from tracheae arising in segment VII. Air sacs occur in the tibiae only. Phylogenetic aspects of holometabolan tracheation patterns are discussed.     

Effects of Neem EC on gas exchange, tracheal ventilation, and water loss in diapausing pupae of Pieris brassicae

Effects of Neem EC (The Indian Neem Tree Company^TM, 1% azadirachtin) on gas exchange cycles, tracheal ventilation, and water loss in diapausing pupae of the large white butterfly, Pieris brassicae L. (Lepidoptera: Pieridae), were studied using a constant volume respirometer combined with an infrared probe actograph. The non‐treated pupae displayed discontinuous gas exchange cycles (DGC) with a trend coinciding with the bursts of carbon dioxide (CO₂) release, active tracheal ventilation, and the heartbeat periods. Two independent forms of tracheal ventilation were observed, relatively vigorous abdominal shaking movements and weak abdominal pulsations. The ability to respond to mechanical excitation with abdominal movements was entirely lost on the 2nd day after treatments with Neem EC, and also a reduced tendency to use a DGC was observed. During 2–3 days after treatments, the DGCs and gas exchange microcycles were entirely lost, as was active ventilation. Before treatments, body mass loss, that is, water loss, was 0.6–0.9 mg g^?1 day^?1. After the treatments, water loss increased to 3–5 mg g^?1 day^?1. The pupae remained alive for 10–15 days after the treatments and died after having lost about 50% of their initial body mass. The absence of heartbeats measured during at least 4–5 h was the main criterion for ascertaining death of pupae. The results suggested that respiratory failures, that is, the loss of cyclic gas exchange, evoked by Neem EC were the primary cause of lethal desiccation. Thus, the hypothesis that the cyclic gas exchange is an adaptation for restricting water losses in insects was supported.     

Spiracular closing mechanisms in the firebrat, Thermobia domestica (packard) (Thysanura)

Mechanisms for regulating the degree of opening of its spiracles are present in Thermobia. That of the mesothoracic spiracle is of the external type with a flap-like hood guarding the spiracular aperture. Contraction of muscles open the spiracle by raising the hood. Closure is brought about by muscular relaxation and elastic cuticular recoil. Opening is either partial, with small-scale oscillatory movements ('fluttering'), or complete ('wide-opening'). Wide-opening follows bouts of muscular activity. Carbon dioxide anaesthesia relaxes the opener muscles causing the spiracles to close by elastic recoil. This explains continued low tracheal water loss during anaesthesia, and also in death. The control mechanisms of the metathoracic and 8 pairs of abdominal spiracles are of the internal type, with a crypt-like atrium leading into the slit-like neck region of the spiracular pit, one side of which has an elastic cuticular rod running along it. Muscles inserted on the opposite side widen the aperture. As with the mesothoracic spiracle, closure is brought about by muscular relaxation and elastic cuticular recoil.     

Respiratory significance of the thoracic and abdominal morphology of Belostoma and Ranatra (insecta,heteroptera)

Summary Both Belostoma and Ranatra possess I–II, subepimeral, thoracic subalar, and abdominal subalar air stores. In Belostoma, unlike Ranatra, the subepimeral air store is greatly enlarged, the abdominal subalar store is partially exposed to the water, and a fully exposed ventral abdominal air store is also present. All the air stores of Ranatra are normally concealed.The mesothoracic and metathoracic spiracles, which open onto the I–II and subepimeral air stores respectively, are of limited permeability. They appear to have less respiratory importance than the large and highly permeable first abdominal spiracles, which lie in the subalar air space and can probably exhale and inhale large amounts of air. The large eighth abdominal spiracles, which lie at the base of the siphon or retractile organ, can also inhale or exhale much air in Ranatra but appear to be mainly exhalant in Belostoma. The smaller second through seventh abdominal spiracles structurally resemble the eighth ones in Belostoma and open onto the ventral abdominal air store. In Ranatra they appear to have no significant respiratory function.Both genera obtain atmospheric air and give off exhaled air by means of the posterior retractile organ or siphon. The two types of air appear to follow different pathways in the two genera. In Ranatra atmospheric air appears to enter the tracheal system mainly or entirely through the eighth abdominal spiracles and then passes through the first abdominal spiracles into the subalar space. Exhaled air follows the reverse pathway. In Belostoma, however, atmospheric air probably enters the tracheae mainly through the first abdominal spiracles; it is conveyed to these spiracles from the retractile organ through the subalar space or, more indirectly, through the ventral abdominal air store. Air exhaled through the first abdominal spiracles follows the reverse route; the eighth abdominal spiracles can also exhale directly into the base of the retractile organ.During underwater respiration the abdominal portion of the subalar air store appears to be the main reservoir for oxygen. The subalar oxygen is initially atmospheric, and is supplemented, during submersion, by other sources of oxygen. Belostoma may use its exposed ventral abdominal air store, and its partially exposed abdominal subalar one, as physical gills; both these stores communicate with the inhalant first abdominal spiracles. Ranatra, none of whose air stores are normally exposed, appears, to be less capable of utilizing dissolved oxygen, but the considerable amount of atmospheric oxygen in the elongated siphon may be inhaled, during submersion, through the eighth abdominal spiracles.In both genera the thoracic air stores appear to be of less respiratory importance than the abdominal ones. They do not appear capable of obtaining large amounts of oxygen, and the thoracic spiracles are relatively impermeable. All the air stores, however, serve to protect the spiracles against the entry of water, and also contribute to the body's hydrostatic balance. It is also possible that some of the air stores play a role in pressure reception.The literature indicates much intergeneric variation in the respiration of Belostomatidae and Nepidae. In the Belostomatidae there is considerable variation in the extent of the ventral abdominal air store and in the roles of the subalar air store and the spiracles. The Nepidae show differences in their ability to utilize dissolved oxygen and in the extent of the subepimeral air store.     

The probable significance of tracheal tufts in the 8th abdominal segment of Heliothis virescens (F.) on the development of its parasitoid, Toxoneuron nigriceps (Viereck)

The 8th abdominal segment of Heliothis virescens (Fabricius) larvae contains aerating trachea and tracheole tufts that end in the hemocoel of the 8th segment, unlike the tracheae that invade tissues in other segments. These tracheal tufts from the 8th abdominal segment extend to the tokus region, which along with the telson cavity is known to act as a “lung” for hemocytes in Calpodes ethlius and a few other lepidopteran larvae. The goal of this research was to study the effects of these tracheal tufts in the 8th abdominal segment on parasitoid development inside the host larvae, H. virescens. The first objective was to determine if the eggs of the parasitoid, Toxoneuron nigriceps, are predominantly located among the tracheal tufts of the 8th abdominal segment compared to other body cavity regions irrespective of their oviposition site or the position of the host larvae. The results showed that several hours after oviposition most of the eggs are found in the 8th abdominal segment irrespective of the oviposition site or the position of the host larvae. The second objective was to study the effect of varying oxygen concentrations in vitro on various developmental stages of the egg. The results showed that decreasing oxygen concentrations adversely affects the parasitoid egg development in vitro. A third objective was to determine the oxygen concentration in 8th abdominal segment of the host larvae and compare it to other regions of the body using an oxygen sensor placed in vivo. The results suggested relatively high concentration of oxygen in the 8th abdominal segment compared to other regions of the host, thus supporting our hypothesis that the increased oxygen level in the 8th abdominal segment is important to the development of the parasitoid eggs.