Spiracular Opening Research Articles

Insect acid-base physiology.

Acid-base status influences many aspects of insect biology, including insect distributions in aquatic systems, insect-plant and insect-pathogen interactions, membrane transport phenomena, and the mode of action of pesticides. Acid-base status in the hemolymph and gut lumen of insects is generally well regulated but varies somewhat within individuals owing to effects of temperature, activity, discontinuous ventilation, and diet. The pH of the midgut lumen varies with the phylogeny and feeding ecology. Insect fluids have buffer values similar to those of vertebrates. The respiratory system participates in acid-base homeostasis primarily by regulating the internal carbon dioxide (partial) pressure via changes in spiracular opening and convective ventilation. The epithelia of the renal system and gut participate in hemolymph acid-base regulation by varying acid-base transport in response to organismal acid-base status. Evidence to date suggests that the dominant mechanisms for control of renal acid-base excretion involve hormonal regulation of H+-V-ATPase activity.

Scanning electron microscopy of the second-instar larva of Gasterophilus nasalis.

The second-instar larva of the bot fly Gasterophilus nasalis (L.) (Diptera: Gasterophilidae) is described for the first time, based on scanning electron microscope (SEM) studies. On the pseudocephalum the larva bears an antenomaxillary sensory complex formed by the antenna (coeloconic sensilla) and the maxillary palp with a set of six coeloconic sensilla and four basiconica sensilla. The oral opening is latero-posteriorly limited by small spines, and exhibits strongly ornamented maxillae and mandibles. The thoracic and abdominal segments are circled by two bands, each with two rows (except the last segment that has one row) of backwardly pointed spines, and have cuticular depressions. Trichoid and campaniform sensilla surround the larval segments. The anterior spiracular opening is a small aperture. The terminal end of the eighth abdominal segment shows a spiracular cavity, lateral tubercles, eight basiconic and two trichoid sensilla. Each spiracular plate has two slightly curved slits, each with a serrated rima. There is a probable ecdysial scar. The findings of this ultrastructural study are compared with those other of larval flies.

Comparative morphology of the spiracles of the Papilionidae, Sphingidae, and Saturniidae (Insecta: Lepidoptera)

The morphology, ultrastructure, and innervation of the spiracles of the instars and adults of representatives of three lepidopteran families were examined: Ornithoptera priamus poseidon and Pachliopta aristolochiae (Papilionidae), Attacus atlas (Saturniidae), and Acherontia atropos (Sphingidae). Peritreme and atrium show stage- and family-specific structures for protecting the internal valve apparatus. The gross morphology of the cuticular valve mechanism is uniform within the three families, consisting of a rigid bow and a movable bar with a lever. In adult Papilionidae, all cuticular parts (bow, bar and lever) of the valve are innervated by multipolar dendrites. Internal or external cuticular chemo- or hygroreceptors, which could participate in the regulation of respiration, could not be detected in any stage. The closing muscle inserts between the tip of the lever and the base of the bar, and is innervated only by motor neurons. The elasticity of the cuticular system and an opener are the antagonists to the closing muscle. The spiracular opener of the adult Papilionidae and of all instars of the moths is an elastic ligament. The opener of the larval and pupal spiracles of the Papilionidae, however, is a single thickened muscle fiber surrounded by an elastic sheath of connective tissue. As it contains motor and multipolar sensory neurons, we assume that it may function as a stretch receptor for controlling the spiracular opening state.

Roles of aorta, ostia and tracheae in heartbeat and respiratory gas exchange in pupae of Troides rhadamantus Staudinger 1888 and Ornithoptera priamus L. 1758 (Lepidoptera, Papilionidae)

In non-diapausing pupae of the two birdwing butterfly species Troides rhadamantus and Ornithoptera priamus (Lepidoptera, Papilionidae) heart activity and CO 2 release rates were measured simultaneously within the initial half of pupal development. Heartbeat patterns in these pupae consist of three different types of activity: Continuous forward-pulse periods of different duration with a frequency range of about 0.25–0.52 s −1, continuous backward-pulse periods with lower frequencies (0.15–0.29 s −1) and intermittent backward-pulse periods when short series of three to 10 single heartbeats at frequencies of 0.12–0.35 s −1 alternated with heart pauses of 2–10 min. CO 2 release was discontinuous (CFO-type) from about four to 12 days after pupation in Troides rhadamantus and from about four to 18 days in Ornithoptera priamus. Mean CO 2 release rates were very low in both species (10–30 nmol g −1 min −1). After this period, heart pauses occurred more frequently, probably indicating the onset of metamorphosis and the beginning partial histolysis of the heart. Infrared-optical and thermometrical measurements of heartbeat indicated that haemolymph transport within the dorsal vessel in forward direction is more effective than in backward direction. This is deduced from the higher heartbeat frequency and heartbeat amplitude of the forward pulsations. Results from ultrasonic doppler velocimetry suggest that haemolymph flow velocity is highest during the relatively long diastasis of 2–3 s (30–40 mm s −1), while minimum particle speed (about 20 mm s −1) is at the end of systole and the beginning of diastole. This would mean that haemolymph velocity is highest between two consecutive peristaltic waves. In contrast to the haemolymph velocity, the speed of the peristaltic wave measured with the infrared transmission technique was lower (about 8.4–22 mm s −1 in Troides, 10–23 mm s −1 in Ornithoptera) and remained constant during forward pulse periods. During backward beating the speed was lower (8–20 mm s −1 in Troides, 9–17 mm s −1 in Ornithoptera) and decreased during backward pulse periods. During day two to seven in Troides and day three to nine in Ornithoptera, spiracular opening periods coincided with changes in heartbeat direction from backward to forward pulsations. A possible influence is the more efficient convective haemolymph mixing in the haemocoel during forward heartbeat. The mixing allows to bring the haemolymph in close contact with the tracheal system where the discharge of CO 2 takes place. Heartbeat may therefore serve for shortening the diffusion pathways for a rapid transition into the tracheal system during the open period of the spiracles.

Strategies for hearing in noise: peripheral control over auditory sensitivity in the bushcricket sciarasaga quadrata (Austrosaginae: tettigoniidae)

The carrier frequency of the call of the Australian bushcricket Sciarasaga quadrata is unusually low for tettigoniids at 5 kHz. The sound transmission measured in the habitat of the insect reflects the advantages of producing low- rather than high-frequency signals; attenuation is explained almost entirely by the spherical spreading of sound. The natural vibration frequency of the wings is controlled by size and stiffness. The small tegmina are unusually fleshy, with an order-of-magnitude higher water content than in comparable sagine species. Reduced stiffness allows the insect to call at low carrier frequencies, albeit at lower intensity levels (60 dB SPL at 1 m), than bushcrickets of comparable size (80-90 dB SPL). The responses of the tympanic nerve and a first-order interneurone (omega neurone) in the afferent auditory pathway showed that the hearing system is most sensitive to frequencies of 15-20 kHz, an effective mismatch to the conspecific call resulting in a reduced sensitivity of approximately 20 dB at the carrier frequency of the call. S. quadrata can occlude its spiracular opening, which increases the sensitivity of the ear to lower frequencies. Under such conditions, the best frequency of the ear matched that of the carrier frequency of the call. We measured the activity of auditory neurones in the field, noting the ability of the open and partially closed ear to filter out potentially masking calls of congenerics. At the same time, the directionality of the system was only slightly reduced in the closed relative to the open spiracle status. We discuss the evolutionary advantages of an insect both calling with a low carrier frequency and having the ability to close down the tracheal system to avoid the effects of masking. In addition, we consider the advantages of such a signalling system in avoiding the most significant predator of the male, the ormine fly Homotrixa alleni. <P>

Morphology of the second- and third-instar larvae of Dermatobia hominis by scanning electron microscopy.

Larvae of Dermatobia hominis 10-27 days old were collected from experimentally infected rats and their morphology was studied by scanning electron microscopy. The moult from the second to third instar occurs at 18 days, with emergence from the host at 30 days post-infection. The second-instar larvae bear on the pseudocephalon, antennae (coeloconic sensilla), and coeloconic and basicoconic sensilla on the maxillary sensory complex. The thoracic segments bear small backwardly-directed spines anteriorly and ventral trichoid and campaniform sensilla. The first four abdominal segments have small and large backwardly-directed spines that are absent on segments five and six. The seventh and eighth abdominal segments have medium-sized forwardly-directed spines. Abdominal segments are encircled by campaniform sensilla. The terminal end of the eighth abdominal segment bears the anus, prominent anal lobes and two spiracular openings on each spiracular plate. Spiracular plates show a radial sun ray pattern. The rear abdomen also bears an ecdysal aperture, several pores and eight coeloconic sensilla. Although there are slight morphological differences, the spines (predominantly flat and thorn-like) and sensilla (campaniform and coeloconic) of the third-instar larvae show a similar arrangement to that of second-instar larvae. Thoracic trichoid sensilla are not seen in third-instar larvae. A perispiracular gland aperture is situated above each posterior spiracular opening. These morphological features are compared with those of other cuterebrid larvae.

Ventilatory Mechanism and Control in Grasshoppers

Synopsis. Grasshoppers exhibit a diversity of ventilatory patterns depending on activity status. For each pattern, the mechanism and control of gas exchange is analyzed in terms of a two-step model, consisting of tracheolar and trans-spiracular steps in series. During the intermittent gas exchange that characterizes the most quiescent grasshoppers, spiracles open and close in response to changing carbon dioxide, and trans-spiracular resistance controls gas exchange. In resting but alert grasshoppers, abdominal pumping occurs, and gas exchange is controlled equally by tracheolar and trans-spiracular resistances; tracheal oxygen and carbon dioxide are regulated by variation in abdominal pumping and spiracular opening. During hopping, abdominal pumping does not occur, and bulk gas flow is driven by cuticular deformations associated with locomotion. Increased cellular oxygen consumption depends on use of internal oxygen stores and increased partial pressure gradients. After hopping ceases, abdominal pumping increases dramatically and restores tracheal gas composition; however, the rise in abdominal pumping after hopping is not affected by tracheal gas levels. During flight, bulk flow to the flight muscles is driven by tidal thoracic auto-ventilation, while the remainder of the body is ventilated by abdominal pumping. During both hop? ping and flight, the greatest resistances to gas transport exist in the tracheo? lar rather than the trans-spiracular step.

Acid-base status and spiracular control during discontinuous ventilation in grasshoppers

Many insects ventilate discontinuously when quiescent, exhibiting prolonged periods during which little or no gas exchange occurs. We investigated the consequences of discontinuous ventilation (DV) on haemolymph acid&shy;base status and tested whether spiracular opening during DV is due to changes in internal gas tensions in the western lubber grasshopper Taeniopoda eques. At 15 &deg;C, resting T. eques exhibited interburst periods of about 40 min. During the interburst period, haemolymph PCO2 rose from 1.8 to 2.26 kPa, with minimal acidification of haemolymph. Animals in atmospheres in which PCO2 was 2 kPa or below continued to exhibit DV, while atmospheres in which PCO2 was 2.9 kPa or above caused cessation of DV. These data indicate that accumulation of internal CO2 to threshold levels between 2 and 2.9 kPa induces spiracular opening in grasshoppers. In contrast to the situation in lepidopteran pupae, variation in atmospheric PO2 had no effect on interburst duration. Relative to lepidopteran pupae, the internal PCO2 of grasshoppers during DV is threefold lower, the PCO2 required for triggering spiracular opening is also threefold lower, and the open phase spiracular conductance is at least tenfold higher, demonstrating that considerable diversity exists in these aspects of insect respiratory physiology.

Ventilation chez les adultes d’&lt;em&gt;Amblyomma hebraeum&lt;/em&gt; et &lt;em&gt;A. marmoreum&lt;/em&gt; (Acarina, Ixodidae), vecteurs de la cowdriose en Afrique australe

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.

Discovery of the earliest-known tetrapod stapes.

The evolution of the middle ear is central to the discussion of how the first tetrapods adapted to life on land as well as their phylogeny. Here I report the discovery of the stapes of Acanthostega gunnari, from the Upper Devonian of east Greenland. This is the earliest tetrapod stapes so far described, and it throws new light on both these aspects of early tetrapod biology. It has been assumed that the common inheritance of all early tetrapods was a light, rod-like stapes associated with a temporal notch in the otic region that was thought to have supported a tympanum, or eardrum. The stapes would have conducted vibrations from the tympanum to the otic capsule. By contrast, the stapes of Acanthostega was stout with a broad distal ramus associated with the temporal notch. I suggest that the temporal notch of Acanthostega and other early tetrapods supported a spiracular opening rather than a tympanum, and that the stapes controlled palatal and spiracular movements in ventilation.

Scanning electron microscopy of the posterior spiracles of cattle grubs Hypoderma bovis and Hypoderma lineatum

Posterior spiracles of newly hatched first instar larvae of Hypoderma bovis (L.) and H. lineatum (DeVill.) consist of two pairs of spiracular openings. Each pair is surrounded by a rima bearing three spines. Posterior spiracles of second instar larvae are composed of a pair of medial ecdysial scars bounded laterally by spiracular plates. H. bovis spiracular plates have twenty-nine to forty openings, each surrounded by a slightly raised rima. H. lineatum spiracular plates have eighteen to twenty-five openings. Spiracular openings lead to posterior felt chambers which are connected to a common anterior felt chamber filled with a meshlike network. In third instar H. bovis each medial ecdysial scar is surrounded by a strongly concave spiracular plate. Spiracular openings are surrounded by slightly raised rima. Most rimae bear a spine. Spiracular plates of H. lineatum are flat and rimae are without spines. Each spiracular opening leads to a posterior felt chamber, several of which are confluent with a larger anterior felt chamber. Anterior felt chambers open into the dorsal longitudinal tracheal trunk. Felt chambers in third instar larvae are also filled with a complex mesh.

Modified Dissection Technique for Diagnosis of Tracheal Mites (Acari: Tarsonemidae) in Honey Bees (Hymenoptera: Apidae)

A technique is described for rapid dissection of adult honey bees, Apis mellifera L., to facilitate diagnosis of honey bee tracheal mites, Acarapis woodi Rennie, in the large tracheae connected to the first pair of thoracic spiracles. After dissection, tracheae are visible along their entire length. Light infestations or single-mite infestations near the spiracular opening are detectable. A dissecting microscope (25–50×), an adequate light source, and simple dissection tools are required.

On the respiration of Torpedo marmorata.

1. The oxygen consumption of resting Torpedo marmorata was measured using three different methods. The results indicate that this species has a much lower oxygen consumption than other elasmobranchs of comparable size. 2. The gills are ventilated by a mechanism similar to that of other rays, but a relatively small spiracular opening seems to be associated with a more important role of the oro-branchial pump. During hypoxia there is a marked increase in both frequency and amplitude of the ventilatory movements. 3. The frequency of the heart beat is low and shows little change during hypoxia, except under extreme conditions when bradycardia occurs. 4. In some individuals, coupling between cardiac and ventilatory pumps is relatively low but seems to increase at lower ventilatory frequencies and when the ratio between the ventilatory and cardiac frequencies is a whole number. 5. Extreme hypoxia can be withstood for many hours but eventually the ventilatory rhythm ceases; it does not recommence immediately following a rise in ambient oxygen tension. 6. The blood has a low oxygen-carrying capacity and a high affinity. 7. The surface area of the gills is smaller than that of other species that have been investigated, but the quantity of oxygen transferred/unit surface area is similar to that known for other species. 8. It is concluded that Torpedo is a sluggish fish adapted to conditions of low oxygen, but the conditions under which this occurs remain to be determined.

The physiology of the tettigoniid ear. I. The implications of the anatomy of the ear to its function in sound reception.

ABSTRACT The acoustic opening of the large, double prothoracic spiracle gives rise to a vesicula and a trachea which descends into the leg and divides to form the anterior and posterior tympanal air spaces, their apposed walls forming the secondary tympanal membrane. This trachea is independent of the respiratory system. The trachea is exponential or catenoidal in form in the Tettigoniids investigated, and the physics of horns is discussed in relation to the tracheal system. Bilateral recordings from the tympanal nerves have shown that blocking the spiracular opening eliminates the response to a sound signal at an intensity of 45 dB. Unilateral recordings during the blocking and reopening of both the spiracle and the tympanal slits has shown that at a sound intensity of 47·5 dB a response is obtained from the tympanal organ only when the sound is directed at an open spiracle; blocking the spiracle eliminates the response. Threshold curves for the ‘spiracle’ and for the ‘tympanal slits’ show a sensitivity difference of between 2 dB and 25 dB, the difference varying with frequency. The implications of this finding are discussed.

Effect of carbon dioxide gas on respiration of the confused flour beetle.

Concentrations of CO2 gas in the immediate surroundings play an important role in insect respiration by directing the spiracular openings. In fleas, Xenopsylla spp., the addition of 1% CO2 to outside air prolonged the spiracular opening period ca. 50%, and the addition of 2% caused the permanent opening of spiracles (Wigglesworth 1965). Similarly at this laboratory, while working with the effectiveness of different fumigants, we noticed that high CO2 concentration in surrounding atmospheres increased the fumigant toxicity, probably by interfering with normal respiratory behavior and physiology of insects (AliNiazee and Lindgren 1969). Preliminary studies were conducted to determine the rate of respiration of the adult confused flour beetle, Tribolium confusum Jacquelin du Val, in high CO2 atmospheres by measuring their CO2 output in small glass containers.

Influence of Age and Water Balance on Spiracular Behavior in Aedes Mosquitoes1

In female Aedes triscriatus (Say) (Diptera: Culicidae), duration of spiracular opening in air declined with sample age; in response to 0.5% CO2, both amplitude and duration of opening declined. There was no relationship of frequency of spiracular opening to age. Aspects of feeding behavior were observed and related to spiracular behavior in A. triseriatus and A. acgypti (L.). In the former species there was a diurnal weight loss; in both species inclusion of 0.2M KC1 in 0.3M sucrose solution led to a reduction in the amount of fluid imbibed. Spiracular opening became conservative in A. triseriatus , and to a lesser extent in A. acgypti when KC1 was included in the diet. A. acgypti engorged more than A. triseriatus and showed looser spiracular control. The course of starvation was more rapid in A. triseriatus than in A. acgypti ; the rate of water loss in the former was 4 times that in the latter. Each species showed increasingly conservative spiracular behavior as starvation proceeded.

Behavior of Thoracic Spiracles of Aedes Mosquitoes1 in Controlled Relative Humidities

Observations were made on the behavior of the thoracic spiracles of A. triseriatus (Say) and A. aegypti (L.) in high (90±5%) and low (<5%) relative humidities. Following a 5-minute exposure to low relative humidity, spiracular responses to 0.5% carbon dioxide were reduced in both species while only A. triseriatus showed attenuated spiracular behavior after a 2-minute exposure. Conservative spiracular opening was observed in both unfed and fed mosquitoes. It is postulated that the spiracular response to low relative humidity is a sensory one.

Spiracular esponses of Aedes mosquitoes to carbon dioxide and oxygen.

Observations were made on the responses of the thoracic spiracles of adult Aedes aegypti (L.), and adult A. triseriatus (Say) to a constant CO2 pressure in serial concentrations of O2 in N2 and to the O2 in N2 series alone. Less than atmospheric pressures of O2 caused an increase in the frequency and duration of spiracular opening. Higher than atmospheric O2 tensions had no effect on frequency of spiracular opening, but reduced the duration of opening. Carbon dioxide effected full spiracular opening in proportion to the O2 concentration. The duration of spiracular opening, regardless of amplitude, was also proportional to the ratio of CO2 to O2. Responses of Aedes spiracles to hypoxia and CO2 decreased with increasing duration of exposure.

Observations on spiracular behavior in Aedes mosquitoes.

Abstract : An apparatus was constructed to allow simultaneous observation of the thoracic spiracles of mosquitoes and to permit recording of the behavior observed. A microenvironment of controlled composition and relative humidity was provided. In Aedes aegypti and triseriatus at rest in air the thoracic spiracles constantly open and close synchronously, although the degree of opening is minimal. Stationary flight, carbon dioxide, or hypoxia cause much more extensive synchronized opening. It was suggested that the thoracic compressions and extensions of the head noted in flight or hypoxia are possible ventilatory mechanisms. These were unrelated to the frequency of spiracular opening and closing. Decapitation eliminated spontaneous locomotor activity and this resulted in more conservative spiracular behavior.

Spiracles of Adult Scarabaeoidea (Coleoptera) and Their Phylogenetic Significance. II. Thoracic Spiracles and Adjacent Sclerites1

The concealed mesothoracic spiracles of adult Scarabaeoidea have the same types of immobile filter apparatusas abdominal spiracles but usually differ in having amedial extension of the peritreme and have a different type of closing device. Associated with the mesothoracic spiracles are 1 or more setiferous intersegmentalia. Meta thoracic spiracles are simple in structure, have movablelips, and are unlike either mesothoracic or abdominal spiracles. Evolutionary trends found in mesothoracic spiracles are the development of a porous or solid filter apparatus from separate atrial spines, a reduction in the size of the spiracular opening, and a reduction in the number of intersegmentalia from several on each side to a median, setiferous sclerite. Many of the structures found in both mesothoracic spiracles and intersegmentalia appear to have taxonomic value. The degree of specialization found in both mesothoracic and abdominal spiracles and in adjacent structures is summarized. Pleocoma and the Lucanidae are the least specialized Scarabaeoidea; other less specialized groups are Passalidae, Troginae, Geotrupinae, Taurocerastinae, Oncerinae (Oncerus), Acoma, Podolasia , Glaphyrinae, Acanthocerinae, Ochodaeinae, and Allidostominae. Melolonthinae, Dynastinae, Rutelinae, and Cetoniinae are the most specialized groups.