Fluid movements during water-vapour absorption by the desert burrowing cockroach, Arenivaga investigata

The desert cockroach supplements its water intake by condensing atmospheric water onto the surface of protruded hypopharyngeal bladders. An associated pair of structures, the frontal bodies, produce a fluid which is conveyed to the bladder surface and added to by condensation. Reduced water activities on the bladder surface are maintained apparently by continuous removal of frontal-body fluid and condensate. This removal was demonstrated through application of nl quantities of fluorescent and radioactive tracer solutions to the bladder surface. Cuticular hairs are arranged on the bladder so as to divide it into a small (< 60 pl) suprasurface compartment and a large (32 nl) subsurface compartment. Rapid disappearance of fluorescent tracer from the bladder surface indicated movement of fluid from the suprasurface to the subsurface compartment. Radioactive tracer solutions were removed from the bladder, traversed the posterior hypopharynx, and accumulated in the oesophagus and crop. It is suggested that condensed fluid is conveyed to the crop in the same way. Tracer solutions were restricted to cuticular surfaces of the bladders, posterior hypopharynx, oesophagus and crop; other mouthparts are not involved in fluid movements. Movement of fluid into the subsurface compartment, and the small proportion of tracer solution which could be recovered from the bladder by Millipore filters with a pore size of 0.1 μm suggested the maintenance of considerable surface tensions on the bladder surface. Rapid removal of condensed fluid from the suprasurface compartment, where fluid is exposed to the atmosphere, suggests that the absorption mechanism is not dependent upon the properties of a hygroscopic solution. Over 99% of such a solution would be in the subsurface compartment, not exposed to the atmosphere, and would therefore be unavailable for the reduction of water activity.     

Anatomy of equilibrium receptors and cerci of the burrowing desert cockroach Arenivaga (Insecta,Blattodea)

Summary The anatomy of the cerci of a burrowing desert cockroach, Arenivaga sp., with particular emphasis on equilibrium receptors was studied by light and scanning electron microscopy. Each cercus has two parallel rows of pendulous equilibrium receptors called tricholiths; the rows are parallel to the long axis of the cercus. The cerci and rows of tricholiths are orthogonally positioned with respect to the long axis of the insect at the posterior end of the abdomen and rotated laterally by about 25° from the horizontal plane. Tricholiths of each row are inserted in their sockets toward the midline of the cercus and their elliptical attachment to the gasket is parallel to the long axis of the cercus. The combination of these anatomical features constrains tricholith movements to 90° from the long axis of each cercus and accounts for the physiological findings that (1) interneurons receiving afference from tricholiths are maximally sensitive to displacements of the insect at 45°, 135°, 225°, and 315°, and (2) interneurons receiving input from the lateral rows respond to smaller displacements than those driven by medial rows (Walthall and Hartman 1981). First instar cockroaches have only one tricholith on each cercus. Subsequent molts result in the addition of tricholiths, usually paired. After six molts, the adult female bears six pairs; the adult male seven pairs of tricholiths. The additional afference is presumably required to drive the increasingly larger interneurons.     

Vitellogenic arrest in the cockroach, Blatta orientalis

Starvation stimulated vitellogenic arrest occurs in the cockroach Blatta orientalis after 5 days. This is characterized by cessation of yolk uptake and oöcyte growth.After 5 days of starvation, protein and RNA synthesis decrease, but some macromolecular synthesis continues during the entire starvation period. No oöcyte resorption occurs for up to 15 days of starvation. In contrast to starvation, injection of actinomycin-D results in resorption within 8 hr. The results suggest that B. orientalis copes with starvation by maintaining arrested oöcytes as an alternative to immediate resorption.     

Neuroendocrine deficiency effects on trophic metabolism and water balance in the cockroach, Blaberus discoidalis

Unoperated, sham-operated (SO) and allatectomized (CA⁻) adult, male Blaberus discoidalis lost ca. 300 mg of live weight (LW) during the first 10 days after ecdysis. This decrease resulted from losses in both dry weight (DW) and water. An additional 100 mg LW loss was found in allatectomized-cardiacectomized (CA⁻+CC⁻) animals as a result of increased water loss.The LWs of operated and unoperated controls remained nearly constant between 10 and 30 days of age as DW increased and water decreased in comparable amounts. However, the LW of 30-day-old CA⁻+CC⁻ animals was 100 mg greater than the controls due to increased water retention.Compared to controls, food consumption and faecal production were reduced by 50 per cent in CA⁻ and CA⁻+CC⁻animals, but the percentage of food digested was unchanged. Efficiency of converting food to DW in CA⁻+CC⁻animals was twice that of SO and CA⁻ animals and four times that of the unoperated controls.These results indicate that extirpation of the retrocerebral complex decreases food intake but not digestion. Nutrient storage or conversion to body matter is apparently enhanced by neuroendocrine deficiency. Therefore, a gross nutritional deficiency is unlikely in CA⁻+CC⁻animals.The LW changes occurring after neuroendocrine deficiency were related to changes in water content. DW changes were comparable in all control and experimental groups. The results indicate both diuretic and antidiuretic effects by the neuroendocrine system depending on the age of the animals.     

Mitochondrial-driven sustained active water vapour absorption (WVA) in the firebrat, Thermobia domestica (Packard), during development and the moulting cycle

Rapid pre-functional mitochondrial biogenesis in the short-lived first-instar nymph occurs in the cells of the developing posterior rectal sacs which when mature are the organs believed to be responsible for sustained active water vapour absorption (WVA) in the firebrat Thermobia domestica (Packard). During the second instar, the mitochondria migrate apically and begin to associate with deep portasome-studded infolds of the apical plasma membrane (apm), just as WVA starts sporadically. By mid to late in the third instar the mature mitochondria-apm apical complex is fully developed, with elongated tubular mitochondria vertically packed hexagonally in transverse section and adpressed to the deeply pleated infolds of the apm, giving the greatest known concentration of mitochondria. This coincides with peak mass-specific WVA. During moults, WVA temporarily ceases as the sac cells secrete a new cuticle overlying the sac epithelium. Their apical complex fully regresses. Mitochondria migrate perinuclearly. The apm is pinched-off into numerous small portasome-studded pouches which remain sequestered within the cytoplasm. Towards the end of the moult the apm pouches reassemble into deeply pleated infolds into which the mitochondria migrate and elongate, rapidly re-establishing the hexagonal array of the apical complex. This coincides with the recommencement of WVA.     

Haemolymph lipase activity in the American cockroach, Periplaneta americana

The haemolymph of the cockroach, Periplaneta americana, has been shown to possess pronounced lipolytic activity. The enzyme may be considered a ‘true’ lipase because of its ability to hydrolyse long chain fatty acid glycerides. The enzyme exhibits dual optima at pH 4·9 and 7·0 and is inhibited by fluoride ion. Lipase activity in the intact cockroach is unaffected by the corpus cardiacum hypolipemic factor; however, prolonged periods of starvation result in a significant decline in enzyme activity.     

One trial learning in the American cockroach, Periplaneta americana

A new and simple method of training intact cockroaches was designed. (1) Cockroaches were maintained before and during the experiment with a high motivation to look for sugar. They were kept in a chamber with water and yeast extract ad libitum but without any sugar. (2) Cockroaches were individually trained to associate two artificial scent signals, i.e. menthol and vanilla, with sugar and salt solutions. Discriminatory learning performance was measured by testing the scent preference before and after training. Care was taken to exclude other than olfactory cues in the discriminatory paradigm. (3) Cockroaches exhibited a spontaneous initial preference for vanilla over menthol. This preference could be modified by training. The insect showed fast learning and long retention. One training trial was enough to reverse the initial preference with a significant retention after 7 days. Reversal of trained preference was accomplished by retraining. (4) The method provides an opportunity to study sensory performance and memory consolidation in cockroaches.     

Correlates of subordinate behaviour in the cockroach, Nauphoeta cinerea

Some characteristics of the dominant-subordinate relationship in the cockroach Nauphoeta cinerea were determined. Dominance could be reversed by experience with other animals, and individual recognition did not play a role in maintaining the relationship. The initial effects of subordination disappeared with increasing periods of separation before re-pairing and reversal may be observed. Exposure to artificial stress reversed the behaviour of both dominant and subordinate. A physiological correlate of subordinate behaviour was found. The results are related to current theories on insect stress physiology.     

Cellular differentiation in relation to water vapour absorption in the rectal complex of the mealworm, Tenebrio molitor

Larvae of the mealworm beetle Tenebrio molitor, are able to absorb water vapour from subsaturated air, but adults cannot. This functional difference is paralleled by structural differences in the cryptonephridial rectal complex, the site of vapour absorption in the larva. Very distinctive differences occur in the rectal pad epithelium and these are reported in detail for the first time. The cells of the larval rectal pad are very closely apposed, forming a structural, and presumably functional, unit, whereas the cells of the adult rectal pad are more clearly separate. Intracellular organization also shows clear differences. These differences indicate that the rectal epithelium may play a more important role in vapour absorption than recently ascribed to it. Other, less striking, differences in the cryptonephric Malpighian tubules and perinephric membrane as previously recorded have largely been confirmed. Morphometric analysis suggests that diffusion alone could account for the observed absorption of water vapour across the larval system from rectal lumen to the lumen of the cryptonephric tubules, but this does not rule out the possibility that other transporting mechanisms are also involved. Radial diffusion and antero-posterior gradients may be facilitated by the predominently radial and circumferential arrangement of the rectal pad cells and the surrounding cryptonephric tubules. Reinvestigation of the isolating perinephric membrane and its insertion onto the rectal cuticle supports the conclusions that insertion occurs only posteriorly. The model incorporating anterior as well as posterior insertion does not apply. The membrane posteriorly encloses a single perirectal space between rectum and tubules and in this region no perinephric or peritubular space is found between inner and outer regions of the membrane. This is the region where maximal gradients occur across the system.     

Induction of egg diapause in Bombyx mori by some cephalo-thoracic organs of the cockroach, Periplaneta americana

Induction of egg diapause in the silkworm, Bombyx mori by some cephalo-thoracic organs of the cockroach, Periplaneta americana was examined. All tissues tested such as brain, corpora cardiaca, corpora allata, suboesophageal and thoracic ganglia and nerve cords between thoracic ganglia were able to produce diapause eggs in non-diapause egg producers both by transplantation and injection of their crude homogenates. The homogenate of thoracic ganglia was effective even in pharate adults with the suboesophageal ganglion removed or in isolated abdomens of pharate adults.From these results, it was surmised that some endocrine organs, as well as the central nervous system in the cephalo-thorax of Periplaneta americana, contained the active principle responsible for egg diapause in Bombyx mori.     

Endotoxin-induced behavioural fever in the Madagascar cockroach, Gromphadorhina portentosa

Injections of a suspension of E. coli into the haemocoel of Gromphadorhina portentosa induced dose-dependent behavioural fevers. Cockroaches injected with bacteria and placed in a thermal gradient preferred temperatures significantly elevated over those chosen by control cockroaches. The fever response could also be induced by the injection of bacterial endotoxin, lipopolysaccharide-W. This is the first indication that insects are capable of febrogenesis.     

Partitioning of transpiratory water loss of the desert scorpion, Hadrurus arizonensis (Iuridae)

Terrestrial arthropods lose body water to the environment mainly through transpiration. The aim of this study was to determine the fraction of respiratory losses from total transpiratory water loss in scorpions, as relatively high respiratory losses would indicate a fitness benefit from regulation of gas-exchange rate under stressful desiccating conditions. We measured metabolic rates and water-loss rates of Hadrurus arizonensis (Iuridae) at a range of ecologically-relevant temperatures. Calculation of respiratory water losses was based on increased metabolic and water-loss rates during nocturnal activity (assuming no change in cuticular resistance at a given constant experimental temperature). Respiratory losses accounted for 9.0 ± 1.7% of total transpiratory losses at 25 °C, doubled to 17.9 ± 1.8% at 30 °C and increased to 31.0 ± 2.0% at 35 °C (n = 5, 15 and 15, respectively). Furthermore, the relative importance of respiratory transpiration is likely to be higher at temperatures above 35 °C, which have been recorded even within the burrows of H. arizonensis. Measurements of cuticular lipid melting points do not provide evidence for increased cuticular resistance to water loss at higher temperatures. However, the relatively high fraction of respiratory water losses reported here for H. arizonensis supports the notion of respiratory regulation as an evolved mechanism for conserving scorpion body water stores under stressful conditions.     

Development of the circadian clock in the German cockroach, Blattella germanica

The cell distribution and immunoreactivity (ir) against period (PER), pigment dispersing factor (PDF) and corazonin (CRZ), were compared between adults and nymphs in the central nervous system of the German cockroach. Although PER-ir cells in the optic lobes (OL) were expressed in the nymphs from the first instar, the links between major clock cells became more elaborated after second/third instar. A circadian rhythm of locomotion was initiated at the fourth/fifth instar. The results suggest that the clock was running from hatching, but the control network needed more time to develop. In addition, the putative downstream regulators, PDF-ir and CRZ-ir, are co-localized in various regions of the brain, indicating potential output routes of the circadian clock. CRZ-ir cells with typical morphology of neurosecretory cells in the dorsolateral protocerebrum send out three neural fibers to reach the ipsilateral corpora cardiaca (CC), the antennal lobe and two hemispheres of the protocerebrum. Based on co-localization with some PER-ir/PDF-ir cells, the CRZ-ir cells have the potential to serve as a bridge between circadian neural signals and endocrine regulation. Based on PDF's role in the regulation of locomotion, our results support the finding that the locomotor circadian rhythm is possibly controlled by a hormonal route.     

Serotonin in the central nervous system of the cockroach, Periplaneta americana

Studies on serotonin in the insect nervous system has long been neglected, although serotonin is a putative neurotransmitter. During the course of this study the serotonin content was found to be significantly higher than that found in mammalian midbrain. Parachlorophenylalanine was found to inhibit the first step of the biosynthetic pathway by inhibiting tryptophan-hydroxylase enzyme and leading to alterations in the concentrations of metabolites such as 5-hydroxy tryptophan, 5-hydroxy indole acetic acid and tryptophan. Using a dose of 15 μg/g the inhibitory effect was not long lasting and recovery was observed to restore the normal levels. Higher trytophan levels were observed after a certain period of P-chlorophenylalanine treatment because there was a block in the biosynthetic path and tryptophan could not be utilized for 5-HT synthesis. A negative correlation between brain tryptophan and protein content was observed in both the cases of P-chlorophenylalanine and reserpine treatments.     

Circadian rhythmicity in the nervous system of the cockroach, Periplaneta americana

Diurnal rhythmicity of nervous activity in Periplaneta americana was investigated, using acetylcholine (ACh) content, acetylcholinesterase (AChE) and spontaneous electrical activities as indices. AChE and electrical activities were maximum at 0 hr and minimum at 12 hr, while ACh showed an opposite rhythm. Central nervous system extract from cockroaches at 12 hr elevated the electrical activity while 0 hr-extract exerted inhibition. Lower concentrations of ACh had an elevatory influence while higher concentrations inhibited the electrical activity. A hypothesis is proposed, suggesting synthetic and releasing phases of ACh in a regular diurnal cycle, to explain the results obtained.     

The inhibition of milk synthesis by juvenile hormone in the viviparous cockroach, Diploptera punctata

The brood sac of the viviparous cockroach, Diploptera punctata, synthesizes a protein rich milk which nourishes developing embryos. Milk is first detected in the brood sac (by immunoelectrophoresis) when the embryos begin drinking and continues to increase in parallel with total protein of the brood sac. When embryos cease drinking, both total protein and milk decline in the brood sac. Premature decline in protein and milk content of the brood sac has been observed after treatment with juvenile hormone (from implanted active corpora allata) or a juvenile hormone analogue (ZR 512 applied topically). The fine structure of the brood sac 7 days after corpora allata implant is consistent with that of gland cells which are not actively synthesizing milk. The effect of ZR 512 is detected in decreased milk content of the brood sac after 24 hr of treatment.     

Functional analysis of Scr during embryonic and post-embryonic development in the cockroach, Periplaneta americana

The cockroach, Periplaneta americana represents a basal insect lineage that undergoes the ancestral hemimetabolous mode of development. Here, we examine the embryonic and post-embryonic functions of the hox gene Scr in Periplaneta as a way of better understanding the roles of this gene in the evolution of insect body plans. During embryogenesis, Scr function is strictly limited to the head with no role in the prothorax. This indicates that the ancestral embryonic function of Scr was likely restricted to the head, and that the posterior expansion of expression in the T1 legs may have preceded any apparent gain of function during evolution. In addition, Scr plays a pivotal role in the formation of the dorsal ridge, a structure that separates the head and thorax in all insects. This is evidenced by the presence of a supernumerary segment that occurs between the labial and T1 segments of RNAiScr first nymphs and is attributed to an alteration in engrailed (en) expression. The fact that similar Scr phenotypes are observed in Tribolium but not in Drosophila or Oncopeltus reveals the presence of lineage-specific variation in the genetic architecture that controls the formation of the dorsal ridge. In direct contrast to the embryonic roles, Scr has no function in the head region during post-embryogenesis in Periplaneta, and instead, strictly acts to provide identity to the T1 segment. Furthermore, the strongest Periplaneta RNAiScr phenotypes develop ectopic wing-like tissue that originates from the posterior region of the prothoracic segment. This finding provides a novel insight into the current debate on the morphological origin of insect wings.     

Seasonal thermoregulation in the burrowing parrot (Cyanoliseus patagonus)

Birds exposed to seasonal environments are faced with the problem of maintaining thermogenic homoeostasis. Previous studies have established that birds native to the Holarctic increase their Resting Metabolic Rate at different ambient temperatures (RMR_Ta) and Basal Metabolic Rate (BMR) in winter as an adaptation to cold temperature since winters are more severe, while their non-Holarctic counterparts generally decrease their winter BMR as an energy saving mechanism during unproductive and dry winter months. In this study, we examined seasonal thermoregulation in the burrowing parrot (Cyanoliseus patagonus), a colonial psittacine native to the Patagonian region of Argentina, a region with an unpredictable environment. We found significantly higher mass specific RMR_Ta and BMR in summer than in winter. Both summer and winter BMR of the species fell within the predicted 95% confident interval for a parrot of its size. Body mass was significantly higher in winter than in summer. The burrowing parrot had broad thermo-neutral zones in winter and summer. The circadian rhythm of core body temperature (T_b) of burrowing parrots was not affected by season, showing that this species regulated its T_b irrespective of season. These results suggest that the burrowing parrots' seasonal thermoregulatory responses represent that of energy conservation which is important in an unpredictable environment.     

Cyclic gas exchange in the giant burrowing cockroach, Macropanesthia rhinoceros: effect of oxygen tension and temperature

The giant burrowing cockroach, Macropanesthia rhinoceros, is endemic to north-eastern Australia and excavates a permanent burrow up to 1m deep into soil. Using flow-through respirometry, we investigated gas exchange and water loss at three different oxygen tensions (21%, 10% and 2% at 20 degrees C) and temperatures (10, 20 and 30 degrees C at 21% oxygen). M. rhinoceros employ cyclic gas exchange (CGE) making the species by far the largest insect known to engage in discontinuous ventilation. CGE featured rhythmic bursts of CO(2) dispersed among inter-burst periods of reduced output. CGE was most commonly observed at 20 degrees C and degraded at <10% oxygen. Mild hypoxia (10% oxygen) resulted in a lengthening of the burst period by approximately two-fold; this result is complementary to oxygen consumption data that suggests that the burst period is important in oxygen uptake. When exposed to severe hypoxia (2% oxygen), CGE was degraded to a more erratic continuous pattern. Also, during severe hypoxia, total water loss increased significantly, although CO(2) release was maintained at the same level as in 21% oxygen. During CGE, an increase in temperature from 10 to 20 degrees C caused both water loss and CO(2) output to double; from 20 to 30 degrees C, CO(2) output again doubled but water loss increased by only 31%.