Hygroreceptor identification and response characteristics in the stick insectCarausius morosus

Summary Simultaneous recordings were made from 3 sensory units in an easily identifiable sensillum on the 12th antennal segment ofCarausius morosus. Impulse frequency (F) of one unit rose sharply when either the temperature (T) or the partial pressure of water vapor (Pw) was suddenly lowered. F of another rose sharply either when T was suddenly lowered or Pw was raised. F of the third was hardly affected by sudden changes in T but rose abruptly when Pw fell (Fig. 1). The reactions of the first may be explained by enthalpic cooling and is considered a cold cell. Those of the second may be attributed to changes in relative humidity (Hr) and is thus termed a moist cell. The third is taken to be the latter's antagonist, a dry cell.A 90%-probability that a single moist cell of average differential sensitivity will correctly discriminate between two humidity levels is not reached until the difference between the two is 38% Hr. The dry cell requires a difference of only 7.5% (Table 1). The basis for discrimination is a single presentation of each level.The power to discriminate Hr steps is better in both cell types. For a single moist cell of average differential sensitivity the difference required between the steps for a 90%-probability of correct discrimination is only 6.3% Hr; for the dry cell, 3.5% Hr. Basis for discrimination: a single presentation of each step. Step range: 5% to 55% Hr.Abbreviations F impulse frequency in impulses per second (imp/s) - Hr orHR relative humidity in % - Ps saturation pressure of water vapor in torr - Pw partial pressure of water vapor in torr - r correlation coefficient - T temperature in °C Dedicated to Prof. Dr. F. Schaller on the occasion of his 65th birthday     

The Evaporative Function of Cockroach Hygroreceptors

Insect hygroreceptors associate as antagonistic pairs of a moist cell and a dry cell together with a cold cell in small cuticular sensilla on the antennae. The mechanisms by which the atmospheric humidity stimulates the hygroreceptive cells remain elusive. Three models for humidity transduction have been proposed in which hygroreceptors operate either as mechanical hygrometers, evaporation detectors or psychrometers. Mechanical hygrometers are assumed to respond to the relative humidity, evaporation detectors to the saturation deficit and psychrometers to the temperature depression (the difference between wet-bulb and dry-bulb temperatures). The models refer to different ways of expressing humidity. This also means, however, that at different temperatures these different types of hygroreceptors indicate very different humidity conditions. The present study tested the adequacy of the three models on the cockroach’s moist and dry cells by determining whether the specific predictions about the temperature-dependence of the humidity responses are indeed observed. While in previous studies stimulation consisted of rapid step-like humidity changes, here we changed humidity slowly and continuously up and down in a sinusoidal fashion. The low rates of change made it possible to measure instantaneous humidity values based on UV-absorption and to assign these values to the hygroreceptive sensillum. The moist cell fitted neither the mechanical hygrometer nor the evaporation detector model: the temperature dependence of its humidity responses could not be attributed to relative humidity or to saturation deficit, respectively. The psychrometer model, however, was verified by the close relationships of the moist cell’s response with the wet-bulb temperature and the dry cell’s response with the dry-bulb temperature. Thus, the hygroreceptors respond to evaporation and the resulting cooling due to the wetness or dryness of the air. The drier the ambient air (absolutely) and the higher the temperature, the greater the evaporative temperature depression and the power to desiccate.     

Environmental conditions and their impact on immunocompetence and pathogen susceptibility of the Caribbean termite Nasutitermes acajutlae

1. Little is known about interactions between environmental conditions surrounding insects and their immune responses. 2. The environment in and around termite colonies, including temperature, relative humidity, soil pH, and light was analysed using principal components analysis (PCA). 3. The relationship between these abiotic parameters and two aspects of termite immunity (phenoloxidase activity and lipid content) was examined in field‐caught workers of Nasutitermes acajutlae Holmgren. Finally, termites from warm/dry and cool/moist habitats were exposed to Metarhizium anisopliae to determine their susceptibility to mycosis. 4. PCA indicated that environmental components external to the nest [ambient temperature, ambient relative humidity (RH), soil temperature and light] comprised the majority (PC1 = 37.5%) of variation. Internal variables (nest temperature and RH) and nest volume accounted for 19.6% (PC2) of the variation with pH comprising 12.9% (PC3). 5. AIC and regression models suggested that ambient temperature was most strongly and positively associated with immune variables and that relative humidity may also play a role. Termites from warm/dry colonies were less susceptible to M. anisopliae than termites from cool/moist colonies. 6. Thus, termites nesting in warmer habitats may exhibit increased immune‐related measures and reduced susceptibility to mycosis compared with termites from cooler habitats.     

Low rates of change enhance effect of humidity on the activity of insect hygroreceptors

The inability to measure humidity during stimulation has so far prevented us from understanding the contribution of moist cells and dry cells to orientation in a gradient of humidity. The problem was solved in the present study by means of a UV-absorption hygrometer that made it possible to monitor humidity at a rate of 100 Hz. The antennal moist and dry cells of the cockroach were exposed to humidities alternatively falling or rising at low rates between -1% RH s(-1) and +1% RH s(-1) (relative humidity). Impulse frequency of both types of cells depended simultaneously on instantaneous humidity and its rate of change. High frequencies of the moist cells signal high humidity. But at a given humidity, the response frequency is higher still when humidity is also rising. Conversely, high frequencies of the dry cell signal low humidity, and frequency is higher still at a given humidity when humidity is also falling. These responses ensure that the cockroach spent a minimum time in environments where desiccation or hydration occur and may thus protect the animal from emerging accidentally from under cover into moving air. In the constant-humidity retreat of the cockroach, fluctuating or even drifting discharge frequencies could serve as an early warning: return!     

Effect of inspired air conditions on exercise-induced bronchoconstriction and urinary CC16 levels in athletes

Injury to the airway epithelium has been proposed as a key susceptibility factor for exercise-induced bronchoconstriction (EIB). Our goals were to establish whether airway epithelial cell injury occurs during EIB in athletes and whether inhalation of warm humid air inhibits this injury. Twenty-one young male athletes (10 with a history of EIB) performed two 8-min exercise tests near maximal aerobic capacity in cold dry (4°C, 37% relative humidity) and warm humid (25°C, 94% relative humidity) air on separate days. Postexercise changes in urinary CC16 were used as a biomarker of airway epithelial cell perturbation and injury. Bronchoconstriction occurred in eight athletes in the cold dry environment and was completely blocked by inhalation of warm humid air [maximal fall in forced expiratory volume in 1 s = 18.1 ± 2.1% (SD) in cold dry air and 1.7 ± 0.8% in warm humid air, P < 0.01]. Exercise caused an increase in urinary excretion of CC16 in all subjects (P < 0.001), but this rise in CC16 was blunted following inhalation of warm humid air [median CC16 increase pre- to postchallenge = 1.91 and 0.35 ng/μmol in cold dry and warm humid air, respectively, in athletes with EIB (P = 0.017) and 1.68 and 0.48 ng/μmol in cold dry and warm humid air, respectively, in athletes without EIB (P = 0.002)]. The results indicate that exercise hyperpnea transiently disrupts the airway epithelium of all athletes (not only in those with EIB) and that inhalation of warm moist air limits airway epithelial cell perturbation and injury.     

Domatia morphology and mite occupancy of Psychotria horizontalis (Rubiaceae) across the Isthmus of Panama

Leaf domatia are small plant structures in vein axials on the undersides of leaves that are often inhabited by mites of several species. The mites are presumed to benefit the plant because they are predatory or fungivorous. The domatia are thought to provide the mites shelter from predators and changes in relative humidity, and in exchange, the mites protect the plant from small herbivores and fungal spores. Differences in relative humidity can affect food availability, changing the interaction between plants and mites. We examined domatium morphology of the shrub Psychotria horizontalis (Rubiaceae) and its associated mite diversity at three sites along the rainfall gradient of the Isthmus of Panama, during the dry and wet seasons. The dry forest had a domatium morphology consistent with providing greater desiccation protection, with trichomes and a smaller domatium opening relative to domatium size (size/opening ratio). Additionally, this size/opening ratio was significantly higher in the dry season than in the wet season at all three sites. Mite diversity was highest at the intermediate rainfall site with a large degree of overlap with the other sites, whereas the dry site and wet site shared few mite species. More fungivorous mites were present in the moist forests and more facultative feeders on fungal spores and small mites in the dry forest. The average mite size at each site matched the average domatium size at each site. The dry forest had small mites in small domatia, whereas the moist forests had larger mites in larger domatia. While these data are primarily observational, the site and seasonal differences in domatium morphology and mite diversity are consistent with two main hypotheses: (1) that protection from changes in humidity would be particularly important when humidity was low, such as in the dry forest and during the dry season (2) more fungivorous mites would be found in domatia of the moist forests. The data presented here further highlight the close adaptive relationship between leaf domatia on plants and the mites that inhabit them.     

Age-dependent response of boreal forest to temperature and rainfall variability

We used measurements of CO₂ exchange by six Canadian boreal forest stands to determine how sites of contrasting age respond to interannual temperature and precipitation variation. The stands ranged in age (time since last burn) from 4 to 155 years. The study included years that were anomalously cool and moist, warm and dry, cool and dry, and warm and moist. Warmer than average springs accelerated the onset of older stand (> 20 years) photosynthesis by as much as 37 days and younger stand (< 20 years) photosynthesis by as much as 25 days. The warm–dry year resulted in a marked reduction of mid‐summer CO₂ uptake by the younger, but not older, stands. The mid‐summer decline in young stand photosynthesis reflected the combination of warmth and drought; similar declines were not observed during the cool–dry or warm–moist years. The annual carbon gain by the oldest stands was greatest during the warm–dry year as a result of the expanded growing season. The annual carbon gain by the youngest stands was consistent from year to year, largely as a result of offsets between increased spring photosynthesis and reduced mid‐summer photosynthesis during the warm–dry year. Night‐time CO₂ efflux increased by 2–29% during the warm–moist year relative to the warm–dry year. This increase was not systematically related to age. We conclude that the major source of interannual CO₂ exchange variation at the landscape scale is the ability of older, evergreen canopies to respond to warm springs by advancing the onset of photosynthesis. Drought‐related reductions in photosynthesis, moisture‐driven respiratory losses, and the effects of spring warmth on young‐stand photosynthesis are of secondary importance. The advantage conferred on older, evergreen stands during warmer years carries implications for the possible effects of climate change on boreal forest succession. Warmer temperatures may increase the competitive advantage of late successional species relative to early successional species, and also the incidence of fire, thereby accelerating plant succession and shortening the fire‐return interval.     

Microclimate,diurnal rhythms and the conquest of the land by arthropods

Summary A review is given of the adaptations of arthropods to life on land. The terrestrial Arthropoda are divided ecologically into two main groups. The first of these includes woodlice, centipedes, miilipedes and their allies which lose water rapidly in dry air and consequently are restricted to damp, dark habitats which they leave only at night when the temperature falls and the relative humidity of the air rises. The second group includes most insects and Arachnida: these are comparatively independent of moist surroundings because their integument possesses an impervious layer of wax which prevents desiccation.     

A technique to measure the ability of the human nose to warm and humidify air.

To assess the ability of the nose to warm and humidify inhaled air, we developed a nasopharyngeal probe and measured the temperature and humidity of air exiting the nasal cavity. We delivered cold, dry air (19-1 degrees C, <10% relative humidity) or hot, humid air (37 degrees C, >90% relative humidity) to the nose via a nasal mask at flow rates of 5, 10, and 20 l/min. We used a water gradient across the nose (water content in nasopharynx minus water content of delivered air) to assess nasal function. We studied the characteristics of nasal air conditioning in 22 asymptomatic, seasonally allergic subjects (out of their allergy season) and 11 nonallergic normal subjects. Inhalation of hot, humid air at increasingly higher flow rates had little effect on both the relative humidity and the temperature of air in the nasopharynx. In both groups, increasing the flow of cold, dry air lowered both the temperature and the water content of the inspired air measured in the nasopharynx, although the relative humidity remained at 100%. Water gradient values obtained during cold dry air challenges on separate days showed reproducibility in both allergic and nonallergic subjects. After exposure to cold, dry air, the water gradient was significantly lower in allergic than in nonallergic subjects (1,430 +/- 45 vs. 1,718 +/- 141 mg; P = 0.02), suggesting an impairment in their ability to warm and humidify inhaled air.     

Bacterial pleomorphism and competition in a relative humidity gradient

The response of different bacterial species to reduced water availability was studied using a simple relative humidity gradient technique. Interestingly, distinct differences in morphology and growth patterns were observed between populations of the same species growing at different relative humidity. Gram-positive cocci increased in cell size as they approached humidity growth limits and staphylococcal species started growing in tetrad/cubical formations instead of their normal grape-like structures. Gram-negative rods displayed wave-like patterns, forming larger waves as they became increasingly filamentous at low humidity. In contrast, cells of the Gram-positive bacterium Bacillus subtilis became shorter, curved, and eventually almost coccoid. Moreover, B. subtilis started to sporulate at low humidity. The altered morphology and/or growth patterns of bacteria growing at low humidity might be more ecologically relevant than their textbook appearance at high humidity since their natural habitats are often dry. Transmission electron microscopic analyses revealed that staphylococci grown at low humidity have significantly thickened cell walls, which may explain why these cells displayed increased resistance to vancomycin. We conclude that our relative humidity gradient technique is widely applicable for investigating effects of relative humidity on microbial survival, growth and competitive success at solid–air interfaces, making it a versatile tool in microbial ecology.     

Desiccation and thermal tolerance of eggs and the coexistence of competing mosquitoes

We tested the hypothesis that differences in temperature and desiccation tolerances of eggs of the container-dwelling mosquitoes Aedes albopictus and Aedes aegypti influence whether invading A. albopictus coexist with or exclude A. aegypti in Florida. In the laboratory, egg mortality through 30 days for A. albopictus was strongly temperature and humidity dependent, with low humidity and high temperature producing greatest mortality. In contrast, mortality through 30 days and through 60 days for A. aegypti was very low and independent of temperature and humidity. Mortality through 90 days for A. aegypti showed significant effects of both temperature and humidity. In the field, the proportion of vases occupied by A. albopictus was significantly lower at four of six sites at the start of the wet season (after a dry period) versus well into the wet season (after containers had held water for weeks). The proportion of vases occupied by A. aegypti was independent of when during the wet season vases were sampled. These results imply that dry periods cause disproportionately greater mortality of A. albopictus eggs compared to A. aegypti eggs. Container occupancy at tire and cemetery sites was significantly related to two principal components derived from long-term average climate data. Occupancy of containers by A. albopictus was greatest at cool sites with little or no dry season, and decreased significantly with increasing mean temperature and increasing number of dry months. In contrast, occupancy of containers by A. aegypti was lowest at cool sites with little or no dry season, and increased significantly with increasing mean temperature and increasing dry season length, and decreased significantly with total precipitation and number of wet months. We suggest that local coexistence of these species is possible because warm, dry climates favor A. aegypti and alleviate effects of competition from A. albopictus via differential mortality of A. albopictus eggs.     

Plasticized waxy maize starch: effect of polyols and relative humidity on material properties

The plasticizing effect of different polyols such as glycerol, xylitol, sorbitol, and maltitol on waxy maize starch was investigated. The concentration of plasticizer was fixed at 33 wt % (dry basis of starch). The structure and mechanical performance of resulting films conditioned at different relative humidity levels were studied in detail. The effect of the plasticizer on the glass-rubber transition temperature (T(g)) and crystallinity was characterized using differential scanning calorimetry. It was found that T(g) decreases with increasing moisture content and decreasing molecular weight of the plasticizer. The water resistance of starch increased steadily with the molecular weight of the plasticizer and was directly proportional to the ratio of the end to total hydroxyl groups. As the molecular weight of the plasticizer increased, the brittleness of the dry system increased. However, the use of high molecular plasticizer allowed good mechanical properties of the moist material to be obtained in terms of both stiffness and elongation at break.     

The influence of weather on asthma in Nairobi

The frequency of bronchial asthma in Nairobi is related to meteorological parameters such as relative humidity, rainfall, dew point temperature, hours of sunshine and dry bulb temperature. Two seasons were taken for study: one cold season (May–August 1975) and one relatively warm season (December 1975–March 1976). It was found that significant correlations occurred at a lag of 2 or 3 days, but not at a lag of 4 or 5 days. Cold and wet weather during the cold season and heat of the day and dryness of the atmosphere during the warm season aggravate asthma in Nairobi.. The frequency of asthmatic attacks is about the same during the two seasons, but the intensity of suffering of a greater majority of patients is more in cold and wet weather than in warm and dry weather. 20–25% of the patients do not feel any relationship between weather and their asthmatic troubles. Nearly twice as many patients suffer from cough with the production of sputum in the cold season than in the warm season. About three times as many patients suffer from bronchospasm in the cold season than in the warm season. Severe asthmatic attacks occur almost equally in both the seasons.     

Solenostoma oblongifolium (K. Müll.) K. Müll. in Scotland—new to the British Isles

Abstract

To determine the responses of cryptogams to the variations in temperature, pH, and humidity, we studied the vegetation of Thermal Meadow, Hotsprings Island, Queen Charlotte Islands, B.C., Canada. Only seven cryptogamic taxa were present in the samples: five mosses, one liverwort, and one lichen. Humidity limited the distribution, with Racomitrium lanuginosum and Cladina ciliata preferring the warmer, drier sites and Pleurozium schreberi and Dicranum scoparium preferring cooler, more moist sites. Polytrichum formosum was the most frequent taxon, occurring under both cool, moist conditions and warm, dry conditions. Aulacomnium palustre occurred in the mid temperature range mostly where humidity was fairly high. The pH ranged 6.8–7.2, providing insufficient variation for us to delimit species preferences.     

Integrated control of two spotted spider mite,Tetranychus urticae on cucumber grown under plastichouse conditions in egypt

Microclimatic conditions were monitored in cucumber grown under unheated plastichouses in three consecutive years, i.e. from 1990 to 1992 in Egypt. The relative humidity in the plastichouses constructed on either sandy or clay soil did not exceed 30% during mid-day time, while the average temperature did not drop below 30°C. Such conditions favoured population build up of the two spotted spider miteTetranychus urticae Koch. In 1993 and 1994, three plastichouses planted to cucumber, cultivar Rawa or Hana were selected. Relative humidity in two of them was maintained over 50% during the day using spraying nozzles, the third being kept as control. Mildew diseases induced by increased leaf wetness needed to be managed using fungicides.Phyioseiulus persimilis andP. longipes were released in the first two plastichouses, while acaricides were applied in the control. In early MayT. urticae population increase on the growing top of cucumber plants required two acaricidal applications as predatory mites did not migrate to the apical leaves which were too warm and dry. More than 80% of the maximum yield was obtained on average in plastichouses using increased relative humidity, but without any acaricidal applications.     

Response characteristics of a spider warm cell: temperature sensitivities and structural properties

The sensitivity of a warm cell to temperature stimulation was examined electrophysiologically on the spider Cupiennius salei. The relationship between sensitivity and structure of the warm cell was assessed by comparing both the electrophysiological and electron-microscopic data with those described for insect cold cells. Stimulation of the spider warm cell with slowly oscillating temperature change and steady temperature elicited less sensitive responses than in insect cold cells. These characteristics are reflected in the size of the dendritic membrane area, which is smaller in the spider warm cell compared to the insect cold cells. Rapid step-like temperature change produced in the spider warm cell very sensitive responses when compared with data of insect cold cells. The dendritic tip of the spider warm cell is exposed at a pore on the tip of the sensillum but is covered by the cuticle of the sensillum in the insect cold cells.Dedicated to Richard Loftus on the occasion of his 70th birthday, who pioneered several of the questions addressed in this study     

Climatic signals from loess-soil sequences in the central Great Plains, USA

Late Quaternary eolian deposits and buried soils in the central Great Plains are interpreted to reflect the fluctuation of climatic conditions under which they formed. The Loveland Loess was deposited approximately between 500 and 100 ka. Within the loess are four zones of pedogenic carbonate accumulation: after 416 ± 35 ka; before 260 ± 25 ka; around 193 ± 22 ka; and before 92 ± 7.0 ka. The pedogenic carbonate zones were probably formed under warm and dry conditions. The moderately weathered Barton sand at the Barton section and the equivalent Sandy Silt II at other sections, deposited between 92 ± 7.0 and 69 ± 6.4 ka, suggest windy, probably warm, and fluctuating moisture consitions. A reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very low rate of loess deposition. Overlying the reddish pedocomplex is the Sandy Silt I, probably a stratigraphic equivalent to the Roxana Silt dated at 40−30 ka in the Central Lowlands. The Gilman Canyon Formation (35−20 ka), a thick cumulic loessial and organic-matter-rich pedocomplex, developed under relatively moist and probably cool conditions. The Peoria Loess was deposited at a very rapid rate under dry and cold conditions. The Brady Soil (10.5−8.5 ka) was formed under relatively warm and moist conditions. The poorly weathered Bignell Loess was deposited during the warm and dry Altithermal Period (9−5 ka).     

热带季节性湿润林苦楝(Melia azedarach)径向生长季节动态及其对环境因子的响应

气候变化导致的温度升高和降水格局改变可能会影响到树木的生长速率和季节物候。西双版纳热带季节性湿润林分布在石灰岩山中部,属于热带喀斯特生境。由于土层浅薄,土壤保水能力极差,植物生长更容易遭到受到季节性干旱气候的影响。为探究热带季节性湿润林的树木径向生长季节动态及其对环境因子的响应,利用高精度树木生长仪连续两年监测了云南西双版纳热带季节性湿润林中落叶树种苦楝（Melia azedarach）的树干径向变化,并与同步监测的环境因子进行相关分析。结果表明,苦楝径向生长开始、结束以及持续生长的时间在年际间存在差异。与2018年相比,2019年苦楝生长开始和结束的时间较晚,且年生长量较小,这可能是与2019年雨季开始较晚且在生长季早期经历了严重的高温干旱有关。苦楝的径向日生长量与日降水量和相对湿度呈正相关关系,与光合有效辐射、水汽压亏缺和风速呈负相关关系,表明了在苦楝的径向生长主要受水分条件限制。在干旱年份（2019年）,苦楝的日生长量与降水和相对湿度的相关性更强。研究结果有助于进一步了解热带喀斯特生境树木生长对气候变化的敏感性以及树木适应季节性干旱气候的策略。     

Cold spots in neonatal incubators are hot spots for microbial contamination

Thermal stability is essential for the survival and well-being of preterm neonates. This is achieved in neonatal incubators by raising the ambient temperature and humidity to sufficiently high levels. However, potentially pathogenic microorganisms also can thrive in such warm and humid environments. We therefore investigated whether the level of microbial contamination (i.e., the bacterial load) inside neonatal incubators can be predicted on the basis of their average temperature and relative humidity settings, paying special attention to local temperature differences. Swab samples were taken from the warmest and coldest spots found within Caleo incubators, and these were plated to determine the number of microbial CFU per location. In incubators with high average temperature (≥ 34°C) and relative humidity (≥ 60%) values, the level of microbial contamination was significantly higher at cold spots than at hot spots. This relates to the fact that the local equilibrium relative humidity at cold spots is sufficiently high to sustain microbial growth. The abundance of staphylococci, which are the main causative agents of late-onset sepsis in preterm neonates, was found to be elevated significantly in cold areas. These findings can be used to improve basic incubator hygiene.     

The effect of nest moisture on daily temperature regime in the nests of Formica polyctena wood ants

Summary: Relations between nest moisture and daily temperature regime were studied. Two extreme situations were distinguished among the variable patterns of daily temperature regime found. The first one was characterized by increasing temperature during the day and decreasing temperature during the night and was typical for dry nests exposed to sun. The second one was characterized by a lower temperature during the day that increased rapidly during the night. This pattern occurred in moist shaded nests and was less frequent than the first one.¶Patterns of surface nest temperature, which closely correspond with thermal loss, differ between dry and wet nests as well. In dry nests, the temperature decreased during the night on the whole surface in a similar way. In moist nests, the top parts constantly had a high temperature. The average surface temperature during the night was significantly higher in moist than in dry nests, which implies a higher thermal loss in moist nests. Microbial respiration of nest material strongly correlated with nest moisture, which implies a higher microbial heat production in moist nests.¶The results indicated two mechanisms for the maintenance of internal nest temperature. The first one, used in dry nests, is based on a combination of ant metabolic heat production and the isolation properties of a dry nest. The second one, used in moist nests, is based on the metabolic heat production provided by both the ants and the microorganisms in the nest material. These two strategies differ in the pattern of daily temperature fluctuation.