Population dynamics and dispersal of Lepthyphantes tenuis in an ephemeral habitat

The population dynamics of Lepthyphantes tenuis (Blackwall) were investigated in two fields of winter wheat in Sussex, England, with the aim of attributing the major factors controlling population fluctuations. Continuous measures of changes in density, reproductive rate and dispersal were obtained using a range of methodologies, including laboratory analysis, suction trapping, rotary sampling of the aerial fauna, caging, and detailed density estimations. The resulting data were then used to determine the major causes of the observed population fluctuations and to describe the processes of dispersal and reproduction in this population.Population densities were initially very low following ploughing operations, but increased throughout the season as a result of high reproductive rates. Investigation of the reproductive potential of the spiders showed that the number of eggs per egg-sac did not vary with season, and that egg development was temperature related. There was no evidence that the number of viable eggs per egg-sac varied during the season. There were three peaks of hatchling production per year suggesting two to three generations of spiders. Dispersal was not responsible for the major changes in field density throughout the season although dispersal activity was high for this species. Dispersal activity increased with age and was highest in females. Dispersal activity as a ratio of activity/field density for females, males, sub-adults, immatures and hatchlings was 4:2:3:1:1.Aerial dispersal is only possible under suitable weather conditions. It was found that female dispersal was correlated with weather conditions far more strongly than other population groups. Calculations showed that under suitable weather conditions (e.g., 25% of the time being suitable for dispersal), almost 4% of the adult females could be expected to leave the population daily. The overall effect is therefore to displace individuals from the population but to have little effect on densities. Dispersal in other stages was controlled by the suitability of weather conditions but also by other, undetermined factors. It is postulated that L. tenuis has a life history strategy whereby suitable habitats act as sources of spiders, mainly females, which are continually involved in dispersal. Dispersal in other population groups may be triggered by factors such as the avoidance of adverse conditions. This type of life-history strategy is typical of organisms, such as weeds, that are successful in ephemeral habitats and may indicate that this species originally evolved in unpredictable habitats such as dry river beds or coastal areas.     

Weather variability impacts on oviposition dynamics of the southern house mosquito at intermediate time scales

Oviposition is a major event in the life history of mosquitoes, shaping both individual fitness and vectorial capacity. Several exogenous factors have been shown as important for the dynamic forcing of oviposition at finely (hourly) and coarsely (monthly or season to season) grained temporal scales. However, field studies addressing the interplay of weather factors on oviposition dynamics at the intermediate (days to weeks) time scale are missing. Here, we present the results from a field study that showed the oviposition dynamics of the southern house mosquito, Culex quinquefasciatus Say (Diptera: Culicidae), to be: (i) primarily dictated by relative humidity; and (ii) disrupted by rainfall events that resulted in a modified sensitivity to relative humidity. Rainfall changed the concentration of ammonia, a major limiting resource of microbes used as food by mosquito larvae. Following major rainfall events, the importance of relative humidity in forcing the oviposition dynamics also changed. Finally, our results indicate that qualitative changes in oviposition habitats modify the importance of weather variables as predictors of mosquito oviposition dynamics.     

Drivers of hybridization in a 66-generation record of Colias butterflies

Hybridization significantly affects the ecology and evolution of numerous plant and animal lineages. Most studies have focused on endogenous drivers of hybridization and neglected variation in exogenous factors, such as seasonal weather patterns. In this study, we take advantage of a unique dataset consisting of records of hybridization between the butterflies Colias eurytheme and C. eriphyle (Pieridae) for 66 generations (22 years) to investigate the importance of seasonal weather on the production and survival of hybrid offspring. Important seasonal weather variables for each parental species and hybrid offspring were determined using model averaging, and these weather variables, along with butterfly abundances, were analyzed using path analysis. The most important drivers of hybridization were the abundance of C. eriphyle, summer minimum temperature, and spring maximum temperature. In contrast, the abundance of C. eurytheme and weather variables prior to the current flight season were relatively unimportant for variation in hybrid abundance. Parental abundances were mostly driven by weather variables prior to the flight season possibly because these variables affect host plant quality. Our results suggest that exogenous, climatic factors can influence hybridization in natural systems, and that these factors can act both directly on hybrid abundance and indirectly through the population dynamics of parental species.     

环境因子对民勤绿洲荒漠过渡带梭梭人工林蒸散的影响

利用涡度相关系统、土壤水分TDR传感器,于2014年7月—2015年6月连续测定了民勤绿洲荒漠过渡带退化梭梭人工林蒸散量,研究不同天气条件下梭梭人工林的蒸散对外界环境因子的响应.结果表明: 梭梭人工林晴天蒸散量日变化具有明显的季节变化规律.梭梭人工林蒸散量日变化幅度在生长季初期逐渐增大,在生长旺盛期达到最大峰值(0.07 mm·h^-1), 而后逐渐减小,至12月达到最低峰值(0.01 mm·h^-1).不同天气条件下梭梭人工林蒸散日变化波动幅度差异较大,阴天蒸散日变化波动幅度最小,降水后蒸散波动明显增高,强降水(>9 mm·d^-1)后日蒸散量显著增加至雨前的28倍,然后逐渐减少,并持续4个晴朗日后恢复至雨前蒸散量.在整个观测年,梭梭人工林蒸散总量为108 mm,占降水总量的98%,土壤水是梭梭人工林蒸散的水源,为主导因子.净辐射、光合有效辐射、空气温度、水汽压饱和差是决定植被用水和大气边界层水传输的气象动力,为显著影响梭梭人工林蒸散的主要因子.利用日蒸散量与环境因子数据建立了蒸散与土壤含水量和小气候因子的多元回归方程,拟合度(R²)高达0.80.     

Incidence of eccentric molt in first‐year Wrentits increases with fledge date

ABSTRACT In some passerines, the extent of preformative molt varies among individuals. Wrentits (Chamaea fasciata) undergo either a complete preformative molt or an eccentric (i.e., incomplete) preformative molt where some juvenile remiges are retained through the first cycle. Factors that influence the incidence and extent of molt are largely unknown. Using a 10‐yr data set from the Palomarin Field Station in central coastal California, we quantified the incidence of eccentric molt and the degree to which variation in the incidence was associated with fledging date and weather. From 1999 to 2009, 159 Wrentits were banded as nestlings and subsequently recaptured. Of these, 21% of first‐year Wrentits underwent eccentric molt. We used logistic regression and an information theoretic approach to compare models with fledging date, weather (annual precipitation and breeding‐season temperature), and a random effect of year as predictors of the incidence of eccentric molt. Our top model included a random intercept term for year and a fixed effect for the effect of fledging date; birds that fledged later in the season were more likely to undergo eccentric molt. Although the proportion of individuals that underwent eccentric molt varied among years, models with breeding‐season temperature and annual rainfall showed little to no support. Our results suggest that the incidence of eccentric molt is more strongly associated with fledging date than with annual variation in weather. The absence of a correlation with weather suggests that weather does not impose an energetic constraint on molt or, if it does, that birds are constrained in their ability to respond to changes in weather by adjusting the extent of their preformative molt. Other factors, such as nestling condition, may provide alternative explanations for year‐to‐year variability in the incidence of eccentric molt.     

The effect of temperature, relative humidity and rainfall on airborne ragweed pollen concentrations

Major weather parameters have long been known to alter airborne pollen and spore concentrations. The following study was conducted to study the effect of three of these parameters on airborne ragweed pollen concentrations.During the ragweed (RW) season for the years 1997 and 1998, 10 minute pollen collections were taken at least every 4 hours using an Allergenco MK-3 spore trap. Slides were fixed, and counted microscopically at 400X. During this same period, weather parameters were monitored by an Automated Weather Systems recording station located within a few meters of the collector.The ragweed season for this region begins in mid August and ends by mid October. Temperature patterns for the period demonstrated usual daily fluctuations with highs 13 to 35 °C and lows 8 to 24 °C. Relative humidity readings for the period varied between 25 and 100%. Highest RW values were seen after seasonal cooling in September. Daily rainfall for the period varied between 0 and 100 mm. Airborne RW always declined sharply after strong rainfall events (> 10 mm/day). Peak airborne RW concentrations were often associated with the passing of frontal boundaries and the change in wind direction and velocity that accompanies that passing.Factors influencing airborne RW concentrations are multiple and complex, but atmospheric forces have great influence. The passing of major weather fronts and the associated temperature drops, wind disturbances and rainfall are the major factors.     

What affects mRNA levels in leaves of field-grown aspen? A study of developmental and environmental influences

We have analyzed the abundance of mRNAs expressed from 11 nuclear genes in leaves of a free-growing aspen (Populus tremula) tree throughout the growing season. We used multivariate statistics to determine the influence of environmental factors (i.e. the weather before sampling) and developmental responses to seasonal changes at the mRNA level for each of these genes. The gene encoding a germin-like protein was only expressed early in the season, whereas the other tested genes were expressed throughout the season and showed mRNA variations on a day-to-day basis. For six of the genes, reliable models were found that described the mRNA level as a function of weather, but the leaf age was also important for all genes except one encoding an early light-inducible protein (which appeared to be regulated purely by environmental factors under these conditions). The results confirmed the importance of several environmental factors previously shown to regulate the genes, but we also detected a number of less obvious factors (such as the variation in weather parameters and the weather of the previous day) that correlated with the mRNA levels of individual genes. The study shows the power of multivariate statistical methods in analyzing gene regulation under field conditions.     

Seasonality of Fire Weather Strongly Influences Fire Regimes in South Florida Savanna-Grassland Landscapes

Fire seasonality, an important characteristic of fire regimes, commonly is delineated using seasons based on single weather variables (rainfall or temperature). We used nonparametric cluster analyses of a 17-year (1993–2009) data set of weather variables that influence likelihoods and spread of fires (relative humidity, air temperature, solar radiation, wind speed, soil moisture) to explore seasonality of fire in pine savanna-grassland landscapes at the Avon Park Air Force Range in southern Florida. A four-variable, three-season model explained more variation within fire weather variables than models with more seasons. The three-season model also delineated intra-annual timing of fire more accurately than a conventional rainfall-based two-season model. Two seasons coincided roughly with dry and wet seasons based on rainfall. The third season, which we labeled the fire season, occurred between dry and wet seasons and was characterized by fire-promoting conditions present annually: drought, intense solar radiation, low humidity, and warm air temperatures. Fine fuels consisting of variable combinations of pyrogenic pine needles, abundant C4 grasses, and flammable shrubs, coupled with low soil moisture, and lightning ignitions early in the fire season facilitate natural landscape-scale wildfires that burn uplands and across wetlands. We related our three season model to fires with different ignition sources (lightning, military missions, and prescribed fires) over a 13-year period with fire records (1997–2009). Largest wildfires originate from lightning and military ignitions that occur within the early fire season substantially prior to the peak of lightning strikes in the wet season. Prescribed ignitions, in contrast, largely occur outside the fire season. Our delineation of a pronounced fire season provides insight into the extent to which different human-derived fire regimes mimic lightning fire regimes. Delineation of a fire season associated with timing of natural lightning ignitions should be useful as a basis for ecological fire management of humid savanna-grassland landscapes worldwide.     

Nitrogen and yield potential of irrigated rice

Yield potential of modern rice varieties and implications for N management were evaluated in a series of field studies that provided data for validation of an eco-physiological simulation model for rice. We tested the hypothesis that N was the major factor limiting yield potential of irrigated rice. The simulation model ORYZA1 was used to evaluate the observed yield differences between varieties grown with different N management and in different environments. The model explained differences in yield of the treatments resonably well on the basis of differences in radiation, temperature, leaf N content and variety coefficients for phenological development. It was demonstrated by the model and experimental data that yield levels of 6 t ha^-1 in the wet season and 10 t ha^-1 in the dry season can be obtained in the tropics with the current short duration varieties only when the N supply from soil and fertilizer is adequately maintained at key growth stages. Yield probabilities for rice crops were simulated for different environments using long term weather data at two Philippine sites.     

Global evaluation of a semiempirical model for yield anomalies and application to within‐season yield forecasting

Quantifying the influence of weather on yield variability is decisive for agricultural management under current and future climate anomalies. We extended an existing semiempirical modeling scheme that allows for such quantification. Yield anomalies, measured as interannual differences, were modeled for maize, soybeans, and wheat in the United States and 32 other main producer countries. We used two yield data sets, one derived from reported yields and the other from a global yield data set deduced from remote sensing. We assessed the capacity of the model to forecast yields within the growing season. In the United States, our model can explain at least two‐thirds (63%–81%) of observed yield anomalies. Its out‐of‐sample performance (34%–55%) suggests a robust yield projection capacity when applied to unknown weather. Out‐of‐sample performance is lower when using remote sensing‐derived yield data. The share of weather‐driven yield fluctuation varies spatially, and estimated coefficients agree with expectations. Globally, the explained variance in yield anomalies based on the remote sensing data set is similar to the United States (71%–84%). But the out‐of‐sample performance is lower (15%–42%). The performance discrepancy is likely due to shortcomings of the remote sensing yield data as it diminishes when using reported yield anomalies instead. Our model allows for robust forecasting of yields up to 2 months before harvest for several main producer countries. An additional experiment suggests moderate yield losses under mean warming, assuming no major changes in temperature extremes. We conclude that our model can detect weather influences on yield anomalies and project yields with unknown weather. It requires only monthly input data and has a low computational demand. Its within‐season yield forecasting capacity provides a basis for practical applications like local adaptation planning. Our study underlines high‐quality yield monitoring and statistics as critical prerequisites to guide adaptation under climate change.     

The regulation of activity in populations of the terrestrial slugLimax maximus (Gastropoda; Limacidae)

The activity of the slug Limax maximus was studied in relation to weather. Three hundred-and-fifty-eight hourly observations of activity and weather were made on 21 nights from May until October, 1976. Factors causally important to molluscan activity were included in a step-down correlation-regression analysis of daily and seasonal behavior. The analysis was also performed using weather data from the previous hourly observation. Models using lag-weather did not explain as much variability as did concurrent weather. The regression models explained about 73% to 87% of the observed variation in activity. The most important factors included in the regression models were time of day (circadian rhythm), light intensity, changes in light intensity and surface temperature. Shelter temperature, temperature gradients, length of the night, and time of sunset were also included in some models. Age and hydration were shown to be key factors in other experiments. A model incorporating weather thresholds estimated from field data explained 83.06% of the variability in the activity of L. maximus over the season. The values predicted from the model did not differ significantly from those actually observed in the field (Kolmogorov-Smirnov test, p>0.50).     

Factors affecting chick growth in the South Polar Skua (Catharacta maccormicki): food supply, weather and hatching date

This study investigated chick growth in a pelagic Antarctic seabird, the South Polar Skua (Catharacta maccormicki). The factors food supply, weather and hatching date were analysed in a population of 54 breeding pairs at King George Island/South Shetland Islands. Food supply was manipulated by offering fish corresponding to 20% of daily energy demand of chicks to half of the breeding pairs every second day. Growth of mass, head, wing and tarsus was followed and related to the treatment, weather conditions, hatching date and interactive effects. Food supply did not limit chick growth in the studied season. Parents seemed to try to feed their chicks at a maximum rate and succeeded in the studied season because the general food supply was very good. Low temperatures and strong winds depressed chick growth. A growth advantage of food-supplemented chicks could be observed when the natural conditions for chick growth were sub-optimal. Chick growth rate was strongly negatively associated with hatching date and worsening weather during the reproductive season could be excluded as explanatory variable for this finding.     

Weather Influences Multiple Components of Greater Prairie-Chicken Reproduction

The influence of weather on wildlife populations has been documented for many species; however, much of the current literature has focused on the effects of weather within a season and consists of short-term studies. The use of long-term datasets that cover a variety of environmental conditions will be essential for assessing possible carry-over effects of weather experienced in one season on behavior and fitness in subsequent seasons. In this study, we evaluated the effects of weather variables measured over multiple temporal scales on the reproductive performance and behavior of greater prairie-chickens (Tympanuchus cupido) in Osage County, Oklahoma, USA, from 2011–2019. Considering weather over a range of temporal extents allowed us to determine the relative importance of short-term weather events, such as daily temperature and precipitation, versus more chronic shifts in weather such as persistent drought on the reproductive performance of greater prairie-chickens. We used an information-theoretic model building approach to develop models describing the effects of daily weather variables and drought conditions on daily nest survival, nest incubation start dates, and clutch size. Daily nest survival was primarily influenced by conditions experienced during incubation with daily nest success declining in years with wetter than average springs and during extreme precipitation events. Daily nest survival also declined under higher maximum daily temperatures, especially in years with below-average rainfall. Greater prairie-chickens began nesting earlier and had smaller clutch sizes for initial nests and renests in years with warmer temperatures prior to the nesting season. Additionally, incubation of nests started later in drought years, indicating carry-over effects in greater prairie-chicken reproductive behaviors. Our work shows that if the weather in the Great Plains becomes more variable, with increasing frequency of drought and extreme precipitation events, wildlife species that inhabit these grassland landscapes will likely experience changes in reproduction, potentially influencing future populations. © 2020 The Wildlife Society.     

干旱荒漠区沙冬青茎干液流变化特征及其与气象因子的关系

采用热平衡包裹式树干液流仪(stem heat balance,SHB)监测沙冬青(Ammopiptanthus mongolicus)茎干液流日变化,并利用自动气象站同步监测太阳辐射、空气温度、空气相对湿度、风速等气象因子日变化,研究沙冬青茎干液流在不同季节和天气条件下的日变化特征及其与环境气象因子的关系.研究表明:(1)在夏季沙冬青茎干液流昼夜区别明显,且变幅较大,液流于8:00~9:00开始启动,并迅速于9:00左右达到峰值,然后立即有一个大幅度的下降,后在小幅度波动中维持到19:00左右停止;沙冬青茎干液流在夜间较弱;(2)不同天气条件对沙冬青液流的变化影响较大,沙冬青茎干液流速率的总体变化幅度表现为晴天>阴天>沙尘天气;(3)各季节典型天气下沙冬青茎干液流速率表现为夏季>春季>冬季;生长季茎干液流启动时间早,液流量大;春季液流启动时间次之,液流量变化平缓,维持时间长;冬季液流启动时间最迟,液流变化速率大且维持时间短;(4)沙冬青茎干液流与气象因子的关系密切,其中与太阳辐射的关系最为密切,其次是空气温度和相对湿度,影响最小的是风速.     

Reindeer movement patterns in alpine summer ranges

To evaluate the movement rates of semi-domesticated reindeer (Rangifer tarandus tarandus) during the bare-ground season, we used successive GPS positions from 48 female reindeer. Data were collected during the summers of 2002 and 2003 in two Sámi reindeer herding districts in the Swedish mountains, Handölsdalen, and Sirges. The movement rates were analysed at five different time periods: over the whole season, and over the sub-seasons spring, and early summer, mid summer and early autumn. Variation in movements were analysed in relation to vegetation type, altitude, terrain ruggedness, temperature, wind speed, and proximity to hiking trails. We hypothesised that the foraging quality and different weather conditions is an important factor in determining movement rates. We found that reindeer movement rates were similar between study areas and were dependent on vegetation type and on weather conditions. Studying the circadian movements, in mid summer period when daytime oestrid activity are expected to be high, the reindeer stayed at higher altitudes where food quality was low, but moved to low altitudes at night where the food quality was higher. Therefore, we suggest that oestrid activity forces the reindeer to stay in low-quality vegetation types. Reindeer movements were linked to disturbance in areas of intermediate human activity. We found that in Handölsdalen, where hikers are abundant, the movement rates of reindeer decreased closer to the trails whereas in Sirges, where hikers are less abundant, the movement rates of reindeer increased closer to the trails.     

A distributed delay routine-based simulation model of Beauveria bassiana conidial stability in response to environmental stressors

Using published data and equations on therelationship between spore longevity of theentomopathogenic hyphomycetes, Metarhiziumanisopliae var. acridum and Beauveria bassiana (Balsamo) Vuillemin(Deuteromycota: Hyphomycetes) and temperatureand moisture content, a model of sporeviability was constructed based on adistributed-delay routine. The model ismodified via average spore survival time or byincluding an additional attrition (mortality)rate. The model was parameterized usingpublished values from studies on M. a.var. acridum spores, and output comparedfavorably with germination data and with apreviously-developed model. After initializingthe model using parameter estimates of B.bassiana spores from the laboratory andpublished data on changes in (1) spore viabilitywith respect to temperature and moisturecontent, and (2) spore moisture content withrespect to temperature and relative humidity,the model was run using daily min/maxtemperature and relative humidity data andcompared with data from four field experimentsof Mycotech B. bassiana isolate GHAsprayed on canteloupe plants. For two of theexperiments, observed viability trends werecompared to model outputs using weather datafrom both a weather station and fromwithin-canopy temperature and humidity probes. Output using weather station data fitobservations much better than output usingwithin-canopy probe data. For the tworemaining sets of field data, both earlier inthe season, only weather station data wereavailable and the resulting output fitobservations poorly. An attrition rate of 98%was needed to fit output to field data early inthe growing season, and a rate of 74% wasneeded for data collected four weeks later. These attrition rates can be consideredestimates for the proportion of spores dyingfor reasons other than temperature and relativehumidity, and they were attributed largely toUVB radiation due to the more open canopyearlier in the season.     

Tracking gastrointestinal nematode risk on cattle farms through pasture contamination mapping

Gastrointestinal nematode (GIN) parasites in grazing cattle are a major cause of production loss and their control is increasingly difficult due to anthelmintic resistance and climate change. Rotational grazing can support control and decrease reliance on chemical intervention, but is often complex due to the need to track grazing periods and infection levels, and the effect of weather on larval availability. In this paper, a simulation model was developed to predict the availability of infective larvae of the bovine GIN, Ostertagia ostertagi, at the level of individual pastures. The model was applied within a complex rotational grazing system and successfully reproduced observed variation in larval density between fields and over time. Four groups of cattle in their second grazing season (n = 44) were followed throughout the temperate grazing season with regular assessment of GIN faecal egg counts, which were dominated by O. ostertagi, animal weight and recording of field rotations. Each group of cattle was rotationally grazed on six group-specific fields throughout the 2019 grazing season. Maps and calendars were produced to illustrate the change in pasture infectivity (density of L3 on herbage) across the 24 separate grazing fields. Simulations predicted differences in pasture contamination levels in relation to the timing of grazing and the return period. A proportion of L3 was predicted to persist on herbage over winter, declining to similar intensities across fields before the start of the following grazing season, irrespective of contamination levels in the previous year. Model predictions showed good agreement with pasture larval counts. The model also simulated differences in seasonal pasture infectivity under rotational grazing in systems that differed in temperature and rainfall profiles. Further application could support individual farm decisions on evasive grazing and refugia management, and improved regional evaluation of optimal grazing strategies for parasite control. The integration of weather and livestock movement is inherent to the model, and facilitates consideration of climate change adaptation through improved disease control.     

Ecological implications of projected climate change scenarios in forest ecosystems in northern Michigan,USA

Changes in seasonal temperature and precipitation, as predicted by several global climate models, were utilized together with a stochastic daily weather stimulation model to evaluate the ecological impacts of projected global climate change scenarios on temperate forest ecosystems in northern Michigan, USA. The model simulated the impacts of these projected changes on ecologically significant weather variables, such as the length of the frost-free period, average growing season temperature, average growing season degree days (4.4° C basis), summer precipitation, potential evaporation during the growing season, and the ratio of precipitation to potential evaporation during July and August. The results indicate that even the lower range of predicted climate changes could lead to ecologically and commercially significant changes in the composition and productivity of these forests. Of particular concern is the possibility of climatically induced regional decline episodes for a number of important commercial species in the northern temperate forests of central North America.     

The Impact of Nature Experience on Willingness to Support Conservation

We hypothesized that willingness to financially support conservation depends on one''s experience with nature. In order to test this hypothesis, we used a novel time-lagged correlation analysis to look at times series data concerning nature participation, and evaluate its relationship with future conservation support (measured as contributions to conservation NGOs). Our results suggest that the type and timing of nature experience may determine future conservation investment. Time spent hiking or backpacking is correlated with increased conservation contributions 11–12 years later. On the other hand, contributions are negatively correlated with past time spent on activities such as public lands visitation or fishing. Our results suggest that each hiker or backpacker translates to $200–$300 annually in future NGO contributions. We project that the recent decline in popularity of hiking and backpacking will negatively impact conservation NGO contributions from approximately 2010–2011 through at least 2018.     

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.