Developmental times and age-specific life tables for Lygus lineolaris (Heteroptera: Miridae), reared at multiple constant temperatures

Developmental times and survivorship of tarnished plant bug nymphs, Lygus lineolaris (Palisot de Beauvois), and longevity and reproduction of adult tarnished plant bug adults reared on green beans were studied at multiple constant temperatures. The developmental time for each life stage and the total time from egg to adult decreased with increasing temperature. Eggs required the longest time to develop followed by fifth instars and then first-instars. Total developmental time from egg to adult was shortest at 32°C, requiring 18.0 ± 0.3 d and 416.7 ± 31.3 DD above 7.9°C, the estimated minimum temperature for development from egg to adult. Sex did not affect total developmental times and did not affect median survival time. Adults lived significantly fewer days at high temperatures (30-32°C: 17-19 d) compared with temperatures below 30°C (range: 24.5-39.4 d) and the number of eggs laid per day increased from ≈ 4 at 18°C to a maximum of 9.5 eggs per day at 30°C. Total egg production over the lifetime of female tarnished plant bugs increased with temperature reaching a maximum of 175 eggs on average at 27°C, total egg production declined at temperatures above 27°C (30°C: 110.8, 32°C: 77.3 eggs per female). The highest net reproductive rate 74.5 (R(0)) was obtained from insects maintained at 27°C. The intrinsic rate of natural increase (r(m)) increased linearly with temperature to a maximum value of 0.1852 at 30°C, and then decreased at 32°C. Generation and doubling times of the population were shortest at 30°C, 21.0 and 3.7 d, respectively.     

Effects of temperature shifts on growth rate and lipid characteristics of Synechocystis sp. PCC6803 in a bench-top photobioreactor

Synechocystis sp. PCC6803 exhibited a high degree of variation in biomass and lipid production rates in response to temperature changes in a photobioreactor. Compared with an optimal temperature of 30-33°C, a higher temperature of 44°C and lower temperatures of 22°C and 18°C severely inhibited the specific growth rate (up to a 66% decrease), biomass production rate (up to a 71% decrease), nutrient utilization rates (up to a 77% decrease), and lipid production rate (up to a 80% decrease). Temperature stress triggered changes in the relative percentage of individual fatty acids (mainly for C16:0 and C18:3), and degree of unsaturation significantly changed: 0.87 at 30°C, 0.62 at 44°C, and 1.29 at 18°C. Although PCC6803 survived temperature stress and maintained its predominate position in the culture, it could not fully recover from long-term temperature stress. Thus, avoiding prolonged exposure to extreme temperature is crucial for using PCC6803 as feedstock for biofuel production.     

Survival, development and food energy partitioning of nase larvae and early juveniles at different temperatures

Survival was generally high, 94–100%, for newly hatched larvae of the nase Chondrostoma nasus held at 10, 13, 16, 19, 22, 25 and 28° C up to day 66 post-fertilization. The developmental rate decreased with age and increased with temperature. Specific growth rates increased with temperature; within one temperature range growth rate decreased with ontogenetic development. Food consumption and respiration increased with temperature and body size. A temperature increase from 25 to 28° C resulted in slightly reduced survival, minor acceleration of developmental growth and respiration rates, and impeded skeleton formation. Growth efficiency of consumed energy decreased throughout the larval period from 55 to 67% at the first larval stage (L1) to 36–48% at the first juvenile stage (J₁). A similar trend for assimilation efficiency and its utilization for growth was observed. The constant temperatures required by larval nase ranged from a minimum 8–10° C to a maximum 25–28° C. A shift of optimum temperatures, 8–12, 13–16, 15–18, 19 and 22° C for nase spawning, embryonic development, yolk feeding larvae, early externally feeding larvae and, late larvae and juveniles, respectively, paralleled the spring rise in the river water temperature. Larval and juvenile nase show high survival, growth and energy conversion efficiencies compared with other fish species. On the other hand, low survival rates and growth can be attributed to external perturbations; thus, young nase may be considered a good indicator of the environmental and ecological integrity of river systems.     

The Biology and Thermal Requirements of the Fennel Aphid Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae)

The relationship between the insect development rate and temperature was established very early and represents an important ecological variable for modeling the population dynamics of insects. The accurate determination of thermal constant values and the lower and upper developmental thresholds of Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae) on fennel (Foeniculum vulgare Miller (Apiales: Apiaceae)) crops would obviously benefit the effective application of control measures. This paper is a study of the biology and thermal requirements of H. foeniculi. Winged insects were collected from fennel crops at the Embrapa Algodão in Campina Grande, Paraíba. Nymphs (age ≤24 h) produced by winged insects were subjected to constant temperatures of 15, 20, 25, 28, 30 or 33°C, a photophase of 12 h and a relative humidity of 70±10%. The results of the study showed that at temperatures between 15 and 30°C, H. foeniculi nymphs were able to develop normally. The four instars were found at all temperatures tested. However, temperatures of 3 and 33°C were lethal to the nymphs. The nymph stage development time varied from 5 (30°C) to 19 (15°C) days. The influence of temperature on the development time is dependent on the instar. The base temperature (Tb) and the thermal constant (K) for the nymph stage were estimated at 11.2°C and 107.5 degree-days, respectively. The shortest nymph development stage was observed at 30°C, and the highest nymph viability (85.0%) was observed at 28°C. This information can be used for developing phenological models based on the temperature and development rate relationships so that outbreaks of H. foeniculi in the fennel crop can be predicted, therefore improving the application of control programs targeting this fennel pest.     

The effect of temperature on the behaviour and development of Triatoma brasiliensis

Abstract. The effects of temperature on the development of early stages and the thermopreference of nymphs and adults were analysed in the haematophagous bug Triatoma brasiliensis Neiva, 1911 (Hemiptera, Reduviidae). Egg hatching, mortality of nymphs, feeding and moulting success of the early stages of T. brasiliensis were all affected by temperature. While high rates of egg hatching were observed between 25 and 27 °C, no hatching occurred at 12, 19 and 38 °C. The mortality of first‐instar nymphs was highest at 38 °C, at which no insects survived after 10 days of exposure. Feeding success was only affected at the lowest temperature (12 °C). No ecdysis was observed in the groups exposed to 12, 19 and 21 °C. Recently fed fourth‐instar nymphs preferred to stay at a temperature of approximately 30 °C. The preferred temperature began to decline gradually to approximately 27 °C during ecdysis, reaching 26 °C at 30 days after ecdysis. After a second blood meal, the insects' preferred temperature was again approximately 30 °C. The thermopreference pattern of females was similar to that of nymphs. Nymphs and females showed a daily fluctuation in their preferred temperature, moving towards higher values at the beginning of the dark phase, and choosing lower ones after this time interval, at which they remained until the end of the light phase. The females laid their eggs in all sectors of the arena, although the largest numbers of eggs were found between 28 and 32 °C.     

Sex and proximity to reproductive maturity influence the survival, final maturation, and blood physiology of Pacific salmon when exposed to high temperature during a simulated migration

Some Pacific salmon populations have been experiencing increasingly warmer river temperatures during their once-in-a-lifetime spawning migration, which has been associated with en route and prespawn mortality. The mechanisms underlying such temperature-mediated mortality are poorly understood. Wild adult pink (Oncorhynchus gorbuscha) and sockeye (Oncorhynchus nerka) salmon were used in this study. The objectives were to investigate the effects of elevated water temperature on mortality, final maturation, and blood properties under controlled conditions that simulated a "cool" (13°C) and "warm" (19°C) freshwater spawning migration. After 10 d at 13°C, observed mortality was 50%-80% in all groups, which suggested that there was likely some mortality associated with handling and confinement. Observed mortality after 10 d at 19°C was higher, reaching ≥98% in male pink salmon and female pink and sockeye salmon. Thus, male sockeye salmon were the most thermally tolerant (54% observed mortality). Model selection supported the temperature- and sex-specific mortality patterns. The pink salmon were closer to reproductive maturation and farther along the senescence trajectory than sockeye salmon, which likely influenced their survival and physiological responses throughout the experiment. Females of both species held at 19°C had reduced plasma sex steroids compared with those held at 13°C, and female pink salmon were less likely to become fully mature at 19° than at 13°C. Male and female sockeye salmon held at 19°C had higher plasma chloride and osmolality than those held at 13°C, indicative of a thermally related stress response. These findings suggest that sex differences and proximity to reproductive maturity must be considered when predicting thermal tolerance and the magnitude of en route and prespawn mortality for Pacific salmon.     

Effects of temperature on Anoplophora glabripennis (Coleoptera: Cerambycidae) larvae and pupae

Developmental thresholds, degree-days for development, larval weights, and head capsule widths for each larval instar and the pupal stage of Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae) were studied at eight constant temperatures (5, 10, 15, 20, 25, 30, 35, and 40°C) for two source populations (Ravenswood, Chicago, IL [IL], and Bayside, Queens, NY [NY]). The estimated lower threshold temperature for development of instars 1-5 and the pupal stage was near 10°C and was near 12°C for the higher instars. Developmental rate was less temperature sensitive for instars 5-9 compared with instars 1-4. Development for all but the first instar was inhibited at constant temperatures >30°C, and all instars failed to develop at 40°C. Although the two source populations had similar responses to temperature, IL larvae were heavier than those from NY. Temperature and its influence on larval weight had profound impacts on whether a larva proceeded to pupation. Based on the temperature effects detailed here, larval development and pupation should be possible in most of the continental United States where suitable hosts are available. These data can be used to develop a degree-day model to estimate beetle phenology; however, at least 2°C should be added to air temperatures to adjust for the mediation of temperature by the wood. These data provide a basis for predicting the potential geographical range of this species and for developing phenological models to predict the timing of immature stages, both of which are important for management programs.     

Intrinsic optimum temperature of the diamondback moth and its ecological meaning

Temperature can notably affect development rate and intrinsic rate of increase of the diamondback moth, Plutella xylostella L. The intrinsic rate of increase is usually regarded as a good measure of fitness in insects, and the constant temperature at which the intrinsic rate of increase reaches its maximum is defined as the "optimal" temperature for an insect species to survive. The estimates of optimal temperature for some insects and mites are ~30°C. However, the Sharpe-Schoolfield-Ikemoto model provides an estimate about the intrinsic optimum temperature at which the probability of an enzyme being in the active state is maximal. The intrinsic optimum temperature is considered to be the most suitable temperature for an insect species to survive. The estimates of intrinsic optimum temperature for some insects and mites are ~20°C. The optimal temperature and the intrinsic optimum temperature of the diamondback moth were estimated in the current study. The former estimate is 28.4 (95% CI: 26.2-28.8°C), whereas the latter estimate is 19.4°C (95% CI: 17.9-20.5°C). Considering the daily average air temperatures during the peaks of the diamondback moth in China, the intrinsic optimum temperature of 19.4°C might represent the most suitable temperature for this insect to survive. We also discussed whether it is sounded to use the intrinsic rate of increase as the fitness. Because the intrinsic rate of increase cannot reflect the density-dependence of population and the trade-off between individual body mass and population size, it is inappropriate to equate these two concepts.     

Effects of temperature and food level on growth and development of a planktonic water mite

We analysed the relative effects of food availability and temperature on rates of growth and development of a predatory planktonic water mite, Piona exigua. Growth in length of mites fed Daphnia, Ceriodaphnia and Chydorus was analysed by Gompertz or von Bertalanffy curves; these curves were compared by parallel curve analysis. Growth rates of nymphs and adult female mites increased with temperature; the duration of the imagochrysalis stage decreased. Females grown at 10 °C were smaller at final size than females grown at 15 °C, 18 °C or 22 °C. Females reared at food levels of 15 or 30 prey l⁻¹ grew more slowly and were smaller than those provided with 60 or 120 prey l⁻¹. Nymphs grew more slowly when Daphnia were the only prey, than when smaller prey were available. Food level did not affect nymph growth at 10 °C or 15 °C, but growth at 18 °C or 22 °C may have been slowed at the lowest food levels. Synergistic effects of temperature and food level on nymph growth were apparent only from analysis of growth curves and not from stage duration data.     

Temperature and diet effects on immature development of predatory mite Typhlodromus athenas Swirski and Ragusa (Acari: Phyotseiidae)

Temperature and food quality both can influence growth rates and developmental time of herbivorous insects and mites. Typhlodromus athenas Swirski and Ragusa is an indigenous mite in the Mediterranean region and data on its temperature dependent development are lacking. In the current study, temperature-dependent development and survival of T. athenas immature stages were evaluated on eggs and all stages of Tetranychus urticae Koch, as well as on almond (Prunus amygdalis Batsch) pollen, under seven constant temperatures ranging from 15 to 35°C, 65% RH, and a photoperiod of 16:8 (L:D) h. On both diets survival was considerably high at all temperatures. The longest developmental period of immature stages was recorded at 15°C, whereas the shortest was at 30°C. Female immatures on almond pollen had shorter developmental time compared to that on twospotted spider mites. Food had a significant effect on female total developmental time at temperatures lower than 25°C. The lower developmental thresholds, estimated by a linear model, for egg-to-adult of females and males fed on pollen were 8.60 and 8.77°C, respectively, whereas on T. urticae they were 10.15 and 10.62°C, respectively. Higher values of tmin for total development were estimated by a nonlinear model (Lactin-2), and ranged from 10.21°C for both females and males on almond, to 11.07 for females and 10.78°C for males on prey. Moreover, this model estimated optimal and lethal temperatures accurately. The results of this study indicate that T. athenas appears better adapted to higher temperatures that occur in the Mediterranean region and may be a useful biological control agent.     

Thermal requirements for the development and reproduction of Nysius huttoni White (Heteroptera: Lygaeidae)

Nysius huttoni White is an economically important pest of wheat and brassica crops in New Zealand. Because of its frequent presence in export fruit packages, it is also considered an important quarantine pest to countries that trade with New Zealand. To provide critical information for the pest risk analysis, forecast and management of N. huttoni, we investigated the effect of five consistent temperatures (10, 15, 20, 25, and 30 degrees C) on its development, survival and reproduction. At 10 degrees C both eggs and nymphs did not develop but the latter grew. Nymphs could survive 10 degrees C for >1.5 mo, with the fifth instar nymphs surviving for up to 145 d. Adults could live for at least 100 d at this temperature. This species could not complete its lifecycle at or below 15 degrees C. Between 15 and 30 degrees C, fifth instar stage was significantly longer than other nymphal stages. Egg hatch rate and total survival rate for all stages were significantly higher at 20 degrees C than at other test temperatures. The developmental rate of different life stages increased linearly with the increase of temperatures from 15 to 30 degrees C. The estimated low temperature threshold for the completion of lifecycle was 11.9 degrees C, and that for mating and oviposition was 12.3 and 16.8 degrees C, respectively. The thermal requirement for completing a life cycle of N. huttoni was 625 DD. The time needed for completing a life cycle was similar for both sexes. Temperature had little effect on adult body weight and sex ratio. Implications of the above findings are discussed.     

Effect of temperature and sex on growth patterns in nymphs of the mayfly Hexagenia hilineata in the laboratory

SUMMARY. Eggs collected from Hexagenia bilineata females were successfully reared in the laboratory at temperatures of 15, 20, 25 and 30°C. Eggs did not hatch at 10°C and although hatching was successful at 35°C, all nymphs at this temperature died while in early instars.
Survival of nymphs between the approximate size interval of 4–14 mm showed a significant decrease with increased temperatures. Nymphs at 15°C, however, generally did not survive transformation to the subaduit stage.
The growth pattern of individual nymphs was well described by a logistic curve at most temperatures. Furthermore, growth pattern was significantly affected by both temperature and sex.
Rate of development from oviposition to first emergence increased with increasing temperatures in a linear fashion between 15 and 30°C. The relationship was equally well described by a hyperbolic equation and a power-law equation. By extrapolation from the hyperbolic equation, the lower threshold temperature for development was estimated to be 10.1°C3.1°C. The degree (°C)-days required for development from oviposition to first emergence was calculated to be 2337 days with 95% confidence limits of 2045–2727 days under laboratory conditions.     

温度对胡萝卜微管蚜生长发育繁殖的影响

【目标】明确温度对胡萝卜微管蚜Semiaphis heraclei(Takahashi)生长发育和繁殖的影响。【方法】在室内5个温度梯度下(19、22、25、28、31℃)观察并比较胡萝卜微管蚜的发育历期、存活率、存活寿命及产仔量。【结果】在19?31℃范围内,胡萝卜微管蚜各龄期及完整世代的发育历期均随着温度的升高而缩短,完成一个世代分别需要22.17、17.13、12.57、10.03和7.83 d。温度与发育速率呈极显著相关(P<0.01,r>0.8),温度越高发育速率越快。胡萝卜微管蚜4个若蚜期和世代的发育起点分别为14.15、13.87、13.64、15.06、12.92℃,有效积温分别为29.98、29.30、28.54、24.00和144.21日?度。建立了胡萝卜微管蚜各个发育阶段的历期预测式。在5个恒温下胡萝卜微管蚜1?4龄及世代的存活率随温度的变化而小幅波动。在19?31℃范围内,该蚜虫世代的存活率分别为40.0%、52.5%、62.5%、60.0%和47.5%。25℃该蚜虫的存活率相对较高,1?4龄及世代的存活率分别为82.5%、81.8%、92.6%、100%和62.5%。在相同温度条件下该蚜虫不同发育阶段的存活率存在差异。存活寿命随着温度的升高而缩短,19℃时寿命最长,为33.30 d,31℃时寿命最短,为15.40 d。产仔期随着温度的升高而缩短,19℃时产仔期为11.13 d,31℃时为7.57 d。在19?31℃范围内,该蚜虫的单雌产仔总量分别为26.33、27.93、32.53、27.13和17.93头。【结论】温度是影响胡萝卜微管蚜的生长发育、存活和繁殖的重要因素。25℃时胡萝卜微管蚜各龄期及世代的发育历期较短,存活率较高,单雌产仔总量最大。25℃较适合该蚜虫生长发育和繁殖。     

Effect of temperature on post-wintering development and total lipid content of alfalfa leafcutting bees

Temperature plays an important role in effective management of the alfalfa leafcutting bee [Megachile rotundata (F.); Megachilidae], the major commercial pollinator of seed alfalfa [Medicago sativa (L.); Fabaceae] in North America. To improve our understanding of threshold and optimum rearing temperatures of M. rotundata, we examined the effect of temperature on postwintering development by using a greater number of temperature treatments than applied in previous studies (19 versus eight or fewer) and analytical tools formulated to model nonlinear relationships between temperature and insect development rates. We also tested the hypothesis that rearing temperature influences adult body lipid content at emergence, which could affect adult survival, establishment and performance as a pollinator, and reproductive success. We found that the Lactin-2 and Briere-2 models provided the best fits to data and gave reasonable estimates of lower (16-18°C) and upper (36-39°C) developmental thresholds and optimum (33-34°C) rearing temperatures for maximizing development rate. Bees successfully emerged over a broad range of temperatures (22-35°C), but variation in development rate among individuals reared at the same temperature was lowest at 31-33°C. The optimum rearing temperature to maximize the proportion of body lipids in adults was 27-29°C. Our results are discussed in relation to previous findings and speak to the difficulties in designing practical rearing guidelines that simultaneously maximize development rate, survival, and adult condition, while synchronizing adult emergence with alfalfa bloom.     

Ammonia emissions during vermicomposting of sheep manure

The effect of C:N ratio, temperature and water content on ammonia volatilization during two-phase composting of sheep manure was evaluated. The aerobic phase was conducted under field conditions. This was followed by Phase II, vermicomposting, conducted in the laboratory under controlled conditions of water content (70% and 80%) and temperature (15 and 22 °C). The addition of extra straw lead to a 10% reduction in NH3 volatilization compared to sheep manure composted without extra straw. Temperature and water content significantly effected ammonia volatilization at 0 day in Phase II, with a water content of 70% and temperature of 22 °C leading to greater losses of ammonia. Nitrogen loss by ammonia volatilization during vermicomposting ranged from 8% to 15% of the initial N content. The addition of extra straw did not result in significant differences in total carbon content following vermicomposting.     

短时高温对烟蚜生长发育、繁殖和取食行为的影响

【目的】烟蚜Myzus persicae是一种世界性的重要农业害虫,本研究测定了短时高温对烟蚜生长发育、繁殖和取食行为的影响。【方法】测定初产若蚜每天在30, 35和40℃下处理1, 2和4 h的发育历期及成蚜在相同处理下的繁殖力,应用刺吸电位技术（electronic penetration graph, EPG）测定成蚜在30和35℃下处理1和2 h后以及在25, 28, 30和35℃恒温下的取食行为。【结果】短时高温（30~35℃）对各龄若蚜发育历期影响较小,但40℃下处理2 h后其发育历期显著增加（P<0.05）;若蚜存活率、成蚜寿命及其繁殖历期随温度和处理时间的增加而降低;在25~35℃下,随温度和处理时间的增加,成蚜繁殖率变化较小,但40℃下处理2和4 h后,其繁殖率显著降低（P< 0.01）;短时高温对烟蚜的取食行为影响显著,随温度和处理时间的增加,非刺探波np数量（P<0.05）及其持续时间（P<0.01）显著减少,而韧皮部刺吸波E持续时间显著增加（P<0.05）;但持续高温下,随温度升高,np波数量及其持续时间先减少后增加,而E波则相反。【结论】短时高温对烟蚜若蚜发育速率影响较小,但使若蚜存活率、成蚜寿命及其繁殖历期显著降低,且对成蚜繁殖有一定的抑制作用,而对成蚜的取食有一定的促进作用。研究结果有助于了解烟蚜不同年份间夏季种群数量的变化机制。     

Temperature and Photoperiodic Control of Development in the Green Shield Bug Palomena prasina (L.) (Heteroptera,Pentatomidae) in Leningrad Province

Thermal reaction norms for development (the lower temperature threshold, temperature sensitivity, and sum of degree-days) can show phenotypic plasticity in response to a combination of ecological factors. The goal of this study was to evaluate the degree of plasticity of the thermal reaction norms for development under different photoperiodic conditions in the green shield bug Palomena prasina. Experiments were conducted in 2015 and 2016. In 2015, two photoperiodic regimens (12 and 22 h of light per day) and five constant temperatures (20, 22, 24, 26, and 28°C) were used; a lower temperature of 16°C was added in 2016. There were no differences in the egg developmental time between the two photoperiodic conditions and across the two experiments. Under the short-day photoperiodic regimen, nymphal development was faster at all the temperatures and was characterized by greater thermal sensitivity and a higher temperature threshold than under the long-day photoperiod. Besides, the relationship between the developmental rate and temperature deviated from linearity at 26 and 28°C under short-day conditions. The adaptive nature of the observed nymphal response to photoperiodic conditions was confirmed by our phenological observations and an outdoor cage experiment. The adult body mass slightly increased with rising temperature under short-day conditions but did not depend on the temperature under long-day ones. Females were larger than males, and both sexes had a greater body mass under long-day conditions than under short-day ones. In 2015, the eggs for experiments were collected before mid-July, almost a month later than in 2016. Nymphs that hatched from the later eggs (in 2015) had significantly higher relative growth rates than the early-season nymphs (in 2016) at 20, 22, and 24°C under both photoperiods. This discrepancy between years was probably related to the maternal effect, namely, the difference in the female physiological age.

     

Ixodes rubicundus nymphs are short-day diapause-induced ticks with thermolabile sensitivity and desiccation resistance

The Karoo Paralysis tick, Ixodes rubicundus Neumann (Acari: Ixodidae), is a semi-voltine ixodid that survives stressful environmental conditions using morphogenetic diapause (eggs and engorged nymphs) and desiccation resistance. Both photoperiod and temperature influence diapause induction in the engorged nymph. Ixodes rubicundus nymphs are typical long-day photoperiodic organisms. The critical photoperiod is approximately 13.5 h light, 10.5 h dark, and they display a thermolabile response. The period between detachment and apolysis in engorged nymphs is modified by photoperiod; however, apolysis to ecdysis is not affected by photoperiod. Thus, initiation of development, but not the actual process is controlled by photoperiod. Most engorged nymphs delayed metamorphosis when exposed to short-day regimen (LD 12 : 12 h) after feeding. Nymphs exposed to pre- and post-feeding long-day regimen (LD 14 : 10 h) developed. Times for 50% of nymphs to apolyse when exposed to photoperiods of LD 14 : 10 h, 13.5 : 10.5 h, 13 : 11 h and 12 : 12 h were 28, 36, 40 and 58 days, respectively. Times for 50% of engorged nymphs to ecdyse ranged from 38 to 40 days after apolysis. Nymphs were sensitive to photoperiodic exposures before, during and after feeding. Nymphs exposed to long day (LD 14 :10 h) before and during feeding, moulted at 20 degrees C; however, most exposed to 10 degrees C followed by 20 degrees C (post-feeding) went into diapause. Both short- (10 : 14 h) and long- (14 : 10 h) day exposed engorged nymphs survived 45 days at 0% r.h. (n = 73), but diapause-destined ticks kept at 13 degrees C lost the least mass (29.5+/-9.5%, SD), while nondiapause ticks at 23 degrees C lost the most (48.7+/-8.2%, SD). Termination of diapause and transition to development probably coincides with a definite increase of water vapour uptake by engorged nymphs. Comparatively, I. rubicundus engorged nymphs are more desiccation tolerant than a North-American counterpart, Amblyomma cajennense (Fabricius) (Acari: Ixodidae), which is also semi-arid- to xeric-adapted. Diapause conveys important survival attributes that enable engorged I. rubicundus nymphs to inhabit a semi-arid environment with great temperature extremes, and to synchronize their activity periods with seasons and host utilization patterns.