Temperature influences the handling efficiency of an aphid parasitoid through body size-mediated effects

It is well known that increasing the ambient temperature increases the metabolic rate and consequently, the foraging rate of most insects. However, temperature experienced during the immature stages of insects affects their adult size (an inverse relationship). Because body size is generally correlated to foraging success, we hypothesized that temperature indirectly influences the foraging efficiency of adult insects through developmental effects. We first investigated the role of parasitoid: host body size ratio on the handling time of Aphidius colemani (Viereck) (Hymenoptera: Braconidae), then tested the prediction that increasing temperature during immature development increases the handling time of adults. As expected, parasitoids took longer to handle large aphids than small aphids. However, large parasitoids did not have shorter handling times than small parasitoids except when attacking large (adult) aphids. Developmental temperature had the predicted effect on parasitoids: Individuals reared at 25°C were smaller than those insects reared at 15°C. Parasitoids reared at 15°C had similar short handling times for both first instar and adult aphids, whereas parasitoids reared at 25°C took longer to handle adult aphids than first instar aphids. The size-mediated effect of temperature through development on parasitoid efficiency was opposite to the more familiar direct effect of temperature through metabolic rate. We conclude that the net effect of temperature on foraging insects will depend on its relative influence on immature and adult stages.     

Developmental database for phenology models: related insect and mite species have similar thermal requirements

Two values of thermal requirements, the lower developmental threshold (LDT), that is, the temperature at which development ceases, and the sum of effective temperatures, that is, day degrees above the LDT control the development of ectotherms and are used in phenology models to predict time at which the development of individual stages of a species will be completed. To assist in the rapid development of phenology models, we merged a previously published database of thermal requirements for insects, gathered by online search in CAB Abstracts, with independently collected data for insects and mites from original studies. The merged database comprises developmental times at various constant temperatures on 1,054 insect and mite species, many of them in several populations, mostly pests and their natural enemies, from all over the world. We show that closely related species share similar thermal requirements and therefore, for a species with unknown thermal requirements, the value of LDT and sum of effective temperatures of its most related species from the database can be used.     

A method for the rapid measurement of thermal tolerance traits in studies of small insects

Abstract A technique for rapidly measuring non‐lethal thermal tolerance traits in small insects and terrestrial arthropods of similar size is described. Single or multiple individuals are heated or cooled in an arena milled into a temperature‐controlled aluminium block and their behaviour recorded continuously using a digital video camera. Data are collected retrospectively by playback of the stored images. To illustrate this technique measurement of six thermal tolerance traits using this method is described using first instar nymphs (body length = 0.66 mm) of the aphid Myzus persicae. These traits are high and low temperatures at which individual aphids cease walking, high and low temperatures at which aphids move for the final time, the temperature at which aphids begin to recover from chill coma, and the temperature at which they begin to walk again. The method is validated by comparing the results of multiple low temperature assays. No significant differences are detected between assays. Potential applications, limitations and technical problems are discussed.     

Extremes of human heat tolerance: life at the precipice of thermoregulatory failure

1. Human life is sustainable only below an internal temperature of roughly 42–44 °C. Yet our ability to survive at severe environmental extremes is testimony to the marvels of integrative human physiology.

2. One approach to understanding human thermoregulatory capacity is to examine the upper limits of thermal balance between man and the air environment, i.e. the maximal environmental conditions under which humans can maintain a steady-state core temperature. Heat acclimation expands the zone of thermal balance.

3. Human beings can and do, often willingly, tolerate extreme heat stresses well above these thermal balance limits. Survival in all such cases is limited to abbreviated exposure times, which in turn are limited by the robustness of the thermoregulatory response.

4. Figures are provided that relate tolerance time and the rate of change in core temperature to environmental characteristics based on data compiled from the literature.     

Intraspecific variation of thermal reaction norms for development in insects: New approaches and prospects

The main parameters (thermal constants) characterizing the effects of constant temperatures on the duration and rate of development in ectotherms are considered. The advantages and drawbacks of the linear and nonlinear models describing the dependence of the development rate on temperature are discussed. The main patterns of interspecific variation of thermal constants in insects are described. The development of new ideas in the study of intraspecific variation of thermal reaction norms for development in insects is examined. The discrepancies in the data and their interpretation in this field are shown to result mostly from using the traditional methods of determining thermal constants. According to this method, the development rates calculated as reciprocals of the mean development times at each experimental temperature are used for regression analysis. The standard errors calculated according to this method are usually too large. Instead, a fundamentally new method is employed by the authors, according to which the individual development rates calculated for each individual are used for regression analysis of the reciprocals of the mean development times. This method reduces the standard errors of thermal constants by about an order and reveals significant differences between populations and other groups of insects. New data on intraspecific variation of the thermal reaction norms for development in Myrmica ants, the linden bug Pyrrhocoris apterus, and Calliphora blowflies are briefly described and discussed. The possible adaptive significance of these forms of intraspecific variation is discussed. The prospects of research in this new field are outlined.     

Effect of short-term cold temperature stress on development,survival and reproduction of Dysdercus koenigii (Hemiptera: Pyrrhocoridae)

Red cotton bug Dysdercus koenigii F. (Hemiptera: Pyrrhocoridae), is found destructive pest in various cotton growing areas. Under natural conditions insects are highly subjected to thermal stresses. In present work the developmental duration and survival rate of all immature stages, adult longevity and reproduction of D. koenigii by exposed to rapid changes in very low temperatures were studied. When 3 h short-stress of low temperatures (12–0 °C) was given to different stages of D. koenigii, the results revealed that survival rate of all stages were significantly reduced. Survival rate of female was significantly higher than male after exposed to cold temperature stress. Mating percentage, fecundity and hatching percentage were decreased significantly with the decrease of short-term cold temperature stress. Based on these results, we concluded that the developmental duration, survival rate and reproduction of D. koenigii significantly affected when they exposed to short term cold temperature stress.     

Thermal biology of flight in a butterfly: genotype,flight metabolism,and environmental conditions

Knowledge of the effects of thermal conditions on animal movement and dispersal is necessary for a mechanistic understanding of the consequences of climate change and habitat fragmentation. In particular, the flight of ectothermic insects such as small butterflies is greatly influenced by ambient temperature. Here, variation in body temperature during flight is investigated in an ecological model species, the Glanville fritillary butterfly (Melitaea cinxia). Attention is paid on the effects of flight metabolism, genotypes at candidate loci, and environmental conditions. Measurements were made under a natural range of conditions using infrared thermal imaging. Heating of flight muscles by flight metabolism has been presumed to be negligible in small butterflies. However, the results demonstrate that Glanville fritillary males with high flight metabolic rate maintain elevated body temperature better during flight than males with a low rate of flight metabolism. This effect is likely to have a significant influence on the dispersal performance and fitness of butterflies and demonstrates the possible importance of intraspecific physiological variation on dispersal in other similar ectothermic insects. The results also suggest that individuals having an advantage in low ambient temperatures can be susceptible to overheating at high temperatures. Further, tolerance of high temperatures may be important for flight performance, as indicated by an association of heat‐shock protein (Hsp70) genotype with flight metabolic rate and body temperature at takeoff. The dynamics of body temperature at flight and factors affecting it also differed significantly between female and male butterflies, indicating that thermal dynamics are governed by different mechanisms in the two sexes. This study contributes to knowledge about factors affecting intraspecific variation in dispersal‐related thermal performance in butterflies and other insects. Such information is needed for predictive models of the evolution of dispersal in the face of habitat fragmentation and climate change.     

Temperature-dependent development of Chilocorus bipustulatus (Coleoptera: Coccinellidae)

The effect of temperature on development and survival of Chilocorus bipustulatus L. (Coleoptera: Coccinellidae), a predator of many scale insects, was studied under laboratory conditions. The duration of development of egg, first, second, third, and fourth larval instars, pupa, and preovioposition period at seven constant temperatures (15, 17.5, 20, 25, 30, 32.5, and 35°C) was measured. Development time decreased significantly with increasing temperature within the range 15-30°C. Survival was higher at medium temperatures (17.5-30(ο)C) in comparison with that at more extreme temperature regimens (15 and >30(ο)C). Egg and first larval instars were the stages where C. bipustulatus suffered the highest mortality levels at all temperatures. The highest survival was recorded when experimental individuals were older than the third larval instar. Thermal requirements of development (developmental thresholds, thermal constant, optimum temperature) of C. bipustulatus were estimated with application of linear and one nonlinear models (Logan I). Upper and lower developmental thresholds ranged between 35.2-37.9 and 11.1-13.0°C, respectively. The optimum temperature for development (where maximum rate of development occurs) was estimated at between 33.6 and 34.7°C. The thermal constant for total development was estimated 474.7 degree-days.     

Thermal shock and dilution shock as the causes of freezing injury

We suggest that during slow freezing, cellular membranes are altered by the hypertonic solutions produced. This alteration in itself does not cause membrane leakage of normally impermeant solutes but it renders the cells susceptible to solute leakage on the application of a stress, which is provided during freezing by the reduction in temperature (thermal shock) and during thawing by dilution (dilution shock).During slow freezing the effects of cooling rate changes are due to the different times available for the hypertonic solutions to affect the membrane. At a given cooling rate cryoprotective agents reduce the effect on the cells at each temperature during freezing perhaps by reducing the ionic strength. The thermal shock stress during cooling and the dilution shock during thawing thus damages the cells less. With rapid freezing, there is insufficient time for these effects to take place during cooling, which allows the cells to reach low temperatures without thermal shock damage. However, the presence of extracellular ice and the formation of intracellular ice provide hypertonic conditions that render the cells liable to dilution shock on thawing. The slower the rate of thawing of rapidly cooled cells the greater will be the damage from this dilution shock.     

Thermal sensitivity of escape response performance by the scallop Placopecten magellanicus: Impact of environmental history

To examine the impact of environmental history on the thermal sensitivity of escape response performance in juvenile giant scallops, Placopecten magellanicus, we compared animals sampled in late May, when water temperatures and day length were increasing, to animals sampled in late September, when water temperature and day length were decreasing. Habitat temperature was approximately 12 °C at both sampling times. For May scallops, performance was better at 6 than at 12 or 18 °C whereas September scallops performed better at 6 and 12 °C than at 19 °C. Regardless of environmental history, the rate of phasic contractions consistently declined at 18–19 °C, due to a decrease in the number of phasic contractions. Force measurements during escape responses of May scallops showed that phasic force production and the minimal interval between contractions changed little with temperature, whereas the minimum and mean durations of phasic contractions decreased as temperature rose. Phasic contraction rate in the first series increased with temperature. Reliance upon tonic contractions was higher in scallops tested at 18 °C than in those tested at 6 °C. Environmental history, more than habitat temperature at the time of sampling, seems to set the thermal sensitivity of phasic contraction rate in P. magellanicus. Phasic force production did not change within the thermal range tested.     

Stable and variable life‐history responses to temperature and photoperiod in the beet webworm,Loxostege sticticalis

The beet webworm, Loxostege sticticalis L. (Lepidoptera: Crambidae), unlike many temperate insects and despite its wide distribution range, has a geographically stable value of the critical photoperiod for diapause induction. It has thus been hypothesized that the species could adjust its life cycle to different climates in an alternative way, which should be reflected in geographical variation and/or environmental plasticity of some other ecophysiological trait. Three remote populations of the beet webworm were studied. The insects were reared from egg to adult at several combinations of temperature and photoperiod in order to measure development times of all the immature stages and pre‐pupal body weight, and to characterize the sensitivity of these life‐history traits to the two ecological factors. The thermal reaction norms for immature development appeared to be significantly different in the three populations. There was also a significant effect of photoperiod on development time as well as on the thermal sensitivity and lower temperature threshold for larval development. Pre‐pupae from the northernmost population were heavier and their body mass was more strongly affected by photoperiod than in the other two, but attainment of a greater weight under short‐day conditions, especially combined with higher temperatures, was common for all the three populations. Nevertheless, all the discovered geographical and environmentally induced differences in life‐history traits were very small and their adaptive significance remains problematic.     

High temperature pulses decrease indirect chilling injury and elevate ATP levels in the flesh fly, Sarcophaga crassipalpis

Indirect chilling injury commonly occurs during long-term exposure to low temperature in many organisms including insects. A previous study revealed increased rates of survival and reduced cold injury in flesh flies, Sarcophaga crassipalpis, that experienced an intermittent pulse of high temperature during a low-temperature regiment. We extended these studies by determining survival rates and ATP levels for flies that had undergone continuous long-term exposure at 0 °C versus those experiencing a 24-h warming pulse of either 15 or 20 °C. Survival among flies that had undergone a warming pulse was significantly greater than for flies that were maintained continuously at 0 °C. Furthermore, ATP levels of flies that had experienced a warming pulse were significantly higher than those of flies maintained at 0 °C. These data suggest that brief warming pulses during long-term cold storage allow regeneration of energy reserves that promote survival and reduce indirect chilling injury.     

Resistance to thermal stress in adult Drosophila buzzatii: acclimation and variation among populations

Survival after heat stress was examined in adult Drosophila buzzatii from seven localities. Males and females were conditioned by a non-lethal high temperature before exposure to a severe thermal stress. Variable times elapsed between conditioning, either as adults or pupae, and exposure to the stress were used, and experimental times to the stress ranged from 2 to 96 hours. Survival after stress varied among populations, and differences generally were consistent across conditioning treatments and across experiments. Resistance to thermal stress was much higher following one conditioning bout 2–4 hours before exposure to a severe stress than when the time elapsed between conditioning and exposure was increased to 24 or more hours. Significantly more adults survived the stress if conditioned 4 days before exposure to the thermal stress, either as adults or as pupae, than if not conditioned. The rank order of resistance roughly followed that predicted from the climatic conditions of the localities of origin.     

Thermal, metabolic, and cardiovascular responses to various degrees of cold stress.

The metabolic, thermal, and cardiovascular responses of two male Caucasians to 1 2 h exposure to ambient temperature ranging between 28 degrees C and 5 degrees C were studied and related to the respective ambient temperatures. The metabolic heat production increased linearly with decreasing ambient temperature, where heat production (kcal times m- minus 2 times h- minus 1) = minus 2.79 Ta degrees C + 103.4, r = -0.97, P smaller than 0.001. During all exposures below 28 degrees C, the rate of decrease in mean skin temperature (Tsk) was found to be an exponential function dependent upon the ambient temperature (Ta) and the time of exposure. Reestablishment of Tsk steady state occurred at 90-120 min of exposure, and the time needed to attain steady state was linearly related to decreasing Ta. The net result was that a constant ratio of 1.5 of the external thermal gradient to the internal thermal gradient was obtained, and at all experimental temperatures, the whole body heat transfer coefficient remained constant. Cardiac output was inversely related to decreasing Ta, where cardiac output (Q) = minus 0.25 Ta degrees C + 14.0, r = minus 0.92, P smaller than 0.01. However, the primary reason for the increased Q, the stroke output, was also described as a third-order polynomial, although the increasing stroke volume throughout the Ta range (28-5 degrees C) was linearly related to decreasing ambients. The non-linear response of this parameter which occurred at 20 degrees C larger than or equal to Ta larger than or equal to 10 degrees C suggested that the organism's cardiac output response was an integration of the depressed heart rate response and the increasing stroke output at these temperatures.     

Induction of rapid cold hardening by cooling at ecologically relevant rates in Drosophila melanogaster

Over a decade ago it was hypothesized that the rapid cold hardening process allows an organism's overall cold tolerance to track changes in environmental temperature, as would occur in nature during diurnal thermal cycles. Although a number of studies have since focused on characterizing the rapid cold hardening process and on elucidating the physiological mechanisms upon which it is based, the ecological relevance of this phenomenon has received little attention. We present evidence that in Drosophila melanogaster rapid cold hardening can be induced during cooling at rates which occur naturally, and that the protection afforded in such a manner benefits the organism at ecologically relevant temperatures. Drosophila melanogaster cooled at natural rates (0.05 and 0.1 degrees C min(-1)) exhibited significantly higher survival after one hour of exposure to -7 and -8 degrees C than did those directly transferred to these temperatures or those cooled at 0.5, or 1.0 degrees C min(-1). Protection accrued throughout the cooling process (e.g., flies cooled to 0 degrees C were more cold tolerant than those cooled to 11 degrees C). Whereas D. melanogaster cooled at 1.0 degrees C min(-1) had a critical thermal minimum (i.e., the temperature at which torpor occurred) of 6.5+/-0.6 degrees C, those cooled at an ecologically relevant rate of 0.1 degrees C min(-1) had a significantly lower value of 3.9+/-0.9 degrees C.     

Destabilization of mayonnaise induced by lipid crystallization upon freezing

The thermal and rheological history of mayonnaise during freezing and its dispersion stability after the freeze-thaw process were investigated. Mayonnaise was cooled to freeze and stored at ?20 to ?40 °C while monitoring the temperature; penetration tests were conducted on the mayonnaise, which was sampled at selected times during isothermal storage at ?20 °C. Significant increases in the temperature and stress values due to water-phase crystallization and subsequent oil-phase crystallization were observed. The water phase crystallized during the cooling step in all the tested mayonnaise samples. The oil phases of the prepared mayonnaise (with rapeseed oil) and commercial mayonnaise crystallized during isothermal storage after 6 and 4 h, respectively, at ?20 °C. The dispersion stability was evaluated from the separation ratio, which was defined as the weight ratio of separated oil after centrifuging to the total amount of oil in the commercial mayonnaise. The separation ratio rapidly increased after 4 h of freezing. This result suggests that crystallization of the oil phase is strongly related to the dispersion stability of mayonnaise.     

Relevance of body size and shell colouration for thermal absorption and heat loss in white garden snails,Theba pisana (Helicidae), from Northern France

The internal temperature of land snails depends on environmental factors, such as exposure to electromagnetic radiation and airflow as well as biotic factors including shell size, shell colouration and thickness or the resting position of the snail. In controlled field experiments, we quantified heating by thermal absorption of light and airflow-induced heat loss in the white garden snail, Theba pisana, from Normandy, France. Heating experiments revealed a significant positive relation of the internal body temperature with illumination period, shell temperature and air temperature at different times of day. The size of the snails was negatively related with both of the given illumination times: smaller animals heated up stronger than larger ones. The temperature at the surface of the shell significantly depended on the illumination period and the time of day. An AIC-based quality assessment of multiple linear modelling showed that, for explaining both shell surface and internal temperature of the soft body, several factors, i.e., exposure time, daytime, shell size and colouration contributed to the best models, respectively. Similarly, heat loss of the soft body after and during exposure of the snails to sunlight by a constant airflow depended on the initial body temperature, shell size, colouration and ambient air temperature. Our study revealed also the importance of both shell size and colouration for the loss of body temperature under natural conditions: small and banded animals that had heated up to temperatures above 30 °C cooled down faster than large and un-banded ones.     

Effect of temperature on development and survival in Delias nigrina (Fabricius) (Lepidoptera: Pieridae)

Abstract The effect of temperature on rate of development and survival of the immature stages of a subtropical population of the black jezebel, Delias nigrina , was studied under laboratory conditions at a range of constant temperatures. Mean developmental times from first-instar larva to adult varied from 29 days at 27°C to 52 days at 19°C; the development threshold temperature and thermal constant were estimated to be 9°C and 494 degree-days, respectively. Larval developmental rates reached physiological maximum at the higher temperatures tested (25−27°C). Pupal development, by contrast, was not affected in the same way as larvae by higher temperature. Survival of the immature stages varied inversely with temperature: survival was highest at 19°C and significantly reduced at 27°C. Mortality at the higher temperature was attributable mainly to final-instar larvae and pupae. These findings indicate that, compared with other tropical pierids that have been studied, D. nigrina has: (i) a comparatively low temperature threshold; (ii) a slow rate of development; and (iii) a poor tolerance to moderately high temperatures. Physiologically, these features are more characteristic of a temperate butterfly than a tropical one. This physiological response appears to be reflected by the temperate nature of the genus as a whole, which may be related to its period of origin and evolution during past climatic events.     

Temperature Effects on Survival and Development of Heleidomermis magnapapula in the Laboratory

The mermithid Heleidomermis magnapapula Poinar and Mullens, a parasite of the biting midge Culicoides variipennis (Coquillett), was exposed to constant temperatures in the laboratory. Survival of the free-living stages and development times of eggs and the parasitic phase were inversely related to temperature. Average preparasite longevity was 70, 46, 42, and 22 hours at 15.6, 21.1, 26.7, and 32.2 C, respectively. Females survived significantly longer than males. Longevity in days (females/males) at different temperatures was 17.3/11.0 at 4.4 C, 9.0/8.2 at 15.6 C, 5.9/5,1 at 21.1 C, 5.2/4.7 at 26.7 C, and 4.4/3.6 at 32.2 C. Embryogenesis required 44 ± 2 degree days above a thermal minimum of 10.1 C, while parasitic development in host larvae required 214 ± 10 degree days above a thermal minimum of 8.9 C. Parasite responses to temperature were very closely related to temperature-dependent host development patterns.     

Effects of cooling rate and storage temperature on equine spermatozoal motility parameters

Two experiments were conducted to examine the effects of cooling rate and storage temperature on motility parameters of stallion spermatozoa. In Experiment 1, specific cooling rates to be used in Experiment 2 were established. In Experiment 2, three ejaculates from each of two stallions were diluted to 25 x 10(6) sperm/ml with 37 degrees C nonfat dry skim milk-glucose-penicillin-streptomycin seminal extender, then assigned to one of five treatments: 1) storage at 37 degrees C, 2) storage at 25 degrees C, 3) slow cooling rate to and storage at 4 degrees C, 4) moderate cooling rate to and storage at 4 degrees C, and 5) fast cooling rate to and storage at 4 degrees C. Total spermatozoal motility (TSM), progressive spermatozoal motility (PSM), and spermatozoal velocity (SV) were estimated at 6, 12, 24, 48, 72, 96 and 120 h postejaculation. The longevity of spermatozoal motility was greatly reduced when spermatozoa were stored at 37 degrees C as compared to lower spermatozoal storage temperatures. At 6 h postejaculation, TSM values (mean % +/- SEM) of semen stored at 37 degrees C, slowly cooled to and stored at 25 degrees C or slowly cooled to and stored at 4 degrees C were 5.4 +/- 1.1, 79.8 +/- 1.6, and 82.1 +/- 1.6, respectively. Mean TSM for semen that was cooled to 4 degrees C at a slow rate was greater (P<0.05) than mean TSM of semen cooled to 4 degrees C at a moderate rate for four of seven time periods (6, 24, 72 and 120 h), and it was greater (P<0.05) than mean TSM of semen cooled to 4 degrees C at a fast rate for five of seven time periods (6, 12, 24, 72 and 120 h). Mean TSM of semen cooled to 4 degrees C at a slow rate was greater (P<0.05) than mean TSM of semen cooled to 25 degrees C for five of seven time periods (24 to 120 h). A similar pattern was found for PSM. Mean SV of semen cooled to 4 degrees C at a slow rate was greater (P<0.05) than mean SV of semen cooled to 25 degrees C for all time periods. A slow cooling rate (initial cooling rate of -0.3 degrees /min) and a storage temperature of 4 degrees C appear to optimize liquid preservation of equine spermatozoal motility in vitro.