Rate Isomorphy Research Articles

Developmental Biology of Forensically Important Beetle, Necrophila (Calosilpha) brunnicollis (Coleoptera: Silphidae).

The postmortem interval (PMI) estimation, in cases where the body was discovered in an advanced stage of decomposition, is predominantly based on entomological evidence. However, very few forensically important species are sufficiently known in detail to allow a practical application. One of them is the carrion beetle, Necrophila (Calosilpha) brunnicollis (Kraatz, 1877). Its development from egg to adulthood was studied under a range of ecologically relevant constant temperatures to find parameters of thermal summation models. Developmental sexual dimorphism and the presence of developmental rate isomorphy were investigated. Herein we present the lower developmental thresholds and sum of effective temperatures for all developmental stages of N. brunnicollis (egg, first-third larval instar, postfeeding stage, and pupae). We did not find any evidence of developmental sexual dimorphism nor was the presence of developmental rate isomorphy confirmed. Our results present the first thermal summation model of the East Asian carrion beetle that can be used for the PMI estimation.

Rapid shifts in the thermal sensitivity of growth but not development rate causes temperature–size response variability during ontogeny in arthropods

Size at maturity in ectotherms commonly declines with warming. This near‐universal phenomenon, formalised as the temperature–size rule, has been observed in over 80% of tested species, from bacteria to fish. The proximate cause has been attributed to the greater temperature dependence of development rate than growth rate, causing individuals to develop earlier but mature smaller in the warm. However, few studies have examined the ontogenetic progression of the temperature–size response at high resolution. Using marine planktonic copepods, we experimentally determined the progression of the temperature–size response over ontogeny. Temperature–size responses were not generated gradually from egg to adult, contrary to the predictions of a naïve model in which development rate was assumed to be more temperature‐dependent than growth rate, and the difference in the temperature dependence of these two rates remained constant over ontogeny. Instead, the ontogenetic progression of the temperature–size response in experimental animals was highly episodic, indicating rapid changes in the extent to which growth and development rates are thermally decoupled. The strongest temperature–size responses occurred temporally mid‐way through ontogeny, corresponding with the point at which individuals reached between ~5 and 25% of their adult mass. Using the copepod Oithona nana, we show that the temperature‐dependence of growth rate varied substantially throughout ontogeny, whereas the temperature dependence of development rate remained constant. The temperature‐dependence of growth rate even exceeded that of development rate in some life stages, leading to a weakening of the temperature–size response. Our analyses of arthropod temperature–size responses from the literature, including crustaceans and insects, support these conclusions more broadly. Overall, our findings provide a better understanding of how the temperature–size rule is produced over ontogeny. Whereas we find support for the generality of developmental rate isomorphy in arthropods (shared temperature dependence of development rate across life stages), this concept appears not to apply to growth rates.

Arthropods life cycle and temperature: Beyond isomorphy hypothesis

In poikilotherms, developmental time and adult lifespan are biological traits driven by temperature although their underlying physiological mechanisms differ. The developmental theory of ageing predicts a positive correlation between these two traits without confirming a genetic or causal relationship. The developmental rate isomorphy hypothesis established that the proportionality in the duration of each pre-imaginal stage with respect to total developmental time does not vary with temperature. This may have important evolutionary implications. We conducted an analysis with arthropods of agronomic interest to study if the hypothesis could be extended to the total lifespan of poikilotherms, including adult lifespan. We showed that isomorphy could be acceptable for a global description of this relationship. However a general model of power law type is more appropriate for characterizing the relationship between developmental time and adult lifespan. In this model, the shape of the curve is a constant characteristic, but the parameters that control it depend on the functional type of the arthropod (phytophagous, predator or parasitoid). Presumably this power law could be extended to all arthropods of agricultural interest, and more generally to all arthropod.

The effect of temperature on the developmental rates of seedling emergence and leaf-unfolding in two dwarf bamboo species

The mean and variance of developmental rates of bamboos at different temperatures follow a power law. The rate isomorphy hypothesis, demonstrated in insects and mites, does not hold in bamboos. The developmental time of plants and poikilotherms can be significantly affected by temperature. Developmental rate (i.e. the reciprocal of developmental time) of arthropods and germination rate of some plant seeds have been demonstrated to follow a linear function with temperature. The rate isomorphy hypothesis in entomology suggests a lower developmental threshold below which development of all life stages terminates. If this hypothesis also holds for plants, the estimated lower threshold for one development stage could be used for predicting thresholds of other stages. Here, we tested this hypothesis to compare the developmental time of seedling emergence and the time from seedling emergence to the unfolding of the third leaf in two bamboo species. We used five constant thermal environments from 18.5 to 28.5 °C with an increment of 2.5 °C. Both species showed a linear relationship between temperature and developmental rate, with the mean and variance of developmental rates following a power law. Using the bootstrap percentile method, we showed that the isomorphy hypothesis does not hold for both species. The effect of temperature on the survival rate at the time of seedling emergence differed significantly between the two species.

Thermal development of Cephalonomia tarsalis (Hymenoptera: Bethylidae) parasitoid of the saw-toothed stored product beetles of the genus Oryzaephilus sp. (Coleoptera: Sylvanidae)

The effect of temperature on the development and survival of Cephalonomia tarsalis (Ashmead) (Hymenoptera: Bethylidae), larval ectoparasitoid of beetles of Oryzaephilus sp. (Coleoptera: Silvanidae) was studied in the laboratory. Durations of the development of the egg, larva and pupa were measured in eight constant temperatures (15, 17.5, 20, 25, 30, 32.5, 35 and 37.5°C) parasitizing larvae of the saw-toothed beetle Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). The duration of development was decreased with temperature increase within the range 17.5–32.5°C. Survival was higher when immatures were exposed to medium temperatures (20–30°C) compared with those lived in a more extreme temperature regime (<20 and >30°C). Wasps failed to complete their development at 15 and 37.5°C. Thermal parameters (upper, lower and optimum developmental threshold, thermal constant) were estimated by fitting the linear and a non-linear (Logan I) model to our data. Upper and lower developmental thresholds ranged between 35.1–37.0°C and 13.2–13.8°C, respectively. The optimum temperature for development was estimated between 33.6°C and 34.6°C. Tests for developmental rate isomorphy (DRI) showed that change in the average proportion of time spent in each developmental stage was marginally significant, proving that development of C. tarsalis is probably incompatible with DRI. However, this conclusion is questionable given that lower developmental thresholds did not differ significantly among various developmental stages (bootstrap test). Thermal constant for total development was calculated 212.4 degree-days. Our results are discussed not only on the basis of thermal biology, but also of improving the efficiency of C. tarsalis as biocontrol agent.

Analyses of Developmental Rate Isomorphy in Ectotherms: Introducing the Dirichlet Regression.

Temperature drives development in insects and other ectotherms because their metabolic rate and growth depends directly on thermal conditions. However, relative durations of successive ontogenetic stages often remain nearly constant across a substantial range of temperatures. This pattern, termed ‘developmental rate isomorphy’ (DRI) in insects, appears to be widespread and reported departures from DRI are generally very small. We show that these conclusions may be due to the caveats hidden in the statistical methods currently used to study DRI. Because the DRI concept is inherently based on proportional data, we propose that Dirichlet regression applied to individual-level data is an appropriate statistical method to critically assess DRI. As a case study we analyze data on five aquatic and four terrestrial insect species. We find that results obtained by Dirichlet regression are consistent with DRI violation in at least eight of the studied species, although standard analysis detects significant departure from DRI in only four of them. Moreover, the departures from DRI detected by Dirichlet regression are consistently much larger than previously reported. The proposed framework can also be used to infer whether observed departures from DRI reflect life history adaptations to size- or stage-dependent effects of varying temperature. Our results indicate that the concept of DRI in insects and other ectotherms should be critically re-evaluated and put in a wider context, including the concept of ‘equiproportional development’ developed for copepods.

Development response of Spodoptera exigua to eight constant temperatures: Linear and nonlinear modeling

Temperature-dependent development of Spodoptera exigua (Hübner) were evaluated at eight constant temperatures of 12, 15, 20, 25, 30, 33, 34 and 36°C with a variation of 0.5°C on sugar beet leaves. No development occurred at 12°C and 36°C. Total developmental time varied from 120.50days at 15°C to 14.50days at 33°C. As temperature increased from 15°C to 33°C, developmental rate (1/developmental time) of S. exigua increased but declined at 34°C. The lower temperature threshold (Tmin) was estimated to be 12.98°C and 12.45°C, and the thermal constant (K) was 294.99 DD and 311.76 DD, using the traditional and Ikemoto–Takai linear models, respectively. The slopes of the Ikemoto–Takai linear model for different immature stages were different, violating the assumption of rate isomorphy. Data were fitted to three nonlinear models to predict the developmental rate and estimate the critical temperatures. The Tmin values estimated by Lactin-2 (12.90°C) and SSI (13.35°C) were higher than the value estimated by Briere-2 (8.67°C). The estimated fastest development temperatures (Tfast) by the Briere-2, Lactin-2 and SSI models for overall immature stages development of S. exigua were 33.4°C, 33.9°C and 32.4°C, respectively. The intrinsic optimum temperature (TΦ) estimated from the SSI model was 28.5°C, in which the probability of enzyme being in its native state is maximal. The upper temperature threshold (Tmax) values estimated by these three nonlinear models varied from 34.00°C to 34.69°C. These findings on thermal requirements can be used to predict the occurrence, number of generations and population dynamics of S. exigua.

Effect of Temperature on the Development of &lt;I&gt;Laodelphax striatellus&lt;/I&gt; (Homoptera: Delphacidae)

Temperature has a significant influence on the development of Laodelphax striatellus (Fallén), an important rice pest insect in east Asia. We set eight constant temperatures from 18 to 32 degrees C in 2 degrees C-increments to check the effect of temperature on the developmental rate of this insect species. The developmental durations of eggs and nymphs were observed daily. To ensure the accuracy of developmental durations, 500 initial samples were taken for the nymphal stage at each temperature. Performance-2 model was used to fit these data because this model can provide the lower and upper developmental thresholds simultaneously. The estimate of lower developmental thresholds of eggs (10.0 degrees C) was different from that of nymphs (7.5 degrees C). And the estimate of upper developmental thresholds of eggs (35.5 degrees C) was also different from that of nymphs (30.2 degrees C). However, for male and female nymphs, the difference in the lower developmental threshold is nonsignificant, and the difference in the upper developmental thresholds is very small (95% confidence interval of the difference: [0.007 degrees C, 0.043 degrees C]). The rate isomorphy hypothesis considers that the lower developmental thresholds of different stages for the same insect might be constant. However, the current study provides a counterexample of this hypothesis that the lower developmental threshold of eggs is different from that of nymphs. Thus, we demonstrate that the rate isomorphy hypothesis does not apply all insects. In addition, we used a popular nonlinear model, Lactin model, to fit the developmental rate data of our experiment. And we found that the estimates of lower and upper developmental thresholds by using Performance-2 model were very approximate to those by using Lactin model. The current study provides reliable estimates of thermal parameters for L. striatellus by using large experimental samples at different temperatures. It would be useful for exploring the relationship of climate change and the outbreak of this insect on rice.

Control of preimaginal development by photoperiod and temperature in the dock leaf beetle Gastrophysa viridula (De Geer) (Coleoptera, Chrysomelidae)

Development times of preimaginal stages and immature adult body mass of the dock leaf beetle Gastrophysa viridula from Bryansk (53°N, 34°E) were determined at six constant temperatures ranging from 16 to 26°C and at two photoperiods, 12L: 12D or 22L: 2D. The lower developmental threshold (LDT) and sum of degreedays (SDD) were calculated for eggs, larvae, and pupae; the values for the total preimaginal development were 7.9°C and 274.8 °C×d, respectively. The thermal reaction norms for preimaginal development were not affected by photoperiod, although the adult body mass was on average greater under short-day conditions. Our results confirm the previously published data on G. viridula concerning diapause induction by shorter daylengths, greater body mass under lower temperatures, and narrowing of the thermal optimum range during preimaginal development. The thermal reaction norms for larval development were shown to be the same in individuals that died during the pupal stage, and in those that successfully emerged as adults. Our results are more precise than the previous data on this species due to a larger sample size, careful control of rearing conditions, and the use of an alternative method for calculating LDT and SDD. In particular, a more accurate estimation of LDTs allowed us to demonstrate that rate isomorphy was violated in this species, contrary to what had been stated by Honěk and co-authors (2003).

Testing the rate isomorphy hypothesis using five statistical methods

Abstract Organisms are said to be in developmental rate isomorphy when the proportions of developmental stage durations are unaffected by temperature. Comprehensive stage‐specific developmental data were generated on the cabbage beetle, Colaphellus bowringi Baly (Coleoptera: Chrysomelidae), at eight temperatures ranging from 16°C to 30°C (in 2°C increments) and five analytical methods were used to test the rate isomorphy hypothesis, including: (i) direct comparison of lower developmental thresholds with standard errors based on the traditional linear equation describing developmental rate as the linear function of temperature; (ii) analysis of covariance to compare the lower developmental thresholds of different stages based on the Ikemoto‐Takai linear equation; (iii) testing the significance of the slope item in the regression line of versus temperature, where p is the ratio of the developmental duration of a particular developmental stage to the entire pre‐imaginal developmental duration for one insect or mite species; (iv) analysis of variance to test for significant differences between the ratios of developmental stage durations to that of pre‐imaginal development; and (v) checking whether there is an element less than a given level of significance in the p‐value matrix of rotating regression line. The results revealed no significant difference among the lower developmental thresholds or among the aforementioned ratios, and thus convincingly confirmed the rate isomorphy hypothesis.

Common-intersection hypothesis of development rate lines of ectotherms within a taxon revisited

The relationship between development rate of an ectotherm and temperature in experiments where insects or mites are reared under several constant temperatures, while non-linear over the entire range, can be approximately described by a line in the mid-temperature range. It was hypothesized that the development rate lines of ectotherms within a taxon such as a family would have a common intersection. Thus for a given temperature, the development time should be the same for all the species within any specified taxon. In the current study, the data on temperature-dependent development rates of species of the Aphididae and Tetranychidae families were used to test the validity of the common-intersection hypothesis. The hypothesis was supported with either dataset used. In addition, the current study tested the common-intersection hypothesis through mathematical analysis on the basis of two linear relationships (i.e., the linear relationship between temperature and development rate and that between the lower developmental threshold and the sum of effective temperatures). An attempt was made to combine the rate isomorphy hypothesis that all the lower developmental thresholds of different stages were assumed to be equal for a single species with the common-intersection hypothesis for related species within a taxon and hypothesize that if these two hypotheses hold, then for any developmental stages a common temperature of all stages should exist.

Photoperiod modifies thermal reaction norms for growth and development in the red poplar leaf beetle Chrysomela populi (Coleoptera: Chrysomelidae)

Regression lines of development rate on temperature appeared significantly different between long (22h) and short (12h) day conditions and intersected each other at 23.8°С. Thus, the rate of growth and development was higher at temperatures below the intersection point under short-day but above the intersection point it was higher under long day. Ecological relevance of this effect seems as follows: in autumn, as nights become longer and average daily temperature decreases, larvae have to speed up their development because it is only imago that overwinters. Conversely, midsummer offers long days and usually higher temperature, so again it is advantageous to develop as fast as possible in order to have at least one more generation per year. These results are compared with other studies showing interactions between photoperiod and temperature, and some possible general patterns are outlined. The lower thermal threshold for larval development depended on photoperiodic conditions; therefore rate isomorphy must be violated in this species. Development at higher temperatures generally resulted in smaller adults, as is usual with ectotherms according to the “temperature-size rule”, but body weight depended significantly on temperature only under short day. Our estimates of the lower temperature thresholds for growth and development in both cases did conform to the generalization made previously by Walters and Hassall (2006) in spite of another formula used by us. We briefly discuss this phenomenon and argue that relative position of these thresholds can be explained mathematically and per se may lack any biological sense.

Ontogenetic stage-dependent effect of temperature on developmental and metabolic rates in a holometabolous insect

Different hypotheses attempt to explain how different stages of organisms with complex life cycles respond to environmental changes. Most studies have focused at the among-species level showing similar responses to temperature throughout ontogeny. However, there is no agreement about the pattern expected at the intraspecific scale where a strong selective effect is expected. In this paper, we studied the effects of thermal treatments on a life history trait (developmental rate) and a physiological trait (metabolic rate) during development in the fruitfly Drosophila buzzatii. First, we estimated the rate of development during larval life (LDR) and the pupal stage (PDR) in flies derived from two natural populations exposed to several thermal treatments. Our results showed that the developmental rate ratio, LDR/PDR, did not vary between populations, and that the effects of thermal treatments were stage specific. Second, we studied the relationship between developmental rate (DR) and metabolic rate (MR) in each life cycle stage. We found that allometric relationships between DR and MR varied throughout ontogeny, a pattern that shed light on the mechanisms responsible for thermal plasticity. We conclude that, although different populations may show developmental rate isomorphy; larvae and pupae may choose alternative “decisions” in terms of life-history evolution and physiological traits when confronted to different thermal environments.

Preimaginal Development Response to Constant Temperatures inHypera postica(Coleoptera: Curculionidae): Picking the Best Model

Immature survival and development of alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), were examined at 15 constant temperatures ranging from 9 to 37 degrees C. At 9 and 37 degrees C, eggs did not develop. Embryos developed to adulthood between 11.5 and 36 degrees C, although survival was low at both ends of the temperature range. Distribution of development times for all stages of alfalfa weevil were skewed toward longer times mainly at moderate temperatures. Constant proportion of time spent in egg, larva, and pupa indicated rate isomorphy within the range 14-31.5 degrees C. No significant difference was shown between development time of males and females at any of the temperatures tested. Two linear and 23 nonlinear models were fitted to describe development rate of immature stages of H. postica as a function of temperature, as well as estimating the thermal constant and critical temperatures (i.e., T(min), T(opt), and T(max)). There was no statistical difference between the estimated parameters, using Ikemoto and ordinary linear methods. Of the nonlinear models fitted, the Logan-6/Lactin-2, Analytis-3/Briere-2, and Analytis-3/Briere-2 models were found to be the best for modeling development rate of egg, larva, and entire immature stages of H. postica, respectively. Our findings will be incorporated in more efficient phenological models of this pest and its population dynamics.

Study of intrapopulational variability of duration and temperature norms of development of the linden bug Pyrrhocoris apterus (Heteroptera, Pyrrhocoridae)

The existence of significant variability in duration and temperature norms of development has been shown for the first time between families within insect populations. This variability is infer-family and therefore has genetic basis. Revealed for the first time is the statistically significant positive correlations between the regression coefficient of the rate of development for temperature and the threshold of temperature for development of eggs and larvae from different families. The greater the slope of the regression line of the development rate for temperature, the higher the temperature threshold value in this particular family. These results demonstrate for the first time existence of genetic covariation between the regression coefficient and the temperature threshold within the insect populations. It is suggested that the intrapopulational genetic variability in the development time, regression coefficient, and the temperature threshold for development, which is the subject of natural selection, might be the source of the interpopulation and interspecies variability of the temperature reaction norms of development. It was found that value of the linear regression coefficient of development rates for temperature were statistically significantly higher, while the temperature threshold values--lower in eggs as compared with the corresponding parameters in larvae. These results obviously are in contradiction with the concept of the "developmental rate isomorphy in insects and mites" (Jarosik et al., 2002) which claims that the temperature threshold for development should be the same for all species cycle stages, so that only slopes of the regression lines can differ. Shown for the first time was the absence of genetic co-variability of the temperature reaction norms for development of different life cycle stages, i. e., eggs and larvae. This means that the regression coefficient (as well as the temperature requirement of the sum of the degree-days) and the temperature threshold for development in eggs and larvae are inherited independently and thereby they can change in evolution independently according to specific environmental condition under which these life cycle stages exist.

Effect of temperature on development and immature survival of Zygogramma bicolorata (Coleoptera: Chrysomelidae) under laboratory conditions

The effect of different constant temperatures (20, 25, 27, 30 and 35 °C) on life history stages of the Mexican chrysomelid beetle, Zygogramma bicolorata Pallister, fed on the weed Parthenium hysterophorus Linnaeus was investigated to analyse the development and survival of different life stages and the adult sex ratio. Fastest development and maximum survival were recorded at 27 °C. The first instar was the most vulnerable, while the pupa was least vulnerable. For complete development, the lower temperature threshold (t°C) was 18.5 °C and the thermal constant (K) was 480.8 day-degrees. A higher percentage of females was obtained at all temperatures; however, this was unaffected by the temperature regime. This study established that the percentage life span spent by immature stages was similar across all five temperatures, indicating developmental rate isomorphy. 27 °C was the most suitable temperature under controlled abiotic conditions for the propagation of Z. bicolorata, a bioagent for parthenium weed.

Contrast adaptation to time constraints on development of two pre-dispersal predators of dandelion (Taraxacum officinale) seed

Pre-dispersal seed predators of quickly maturing inflorescences of Asteraceae are constrained by shortage of development time. At seed dispersal, they should pupate or, if still immature, relocate into another inflorescence. To investigate how dominant coleopteran predators of dandelion seed, Glocianus punctiger (Curculionidae) and Olibrus bicolor (Phalacridae), cope with time limitation we combined observation (development and temperature of dandelion capitulum, thermal constants of predator development, age structure of larval populations at seed dispersal) and analogy (“rate isomorphy” in predator development, comparing “model” coleopteran species with similar temperature requirements). Development of a dandelion capitulum takes 21 days. The time available to G. punctiger (140–190 day degrees, development threshold 6.3°C) is sufficient to complete development and pupate after seed dispersal. By contrast, only 30–50 day degrees are available to O. bicolor (threshold 13.5°C) and this is not enough to complete development and consequently immature larvae should move to other capitula to continue feeding until pupation. These contrast strategies which are determined by this thermal adaptation, are accompanied by differences in larval morphology. The “cold adapted” G. punctiger has an apodous larva not capable of migrating between capitula while the “warm adapted” O. bicolor has a mobile campodeiform larva capable of migration.

Constant rate allocation in nymphal development in species of Hemiptera

Abstract. This study investigated the existence of rate isomorphy (the constant allocation of relative times to different stages of development under different abiotic conditions) in Macrolophus pygmaeus (Hemiptera: Miridae; a phytophagous and predatory insect). Replicated data were used from a range of temperatures regarding (i) the developmental period of each nymphal stage in relation to the total duration of nymph development, when feeding on three host plants either with different prey species or without prey, and (ii) its egg, total nymphal and preoviposition period, on two host plants, with different prey species. The proportion of time required for the development of each nymphal stage of M. pygmaeus is not different among the temperatures or the kind of food available. These proportions ranged among the different host plants, temperatures and prey presence/absence from 17.3–21.8% in the first, 14.5–18.8% in the second, 14.2–18.3% in the third, 16.5–21.0% in the fourth and from 25.4–30.6% in the fifth nymphal stage. Thus, temperature does not significantly affect the proportion of time spent in each nymphal stage and rate isomorphy exists in nymphal development. This phenomenon was also investigated using data from the literature, and it also occurs in several other Hemiptera species. Therefore, there appears to be a constant time allocation in the nymphal development of the higher taxonomic groups of insects. However, for M. pygmaeus, rate isomorphy does not hold when considering egg‐to‐egg development and the relative duration of times to egg hatch, total nymphal development and preoviposition period. The ecophysiological implications of this rate isomorphy phenomenon are discussed in relation to endocrinological mechanisms. Apart from its theoretical interest, the existence of rate isomorphy simplifies studies on the rate of development and the estimation of thermal constants of an insect, which are essential for the prediction of insect population dynamics. It is also proposed that the term ‘rate isomorphy’ does not strictly describe the phenomenon, and it is suggested that ‘constant rate allocation’ would be a more suitable term.

Temperature and development of central European species of Amara (Coleoptera: Carabidae)

Development rates of the eggs of 9 species, larvae of 6 species and pupae of 6 species of the genus Amara (Coleoptera: Carabidae) were recorded at five constant temperatures between 17 and 28°C, and thermal constants for each development stage calculated. The lower development threshold varied between 9.2-13.5°C for different stages and species. Rate isomorphy, which implies the existence of a common temperature threshold for all development stages, was demonstrated in 5 species. The sum of effective temperatures differed between stages. On average the egg stage took 18%, the first larval instar 13%, second instar 13%, third instar 35% and pupa 21% of the total development time. A poor diet increased the SET of the larvae. The results are compared with published data on Carabidae.

Developmental Rate Isomorphy in Insects and Mites

When the proportion of total developmental time spent in a particular developmental stage does not change with temperature, an organism shows "rate isomorphy." This is the case only if the lower developmental threshold is the same for all developmental stages. In this study, the incidence of rate isomorphy in seven species of mites and 342 species from 11 insect orders (some represented by several populations) was determined. Whether a species shows rate isomorphy or not was determined over a range of temperatures where the relationship between the rate of development and temperature is linear. Proportion of total developmental time spent in a particular stage was plotted against temperature and the existence of rate isomorphy inferred from a zero change in proportion. Rate isomorphy was detected in 243 (57%) of 426 populations. In the rest of the cases, rate isomorphy was violated by deviations in the proportion of time spent in a stage by an average of 0.2% (range 4.5E-06% to 2.8%) at the mean of the range of temperatures of all the data sets (11 degrees C). The violations occurred most frequently at the extremes of the linear phase, which is attributed to methodical biases, mortality at low temperatures, or too coarse an estimate of developmental time at high temperatures. Similarly, a meta-analysis also revealed an overall prevalence of rate isomorphy. Consequently, in insect and mite species, all the developmental stages appear to have the same population-specific lower developmental threshold. The existence of rate isomorphy could be of great practical importance, for example, in the timing of life-history events and in determining preadult thermal requirements. There are also indications that it may act as a phylogenetic constraint.