Impact of constant versus fluctuating temperatures on the development and life history parameters of Tetranychus urticae (Acari: Tetranychidae)

Modelling thermal reaction norms for development and viability in Drosophila suzukii under constant, fluctuating and field conditions

Phenological models for insect pests often rely on knowledge of thermal reaction norms. These may differ in shape depending on developmental thermal conditions (e.g. constant vs. fluctuating) and other factors such as life-stages. Here, we conducted an extensive comparative study of the thermal reaction norms for development and viability in the invasive fly, Drosophila suzukii, under constant and fluctuating thermal regimes. Flies, were submitted to 15 different constant temperatures (CT) ranging from 8 to 35 °C. We compared responses under CT with patterns observed under 15 different fluctuating temperature (FT) regimes. We tested several equations for thermal performance curves and compared various models to obtain thermal limits and degree-day estimations. To validate the model's predictions, the phenology was monitored in two artificial field-like conditions and two natural conditions in outdoor cages during spring and winter. Thermal reaction norm for viability from egg to pupa was broader than that from egg to adult. FT conditions yielded a broader thermal breadth for viability than CT, with a performance extended towards the colder side, consistent with our field observations in winter. Models resulting from both CT and FT conditions made accurate predictions of degree-day as long as the temperature remained within the linear part of the developmental rate curve. Under cold artificial and natural winter conditions, a model based on FT data made more accurate predictions. Model based on CT failed to predict adult's emergence in winter. We also document the first record of development and adult emergence throughout winter in D. suzukii. Population dynamics models in D. suzukii are all based on summer phenotype and CT. Accounting for variations between seasonal phenotypes, stages, and thermal conditions (CT vs. FT) could improve the predictive power of the models.

The influence of high-temperature frequency variation on the life-history traits of pyridaben-sensitive and -resistant strains of Tetranychus truncatus

With a generally warming global climate, the number of Tetranychus truncatus specimens in the Hexi region in China has been increasing. As ectotherms, the growth and development of T. truncatus are greatly affected by changes in environmental temperature. The effect of heatwaves on organisms depends on a delicate balance between damage and repair periods. Therefore, we simulated nine patterns of periodically recurring changes in the frequency of high-temperature days using an intraday gradual temperature change model to study and compare the effects on the development and reproduction of pyridaben-sensitive and -resistant strains of T. truncatus. The results showed that the influence of the frequency of high-temperature days on developmental stages, longevity and fecundity was different between the two strains. The egg and immature stages of the sensitive strain were all affected by hot days, whereas the adult stage was less affected by the frequency. The egg stage of the resistant strain was less affected; it was mainly affected in the immature and adult stages. Under the moderate condition of increasing the proportion of days at normal temperature, the longevity of the resistant strain gradually increased and reached a maximum at a 1:3 frequency, and then it decreased with the increase in high-temperature days. The longevity of the sensitive strain was less affected by frequency, and there was no significant difference between most treatment and control groups. In addition, both sensitive and resistant strains were able to complete growth and development under all nine frequencies of high-temperature days, but the reproductive rate was lower than it was at normal temperatures, indicating that both strains of T. truncatus adapted to high temperatures at the expense of reduced reproduction rates. This lays a key theoretical foundation for predicting the occurrence of agricultural pest populations under the background of climate warming and developing appropriate control strategies.

Influence of climate factors on population density and damage of the leopard moth, Zeuzera pyrina L., in walnut orchards, Iran

The effect of climate factors (temperature, humidity, precipitation, and frost days) on the population changes, damage, and infestation area of the leopard moth, Zeuzera pyrina L., was studied during 2006-2018 in four parts of Iran including Saman, Arak, Najaf-abad, and Baft. For trend analysis, the Mann-Kendall test was run on time series data of both climate and pest population. According to the results, the annual mean (Kendall's statistics, T = 0.64 and 0.48), annual minimum (T = 0.60 and 0.42), and January mean (T = 0.64 and 0.61, respectively) temperatures showed increasing trends in Saman and Najaf-abad. Moreover, the annual mean minimum and January temperatures (T = 0.41 and 0.45, respectively) in Arak and the annual mean maximum temperature (T = 0.79) in Baft showed increasing trends. The number of frost days/year (Kendall's statistics, T = -0.63, -0.53, -0.32 and -0.37) and annual mean relative humidity (T = -0.43, -0.63, -0.64 and -0.42, respectively) showed decreasing trends in Saman, Arak, Baft, and Najaf-abad stations. Trend analysis indicated significant increases in the mean number of moths caught (T = 0.59, 0.76 and 0.90), the percentage of infested branches/tree (T = 0.66, 0.58, and 0.90), the number of active holes/tree (T = 0.79, 0.55, and 0.68) and the infested areas (T = 0.99, 0.73, and 0.98, respectively) in Saman, Arak and Najaf-abad stations. According to stepwise regression, the mean temperatures of January, autumn, and winter were the most effective variables for increasing Z. pyrina damage and population, while relative humidity and the number of frost days played the major role in reducing it.

Population dynamics and molecular adaption of Tetranychus cinnabarinus to long-term thermal stress

BACKGROUND

Global warming is a general trend in the current era. Temperature is one of the most important nonbiological factors that affects the development, life cycle and distribution of arthropods, which are a major component of agriculture pests. This study focused on life-table parameters and the molecular adaption of Tetranychus cinnabarinus under long-term thermal stress.

RESULTS

The life tables of T. cinnabarinus were constructed at room temperature (26 °C) and high temperature (34 °C). Results showed that although the lifespan of the mites was shortened, the developmental periods of egg, larva and nymph stages were accelerated, and the peak egg-laying period came earlier at high temperature, which resulted in faster expansion of pest mite population. RNA-seq was used to reveal the thermal adaption mechanism according to differentially expressed genes. Combined with transcriptome data and quantitative polymerase chain reaction (qPCR) verification, MAPK, CAT, HSP20 and HSP70 were found highly expressed at 34 °C, which were associated with thermal adaption of T. cinnabarinus. RNAi analysis proved that expression of HSP20 was closely related to the survival of mites at high temperature.

CONCLUSION

These results indicated that long-term high temperature treatment was beneficial to the expansion of the T. cinnabarinus population. The genes involved in heat tolerance of T. cinnabarinus such as MAPK-HSP pathway provides ideas for subsequent control measures. © 2023 Society of Chemical Industry.

Parental exposure to heat waves improves offspring reproductive investment in Tetranychus urticae (Acari: Tetranychidae), but not in its predator, Phytoseiulus persimilis (Acari: Phytoseiidae)

The more frequent and intense occurrence of heat waves is a challenge for arthropods because their unpredictable incidence requires fast adaptations by the exposed individuals. Phenotypic plasticity within and across generations might be a solution to cope with the detrimental effects of heat waves, especially for fast-developing, small arthropods with limited dispersal abilities. Therefore, we studied whether severe heat may affect the reproduction of a pest species, the spider mite Tetranychus urticae, and its counterpart, the predatory mite Phytoseiulus persimilis. Single offspring females with different parental thermal origins (reared under mild or extreme heat waves) of both species were exposed to mild or extreme heat waves on bean leaves over 10 days, and the oviposition, egg sizes, survival, and escape behavior of the females were evaluated daily. The total losses of predators mainly via escapers were very high compared to prey, which makes a separation between selective and plastic effects on shifted reproductive traits impossible. Predator females laid smaller eggs, while their consumption and oviposition rates were unaffected during extreme heat waves. In comparison, larger prey females fed more and produced more, but smaller, eggs due to within- and trans-generational effects. These advantages for the prey in comparison to its predator when exposed to extreme heat waves during the reproductive phase support the trophic sensitivity hypothesis: higher trophic levels (i.e., the predator) are more sensitive to thermal stress than lower trophic levels (i.e., the prey). Furthermore, the species-specific responses may reflect their lifestyles. The proactive and mobile predator should be selected for behavioral thermoregulation under heat waves via spatiotemporal avoidance of heat-exposed locations rather than relying on physiological adaptations in contrast to the more sessile prey. Whether these findings also influence predator-prey interactions and their population dynamics under heat waves remains an open question.

Reproducing during Heat Waves: Influence of Juvenile and Adult Environment on Fecundity of a Pest Mite and Its Predator

The thermal history of arthropod predators and their prey may affect their reproductive performance during heat waves. Thus, a matching juvenile and adult environment should be beneficial as it enables the individuals to acclimate to extreme conditions. Prey fecundity, however, is also affected by a second stressor, namely predation risk. Here, we assessed the impact of extreme and mild heat waves on the reproductive output of acclimated (juvenile and adult heat wave conditions are matching) and non-acclimated females of the biocontrol agent Phytoseiulus persimilis, a predatory mite, and its herbivorous prey, the two-spotted spider mite Tetranychus urticae, on bean leaves. Their escape and oviposition rates and egg sizes were recorded over 10 days. Additionally, ovipositing prey females were exposed to predator cues and heat waves. Acclimation changed the escape rates and egg sizes of both species, whereas fecundity was only influenced by the adult thermal environment via increased egg numbers under extreme heat waves. Acclimation reduced predator and prey escape rates, which were higher for the predator. Pooled over acclimation, both species deposited more but smaller eggs under extreme heat waves. Acclimation dampened this effect in prey eggs, whereas acclimation resulted in smaller female eggs of the predator. Prey deposited larger male and female eggs. Predator cues reduced prey oviposition, but the effect was small compared to the large increase gained under extreme heat waves. We argue that the success of predators in controlling spider mites during heat waves mainly depends on the fates of escaping predators. A permanent absence of predators may result in the numerical dominance of prey.

Modeling Thermal Developmental Trajectories and Thermal Requirements of the Ladybird Stethorus gilvifrons

The development rate of the predatory ladybird, Stethorus gilvifrons (Mulsant), fed on Tetranychus urticae Koch, was determined at 15, 20, 25, 27, 30, 34, and 38 °C. The total development time from egg to adult emergence for females was estimated to be 61.4, 31.6, 14.4, 13.3, 12.5, and 11.7 days, respectively. The development time decreased with increasing temperature from 15 to 34 °C, but all eggs failed to hatch at 38 °C. The lower temperature threshold (T0) for the entire development period and the thermal constant (K) for female S. gilvifrons were estimated to be 11.64 °C and 194.50 degree-days (DD) using the common linear model, and 11.96 °C and 187.87 DD using the Ikemoto and Takai model, respectively. Data were fitted to 20 non-linear development rate models and the thermal thresholds (Tmin and Tmax) and optimal temperature (Topt) were estimated. Among non-linear models, the Briere-2 and Ikemoto and Takai linear model provided adequate descriptions of the temperature-dependent development of S. gilvifrons. The upper-temperature threshold was estimated to be about 44 °C using the Logan-10 non-linear model. The estimated thermal development characteristics can be used to predict the occurrence and the population dynamics, as well as to improve the mass rearing and release, of S. gilvifrons for the biological control of T. urticae.

Development and Reproductive Capacity of the Miyake Spider Mite Eotetranychus kankitus (Acari: Tetranychidae) at Different Temperatures

Eotetranychus kankitus (Acari: Tetranychidae) is an important pest of citrus. Assessing life history parameters is crucial to developing an ecologically sound pest management program. Of the many factors that affect life history parameters of herbivorous insects and mites, temperature has the greatest influence on development rate and reproductive potential. We investigated the effects of temperatures from 15 to 40 °C on the demographic parameters of E. kankitus under a long-day (16:8 (L:D) h) photoperiod. The egg-to-adult development time of E. kankitus decreased as the temperature increased from 15 to 32.5 °C. At 35 °C, the female laid eggs that died at the larval stage. The estimated lower thermal thresholds (t₀) were 11.01 and 10.48 °C, and the thermal constants (K) were 190.67 and 188.63 degree-days for egg-to-adult females and egg-to-adult males, respectively. The intrinsic optimal temperatures (T_Ø) for development were 21.79 and 21.74 °C, respectively. The bootstrap-match technique was used in the construction of the life table paramaters. The net reproductive rate (R₀) decreased as temperature increased from 20 to 30 °C, but the lowest rate was observed at 15 °C. The intrinsic rate of natural increase (r) increased from 0.0299 day^-1 at 15 °C to 0.1822 day^-1 at 30 °C. These findings provide a critical theoretical basis for predicting the occurrence of E. kankitus populations under climate warming and for developing appropriate control strategies.

Frequency of Temperature Fluctuations Subtly Impacts the Life Histories of a Tropical Snail

AbstractMost organisms are faced with daily cyclic changes in a suite of environmental conditions, including temperature. In shallow marine waters, populations of the same species may experience either intertidal or subtidal conditions, such that some individuals experience extreme daily fluctuations as the tide ebbs and flows, while others only a few meters away experience less pronounced or less frequent fluctuations or almost constant thermal conditions. This study used a fully factorial combination of three thermal treatments and two diet treatments to test the hypotheses that (1) individuals experiencing fluctuating temperatures perform more poorly than those experiencing the same mean temperature under constant conditions and that (2) the negative impact of fluctuating temperatures is greater under food-limiting conditions. Five life-history components of the slipper snail Crepidula cf. marginalis were used as response variables. We found that temperature fluctuations impacted size at hatching and time to hatching, as well as growth rate, to some extent. Diet treatments impacted growth rates, clutch sizes, time to first brood, and time to hatching. There were no statistically significant interactions between the two factors. These results show that fluctuations between two temperatures that are typically experienced by these animals in the field can significantly affect fitness-related characters and, therefore, suggest the tidal height at which larvae settle can significantly impact individual fitness. This is one of the first studies to demonstrate that differences in the frequency of fluctuations, in the absence of differences in the magnitude or the mean, can have significant impacts on invertebrate life histories.

Heat waves affect prey and predators differently via developmental plasticity: who may benefit most from global warming?

BACKGROUND

Climate warming is considered to affect the characteristics of heat waves by increasing their duration, frequency and intensity, which can have dramatic consequences for ectothermic arthropods. However, arthropods may respond to heat waves via plastic modifications, which could differently affect a predator and its prey. We examined this assumption using prominent counterparts in biological control, the predatory mite Phytoseiulus persimilis and its prey, the spider mite Tetranychus urticae. Individuals of both species were separately exposed to mild and extreme heat waves during their juvenile development.

RESULTS

Both species developed faster during extreme heat waves, but the proportional increase of the developmental rates was higher in the prey. Independent of sex, P. persimilis reached smaller size at maturity under extreme heat waves, whereas the body size modifications were sex-dependent in T. urticae: males became smaller, but females were able to maintain their size.

CONCLUSIONS

An accelerated development may result in the reduction of the exposure time of susceptible juvenile stages to heat waves and prey stages to predators. Plastic size adjustments caused a shift in the female predator-prey body size ratio in favor of the prey, which may lead to higher heat resistance and reduced predation risk for prey females under extreme heat waves. In conclusion, our findings indicate that species-specific shifts in age and size at maturity may result in lower suppression efficacy of the predator P. persimilis against its prey T. urticae with severe consequences for biological control of spider mites, if global warming continues.

Evaluation of the Impact of Different Management Methods on Tetranychus urticae (Acari: Tetranychidae) and Their Predators in Citrus Orchards

To evaluate the effectiveness of eco-friendly treatments based on detergents classified as non-hazardous and black soap on the pest Tetranychus urticae Koch 1836, and their predators (Euseius stipulatus Athias-Henriot, 1960, Typhlodromus sp., Phytoseiulus persimilis Athias-Henriot, 1957), different treatments were applied to citrus orchards planted with Valencia late (Orange) in the Mechraa Belksiri region of Morocco (T0 = control experiment; T1 = spirodiclofen 0.5 L/Ha; T2 = 125 L/Ha (5%) of black soap; T3 = detergent; 4 L/Ha of Oni product + 2 L/Ha of Tide product). The results obtained during the whole monitoring period indicated that the three treatments used, namely spirodiclofen, black soap, and detergents, ensured a reduction in the rate of population of the pest T. urticae compared to the untreated plot. In the untreated plot, the average was 45.01 A± 4.90 mobile forms, while the plot treated with spirodiclofen it was only 21.10 C ± 2.71, the black soap 31.49 B ± 3.35, and in the plot treated with detergents, the average was similar to that obtained by spirodiclofen (22.90 C ± 2.18). On the predators (E. stipulatus, P. persimilis, and Typhlodropmus sp.), the black soap and the treatment with detergents were less harmful compared to the chemical spirodiclofen.

Effects of Constant versus Fluctuating Temperatures on Fitness Indicators of the Aphid Dysaphis plantaginea and the Parasitoid Aphidius matricariae

Simple Summary

Like all organisms, insects encounter temperatures that fluctuate on different time scales: within a day, between days, or throughout the seasons. However, most studies on the impact of temperature on insect physiology, behavior, morphology, or ecology have focused on constant temperatures tested in the laboratory. In our study, we wanted to know if fluctuating temperatures during the day (7–17 °C, average 12 °C) can affect insects differently compared to a constant temperature of 12 °C. We used, as a model, the apple aphid Dysaphis plantaginea, a major threat to apple orchards worldwide, and its parasitoid Aphidius matricariae, which is used in biological control. We found that many traits—but not all—were affected. In particular, the fluctuating thermal regime reduced the development time of aphids and parasitoids, improved the rate of parasitism, and tended (albeit slightly) to increase the longevity of both species. In contrast, we did not find strong effects on morphological traits. Our results can be used to better predict how these agronomically important insects behave in orchards, how ecologically-relevant fluctuating temperatures affect host–parasitoid relationships, and ultimately what the implications are in the context of climate change and biological control.

Abstract

Testing fluctuating rather than constant temperatures is likely to produce more realistic datasets, as they are ecologically more similar to what arthropods experience in nature. In this study, we evaluated the impact of three constant thermal regimes (7, 12, and 17 °C) and one fluctuating thermal regime (7–17 °C with a mean of 12 °C) on fitness indicators in the rosy apple aphid Dysaphis plantaginea, a major pest of apple orchards, and the parasitoid Aphidius matricariae, one of its natural enemies used in mass release biological control strategies. For some—but not all—traits, the fluctuating 7–17 °C regime was beneficial to insects compared to the constant 12 °C regime. Both aphid and parasitoid development times were shortened under the fluctuating regime, and there was a clear trend towards an increased longevity under the fluctuating regime. The fecundity, mass, and size were affected by the mean temperature, but only the mass of aphids was higher at 7–17 °C than at a constant 12 °C. Parasitism rates, but not emergence rates, were higher under the fluctuating regime than under the constant 12 °C regime. Results are discussed within the framework of insect thermal ecology and Jensen’s inequality. We conclude that incorporating thermal fluctuations in ecological studies could allow for the more accurate consideration of how temperature affects host–parasitoid interactions and insect responses to temperature change over time.

Sex dimorphism of life-history traits and their response to environmental factors in spider mites

Sex dimorphism is ubiquitous in the animal kingdom and can be influenced by environmental factors. However, relatively little is known about how the degree and direction of sex difference vary with environmental factors, including food quality and temperature. With the spider mites from the family Tetranychidae as subjects, the sex difference of life-history traits in responses to host plant and temperature were determined in this meta-analytic review. Across the 42 studies on 26 spider mite species (N = 8057 and 3922 for female and male mites, respectively), female spider mites showed longer developmental duration than the males in all except two species. The direction of sex difference in development was consistent regardless of temperature and host plant. The 16 spider mite species in 33 studies generally showed female-biased longevity, with an overall effect size of 0.6043 [95%CI = 0.4054-0.8031]. Host plant significantly influenced the sex difference in longevity, where the males lived longer than females below 22.5 ℃, but the reverse was true at higher and fluctuating temperature. Host plant also influenced the magnitude of sex difference in longevity, with females living longer than males when reared on herbs but not on trees. This study indicated that life-history traits are highly variable between sexes under temperature and host plant influence, highlighting that environmental conditions can significantly shape the direction and magnitude of sexual dimorphism of life-history traits.

Impact of Constant and Fluctuating Temperatures on Population Characteristics of Tetranychus pacificus (Acari: Tetranychidae)

To understand the effect of fluctuating temperature on the population characteristics of Tetranychus pacificus, we determined their life tables under constant temperatures between 10 and 35°C and fluctuating temperatures (12 h per day at each of 5°C above and 5°C below the corresponding constant temperature). Tetranychus pacificus eggs did not hatch when held at a constant temperature of 10°C, whereas 77.6% of the T. pacificus eggs reached an adult life stage at fluctuating temperature 10°C ± 5°C. Female preadult development was faster under fluctuating temperatures 12.5, 15, and 20°C than under constant temperatures, whereas it was not significantly different at temperatures ≥ 22.5°C. The lower developmental thresholds (T0) for female preadult development were 10.24 and 5.73°C for the constant and fluctuating temperatures, respectively, while the thermal summations (K) were 215.10 and 265.64 degree days, respectively. The net reproductive rates (R0) at constant temperatures 15 and 35°C were significantly higher than those at the corresponding fluctuating temperatures. However, for 20, 25, and 30°C, the R0 values were not significantly different between constant and fluctuating temperatures. The intrinsic rate of increase (r) and finite rate of increase (λ) at fluctuating temperatures 10, 20, and 30°C were higher compared to the corresponding constant temperature. However, the values of r and λ at constant 25 and 35°C were higher than those at fluctuating temperature. The differential responses of life history between constant and fluctuating temperatures help to understand the population dynamics of T. pacificus under natural conditions.

Effects of Temperature on Demographic Parameters of Bryobia praetiosa (Acari: Tetranychidae)

The clover mite, Bryobia praetiosa Koch (Acari: Tetranychidae), is an agricultural pest, as well as a frequent invader of hospitals and homes. However, its adaptability to different temperatures is not well understood. We used age- and stage-specific life tables to investigate the effects of temperature on demographic parameters of B. praetiosa from 15 to 35°C under a long-day photoperiod (16:8 [L:D] h). The clover mite is a thelytokous species (consisting of only females) due to its infection with the symbiotic bacterium Wolbachia. The egg-to-adult development time of female B. praetiosa decreased as the temperature increased from 15 to 32.5°C. At 35°C, females laid eggs, but no eggs hatched. The lower thermal threshold (t0) and the thermal constant (K) for egg-to-adult females were 8.7°C and 274.1 degree-days, respectively. The intrinsic optimum temperature (TØ) was 22.4°C. The oviposition period decreased with increasing temperature. Fecundity was highest at 20°C and extremely low at 30°C. The net reproductive rate (R0) decreased as the temperature increased from 15 to 30°C, but no significant difference was observed between 15 and 20°C. The intrinsic rate of natural increase (r) varied from 0.0721/d at 15°C to 0.1679/d at 25°C, and then decreased to 0.1203/d at 30°C. These results should be useful in developing management strategies for B. praetiosa.

Seasonal occurrence and development of three closely related Oligonychus species (Acari: Tetranychidae) and their associated natural enemies on fagaceous trees

We compared the life cycles and diapause attributes among three closely related spider mites, Oligonychus castaneae on Castanea crenata, and O. gotohi and O. amiensis on Lithocarpus edulis. The lower thermal thresholds from egg to egg were 10.5, 8.5 and 8.9 °C, respectively, and the thermal constants were 177.8, 229.5 and 232.5 degree-days, respectively. The cumulative hatching rates of diapause eggs of O. castaneae and O. gotohi increased as the season progressed in and after early-to-mid January, which indicates diapause termination. In contrast, O. amiensis showed higher hatching rates in December and January, but hatchability gradually decreased in and after February because some of the eggs died from the cold. Oligonychus castaneae and O. gotohi females produced diapause eggs in response to the short photoperiod in late September to early October and in early-to-late October, respectively, which corresponded to the times predicted by the critical photoperiods (at 15 °C) of 12 h 15 min and 11 h 15 min for the respective species. Oligonychus castaneae showed at least a single population peak over the 3-year observation period, but the time of peak population varied from mid-July to mid-September. The population of O. gotohi was higher between November and May when diapause eggs were present on host plants in early winter and the first-generation females laid eggs on leaves in spring. The population of O. amiensis, which is a non-diapause species, was only high between September and December, because eggs were laid on leaves in autumn to winter and then gradually disappeared and/or died during winter. Natural enemies were observed as the number of spider mites declined, and the density suppression effect by natural enemies was confirmed in the field.

Population performance of Tetranychus evansi (Acari: Tetranychidae) on African tomato varieties and wild tomato genotypes

The tomato red spider mite, Tetranychus evansi Baker & Pritchard, is one of the main pests of the tomato crop in several countries, mainly in Africa, where it can reduce tomato yield by up to 90%. The biotic potential of this mite is high and its control is difficult because of low efficiency of chemicals used and the rapid development of resistance to acaricides. We used the two-sex life table to evaluate the effect of two wild tomato genotypes (PI134417 and PI134418) and five tomato varieties widely grown in Benin (Kekefo, Akikon, TLCV15, Tounvi, and TOML4) on demographic characteristics of T. evansi under laboratory conditions. Tetranychus evansi did not develop on the genotypes PI134417 and PI134418, indicating their resistance to this mite. Developmental time of immature stages and female longevity were significantly higher on TLCV15 and Kekefo. Fecundity, net reproductive rate (R₀), intrinsic rate of increase (r), and finite rate of increase (λ) of T. evansi on the African varieties were not statistically different among varieties. Generation time (T) was shorter on TOML4 than on TLCV15 and Tounvi. Thus, efforts should be made to prospect varieties with resistance characteristics or to develop other control means, to reduce the use of pesticides to control T. evansi in Africa.

Demographic Comparison of the Tetranychus urticae Koch. (Acari: Tetranychidae) Reared on Different Cultivars of Strawberry

The twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is an important pest of strawberry (Fragaria × ananassa Duch.) grown in greenhouses and outdoors. In this study, we evaluated the resistance status of five common strawberry cultivars ('Aromas', 'Kurdistan', 'Missionary', 'Paros', and 'Queen Elisa') under laboratory conditions. The developmental times of the preadult and adult stages, total longevity, reproduction, and life table parameters were analyzed according to the age-stage, two-sex life table theory, which provides the most comprehensive description on the survival, stage differentiation, and reproduction of a population. Preadult development was the shortest on Kurdistan and longest on Aromas (17.70 d vs. 21.00 d). The greatest number of oviposition days occurred on Missionary (28.65 d), whereas the fewest were on Queen Elisa (21.58 d). The intrinsic rate of natural increase (r) and finite rate of increase (λ) varied among the cultivars. The highest values were found on Kurdistan (r = 0.1436d-1, λ=1.1544d-1), while the lowest values were on the Aromas cultivar (r = 0.1081d-1, λ=1.1141d-1). The longest mean generation time (T) of T. urticae occurred on Aromas. Based on the results of the present study, the cultivar Aromas was considered the most resistant to T. urticae and least favored strawberry cultivar for the development and reproduction of the mite. Demographic data of twospotted spider mite on these five strawberry cultivars can be used to improve our understanding of the population dynamics of the pest and thereby develop effective pest management strategies against T. urticae in both integrated and organic strawberry production.

Mathematical modeling of climate change and malaria transmission dynamics: a historical review

Malaria, one of the greatest historical killers of mankind, continues to claim around half a million lives annually, with almost all deaths occurring in children under the age of five living in tropical Africa. The range of this disease is limited by climate to the warmer regions of the globe, and so anthropogenic global warming (and climate change more broadly) now threatens to alter the geographic area for potential malaria transmission, as both the Plasmodium malaria parasite and Anopheles mosquito vector have highly temperature-dependent lifecycles, while the aquatic immature Anopheles habitats are also strongly dependent upon rainfall and local hydrodynamics. A wide variety of process-based (or mechanistic) mathematical models have thus been proposed for the complex, highly nonlinear weather-driven Anopheles lifecycle and malaria transmission dynamics, but have reached somewhat disparate conclusions as to optimum temperatures for transmission, and the possible effect of increasing temperatures upon (potential) malaria distribution, with some projecting a large increase in the area at risk for malaria, but others predicting primarily a shift in the disease's geographic range. More generally, both global and local environmental changes drove the initial emergence of P. falciparum as a major human pathogen in tropical Africa some 10,000 years ago, and the disease has a long and deep history through the present. It is the goal of this paper to review major aspects of malaria biology, methods for formalizing these into mathematical forms, uncertainties and controversies in proper modeling methodology, and to provide a timeline of some major modeling efforts from the classical works of Sir Ronald Ross and George Macdonald through recent climate-focused modeling studies. Finally, we attempt to place such mathematical work within a broader historical context for the "million-murdering Death" of malaria.