Developmental Threshold Research Articles

Influence of temperature on the development and reproduction of Cinara cedri (Hemiptera: Aphidoidea: Lachninae).

Temperature is one of the main factors affecting insect growth, development and reproduction. The effects of temperatures (10, 15, 20, 25 and 30°C) on the development and reproduction of Cinara cedri Mimeur (Hemiptera: Aphidoidea: Lachnidae) fed on Cedrus deodara (Roxb.) G. Don were evaluated in this study. With the increase of temperature from 10 to 30°C, the development duration at different development stages gradually shortened. There was a significant positive correlation between the developmental rates and temperature, following a quadratic regression model. The lower developmental threshold temperature (C) and effective accumulated temperatures (K) for completing a generation were 4.13°C and 263.4 degree-days, respectively. The highest fecundity was observed at 20°C with 25.74 first-instar nymphs/female. Both the highest intrinsic rate of increase (r, 0.11 ± 0.03) and net reproduction rate (R0, 19.06 ± 2.05) were observed at 20°C, whereas the lowest values of r (0.05 ± 0.01) at 10°C and R0 (5.78 ± 0.88) at 30°C were observed. The results suggest that temperature significantly affects the biology of C. cedri and the optimal temperature for its development is 20°C.

Validation of a new method for measuring oxygen consumption in insects

Oxygen consumption is difficult to measure in small insects and those with very low metabolic rates, such as insects undergoing diapause or during exposure to low temperatures. One method that works well is the use of closed system respirometry. In this study, we validated the Loligo Systems microplate system for measuring individual respiration in air using the alfalfa leafcutting bee, Megachile rotundata. The Loligo system is a closed system that uses optical fluorescence and was designed for use with aquatic systems, with few studies in insects. We placed overwintering, pre-pupal bees in 29°C to initiate metamorphosis. After 2 weeks, bees were placed in 6, 10, 14, 18, 22, 26, 29, 33, or 35°C, and metabolic rate was measured using the microplate system. Bees (n = 32 for each temperature) were placed into one well of the 24 well-plate and oxygen consumption was measured for 3 hours. We also compared pupal bees dissected from brood cells to those that were undisturbed. Not surprisingly, oxygen consumption increased with temperature. Interestingly, there appeared to be a breakpoint around 18°C, which is the developmental threshold for M. rotundata. Bees remaining in the brood cells had metabolic rates that were not different from those that had been excised. Not only does this system allow for measuring low respiration rates, it opens the possibility of reducing abiotic stressors incurred during oxygen consumption measurements, including the low humidity required for most measurement devices and, in the case of M. rotundata, the need to remove the developing insect from its protective cocoon.

Population growth and development of the psocid Liposcelis obscura (Psocodea: Liposcelididae) at constant temperatures and relative humidities

The effects of nine temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, 40.0, and 42.5 °C) and four relative humidities (RHs; 43, 55, 63, and 75%) on the population growth and development of the parthenogenetic Liposcelis obscura Broadhead (Psocodea: Liposcelididae) were investigated in laboratory studies. Results showed that L. obscura did not survive at 43% RH at all temperatures tested. At 55% RH, L. obscura survived at 22.5, 25, and 27.5 °C; none survived at 42.5 °C and ≤63% RH. Population growth was highest at 40.0 °C and 75% RH, where population increase was 216-fold from an initial population of five adult females. Liposcelis obscura has three-to-five nymphal instars, and the percentages of individuals with three, four, and five instars were 52, 41, and 7%, respectively. Temperature-dependent developmental equations were developed for L. obscura eggs, individual nymphal, combined nymphal, and combined immature stages. Liposcelis obscura populations grew much faster at 30–42.5 °C and 75% RH. Based on the equation for total developmental time, the predicted optimal development temperature is 39.2 °C and development was completed in 14.0 d. The upper developmental threshold was estimated as 47.1 °C. The lower developmental threshold was estimated as 14.7 °C. These data provide a better understanding of L. obscura population dynamics and can be used to develop effective management strategies for this psocid.

Effect of temperature on some biological aspects and the thermal requirements of Diaeretiella rapae (M'Intosh) (Hymenoptera:Braconidae) reared on Rhopalosiphum padi L. (Homoptera: Aphididae)

Developmental periods, adult longevity and thermal requirements of Diaeretiella rapae (M'Intosh) were investigated at 18, 20, 22 and 24°C constant temperature. The development durations decreased as the temperature increased. At 24°C and 18°C the periods for egg-mummy period was 8.85 days and 12.79 days; the mummy-adult period was 5.29 days and 7.31 days; the egg-adult period was 14.14 days and 20.10 days; and for the adult longevity was 3.22 days and 4.69 days. The rate of development of all stages increased as the temperature increased from 18 to 24°C. The developmental threshold of D. rapae estimated using linear regression was 4.5, 2.33, 3.75 and 4.87, while the mean thermal units were 166.8, 117.03, 282.53 and 64.51 for egg-mummy period, mummy-adult period, egg-adult period and adult longevity, respectively. Results revealed that the optimal temperature for growth population of D. rapae ranged from 18 to 20°C. Key words: Diaeretiella rapae, Rhopalosiphum padi, biological aspects, Temperatures

Why do nestling birds fledge early in the day?

In altricial birds, leaving the nest is a key life history transition associated with a high risk of mortality. Studies of numerous species have shown that young typically fledge early in the day, and it is often asserted that early fledging is important for survival; however, evidence for this hypothesis is limited. We used an automated monitoring system to obtain precise fledging times of 1582 young blue tits, Cyanistes caeruleus , from 230 nests. As expected, nestlings primarily fledged early in the day (84% fledged before midday). However, we found no evidence that early fledging was associated with higher postfledging survival (i.e. recorded the following autumn or later). We propose two alternative explanations for the morning peak in fledging. Hypothesis 1 is that some offspring reach a developmental threshold for fledging overnight and leave the nest early the next day. This is supported by our observation that offspring that fledged early in the day tended to be more developed than those that fledged later in the day, that is, they were older and had a high body mass (measured at 14 days of age) for their fledging age. Hypothesis 2 is that the timing of fledging is related to parental provisioning behaviour. Our results do not support this hypothesis. Parents reduced their nest visit rate over the course of the day, but offspring did not fledge earlier when their parents decreased their visit rate more strongly with time of day. In conclusion, our results do not support the notion that the time of fledging affects survival but suggest a link with nestling development. • In altricial birds, nestlings typically fledge early in the day. • This is often assumed to improve survival, but with little supporting evidence. • We monitored the precise fledging times of 1582 blue tits from 230 nests. • Fledging time was not associated with the probability of local survival. • Instead, fledging time was related to the developmental stage of nestlings.

Interactive effect of photoperiod and temperature on the induction and termination of embryonic diapause in the migratory locust.

Diapause plays a vital role in the survival and population reproduction of the migratory locust in temperate regions. Although some studies have suggested that photoperiod and temperature are two important environmental factors involved in the induction and termination of embryonic diapause in locusts, the independent or synergetic roles of these two factors are still unclear. We designed crossover experiments to investigate the effects of photoperiod, temperature and treatment time on the induction and termination of embryonic diapause in locusts by optical coherence tomography (OCT), which can track the entire embryonic developmental process via noninvasive 3D real-time imaging. Diapause induction experiments showed that a short photoperiod (in adults) and a low egg treatment temperature are the most important prerequisites for inducing egg diapause. The diapause rate reached 90.7% when the adults were reared under a short photoperiod (8 L:16 D) and the eggs were treated at 22 °C. However, the adult rearing temperature had no significant effect on diapause induction. Analysis of variance also confirmed that there was a significant interactive effect between parental photoperiod and egg treatment temperature. Moreover, diapause termination experiments showed that 13 °C (near the developmental threshold temperature of 15 °C) for 20 days is the most effective condition for terminating diapause. Our study provides accurate photoperiod and temperature thresholds for inducing and terminating diapause in the migratory locust, suggesting potential applications in the prediction and control of locust plagues. © 2021 Society of Chemical Industry.

Biological traits of the predatory mirid Macrolophus praeclarus, a candidate biocontrol agent for the Neotropical region.

The predatory mirid Macrolophus praeclarus is widely distributed throughout the Americas, and is reported to prey upon several horticultural pest species. However, little is known about its biology, thermal requirements, crop odour preferences, phytophagy, and capability to induce defensive responses in plants. When five temperatures studied (20, 25, 30, 33 and 35°C) were tested and Ephestia kuehniella was used as prey, the developmental time from egg to adult on tomato, was longest at 20°C (56.3 d) and shortest at 33°C (22.7 d). The ability of nymphs to develop to adults decreased as the temperature increased, with the highest number of nymphs reaching the adult stage at 20°C (78.0%) and lowest at 35°C (0%). The lower and upper developmental thresholds were estimated at 11.2° and 35.3°C, respectively. The maximum developmental rate occurred at 31.7°C and the thermal constant was 454.0 ± 8.1 degree days. The highest predation rate of E. kuehniella eggs was obtained at 30°C. In Y-tube olfactory choice tests, M. praeclarus selected tomato, sweet pepper and eggplant odours more frequently than no plant control treatment. Macrolophus praeclarus feeding did not damage tomato plants compared to another zoophytophagous mirid, Nesidiocoris tenuis, which caused necrotic rings. The phytophagy of M. praeclarus induced defensive responses in tomato plants through the upregulation of the jasmonic acid metabolic pathway. The implications of the findings for using M. praeclarus in tomato biological control programmes in the Americas are discussed.

Spatial analysis of changes in Plodia interpunctella (Lepidoptera: Pyralidae) distribution depending on diets

Plodia interpunctella is a globally important insect pest that infests stored food products. Infestation may cause a substantial increase in economic costs for pest control and entails quality loss and dissatisfaction of consumers. The aim of this study was to predict the potential distribution of P. interpunctella feeding on four different diets (rice bran, vegetables, wheat bran, or walnuts) using a CLIMEX model and provide basic data for the storage and management of processed food products. To estimate the CLIMEX parameter of P. interpunctella feeding on rice bran, the developmental rate at different temperatures was tested, resulting in a lower developmental threshold and the degree days of 12.5 °C and 461 DD, respectively. In the spatial analysis, the climatic suitability of P. interpunctella feeding on rice bran was the highest when compared to other diets and particularly higher than that of walnuts in 23.3% of the total area. Our results are expected to provide basic data for the management of P. interpunctella based on species distribution modeling, which, in our study, produced different predicted distribution patterns based on diet and climate.

The evolution of developmental thresholds and reaction norms for age and size at maturity

Developing organisms typically mature earlier and at larger sizes in favorable growth conditions, while in rarer cases, maturity is delayed. The rarer reaction norm is easily accommodated by general life history models, whereas the common pattern is not. Theory suggests that a solution to this paradox lies in the existence of critical size thresholds at which maturation or metamorphosis can commence, and in the evolution of these threshold sizes in response to environmental variation. For example, ephemeral environments might favor the evolution of smaller thresholds, enabling earlier maturation. The threshold model makes two unique and untested predictions. First, reaction norms for age and size should steepen, and even change sign, with decreases in threshold size; second, food reductions at sizes below the threshold should delay maturation, while those occurring after the threshold should accelerate maturation. We test these predictions through food manipulations in five damselfly species that theory suggests should differ in threshold size. The results provide strong support for the threshold model's predictions. In all species, early food reductions delayed maturation, while late reductions accelerated maturation. Reaction norms were steeper, and the effect of food reductions changed from decelerating to accelerating at a much smaller size in species from ephemeral habitats. These results support the view that developmental thresholds can account for the widespread observation of negative correlations between age and size at maturity. Moreover, evolution of the threshold appears to be both predictable and central to the observed diversity of reaction norms for age and size at maturity.

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.

Rethinking our Work with Leaders: Using Developmental Threshold Zones in Coaching

The current paper brings together three bodies of work, each of which contributes to a new approach to learning and development, and identifies three elements that can be used with leaders in coaching: security, stories, and scaffolding. In particular, it looks at how Developmental Threshold Zones (Drake, 2018a) can be used to enrich the coaching process and outcomes with leaders. The first section explores attachment theory and its contribution to understanding how leaders secure themselves relationally. The second section explores narrative coaching and its contribution to understanding how leaders develop and move through change. The third section explores Vygotsky's (1934/1987, 1978) work on zones of proximal development and its contribution to our understanding of the scaffolding leaders need into order to grow. Each section contributes to the our understanding of how to use Developmental Threshold Zones (DTZs) and how it can be used in coaching to facilitate transformative experiences for leaders using their own stories.

Temperature impact on the phenology of Nesidiocoris tenuis feeding on Tetranychus urticae: simulation through life cycle modelling

Climatic factors especially temperature has direct impact on the survival of insects. The mirid bug Nesidiocoris tenuis Reuter is an important predator of whiteflies, leafminers, thrips, mites, and various lepidopterans. The impact of temperature on population parameters of N. tenuis was studied by developing model. The rearing temperature had significant impact on the development of N. tenuis. The development time of each nymphal stage decreased with the increase in rearing temperature. The rate of development for each stage increased linearly with the increase in temperature. The optimum temperature, lower and upper developmental thresholds for immature development of the bug varied from 29.9–33.28, 10.1 to 12.25 and 38.82 to 41.1 °C, respectively. The fertility statistics generated for N. tenuis reared on Tetranychus urticae Koch at different temperatures indicate that temperature between 20 and 35 °C is suitable for population growth and multiplication of the bug, whereas, low temperature (15 °C or below) is not suitable for the same. The present study, however, provides useful information on the impact of temperature on the development, survival, reproduction and life-fertility parameters of N. tenuis which could be used for spatial mapping of the distribution and abundance of the bug, and its possible utilization as bio-control agent under expected climate change.

Photoperiodic induction of reproductive diapause and life-history traits of a tortoise beetle, Laccoptera nepalensis (Coleoptera: Chrysomelidae), a range-expanding pest of southern origin

The tortoise beetle, Laccoptera nepalensis Boheman (Coleoptera: Chrysomelidae), is an important insect pest of the sweet potato, and is naturally distributed in southern to eastern Asia. The species has recently been expanding its range to the main islands of Japan, where it had previously not been distributed. In this study, the life-history traits of a local population in southern Kyushu, Japan were examined. The adults showed a long-day photoperiodic response at 20 and 25 °C with critical photophases of 13.97 and 12.52 h/day, respectively: female adults reared under long-day conditions laid eggs, whereas those reared under short-day conditions did not and entered diapause. When adults that had been reared under 16L–8D at 20 °C were transferred to 12L–12D at 20 °C, they ceased laying eggs. These results, together with the developmental threshold temperature and thermal constant obtained for each stage, suggest that the beetle overwinters in the adult stage in a state of diapause and produces a maximum of three generations per year in southern Kyushu.

Development and survival of brinjal shoot and fruit borer Leucinodes orbonalis Guenee (Crambidae: Lepidoptera) at constant and alternating temperatures

Brinjal shoot and fruit borer (BSFB) Leucinodes orbonalis Guenee is a key pest of brinjal and a major constraint to its production in the Indian subcontinent. The influence of constant as well as alternating temperatures on the development and survival of the pest is not known. Also, no information is available on the thermal constant, development thresholds, and phenology for the insect. So, the development and survival of Leucinodes orbonalis were studied under laboratory conditions at five constant (15 ± 1, 20 ± 1, 25 ± 1, 30 ± 1 and 35 ± 1 °C) and six alternating temperatures (25:15, 30:15, 35:15, 25:20, 30:20 and 35:20 °C) with 70 ± 5% R.H. and photoperiod of 14:10 (L:D) h. Under the alternating temperature regimes, maximum and minimum temperatures were maintained in a cycle of 14 and 10 h, respectively. Transition from maximum to minimum temperature followed square waveform and was complete within 10 min. The rate of development of the egg, larval, pupal, and adult stages accelerated with increases in the levels of temperature. Survival of BSFB was highest at intermediate temperature levels (25-30 °C), and it started declining outside this range. The favourable range of constant temperature for the development from egg to adult stage was 20 ± 1–35 ± 1 °C, while all six alternating temperatures were conducive for complete development of the pest. The thermal constant (K) and lower developmental threshold (Tmin) determined from a linear regression analysis for the total development period were 435.39–530.66 DD and 5.69–14.63 °C, respectively. The non-linear models did not fit the data obtained from constant temperature studies, as they overestimated the temperature threshold for the pest. In the case of alternating temperatures, Tmin, Topt, and Tmax for the different developmental stages were in the range of 6.87–10.47 °C, 30.3–30.4 °C, and 41.96–42.31 °C, under Briere-1, Briere-2 and Kontodimas models. Our results provide a framework for forecasting the pest incidence in the field, thus helping in modulating management schedules and techniques to target the weak link in the life cycle of the pest.

Comparison of the Hatch of Newly Laid Lycorma delicatula (Hemiptera: Fulgoridae) Eggs From the United States After Exposure to Different Temperatures and Durations of Low Temperature.

Comparisons were made of the effects of temperature and duration of low temperature on hatch of newly laid egg masses of the invasive spotted lanternfly, Lycorma delicatula (White). Egg masses were collected in mid-October 2019 and estimated to be less than 14 d old. There was a significant positive nonlinear relationship between temperature and developmental rate (1/d) for eggs held at constant temperatures. The lower threshold for egg development was estimated as 7.39°C. Eggs held at constant 10, 15, and 20°C were estimated to require 635, 715, and 849 DD7.39, respectively, to develop. Egg hatch was variable, egg hatch rates were highest (58.4%) when held at a constant 15°C, though high rates (52.7%) were also obtained when eggs were held for 84 d at 10°C, then moved to 25°C. Almost all eggs enter diapause since very few eggs were able hatch when moved to 25°C after 7 d of chill at either 5 or 10°C. Chilling at 5 or 10°C increased percentage egg hatch as the duration in chill increased up to ~100 d and eggs held at 10°C were able to complete some or all the post-diapause development before being moved to 25°C. All egg masses were held at constant 16:8 (L:D) photoperiod and 65%RH. Our data suggest that temperature is the driving factor for diapause termination in spotted lanternfly, but other abiotic factors should be investigated. These identified developmental temperature threshold and degree day requirements for egg hatch will improve predictive distribution and phenological models.

Effects of Temperature on Development and Survival of Nymphal Lycorma delicatula (Hemiptera: Fulgoridae).

Lycorma delicatula (White), an invasive planthopper originally from Asia, is an emerging pest in North America. It is important to understand its phenology in order to determine its potential range in the United States. Lycorma delicatula nymphs were reared on Ailanthus altissima (Miller) (Sapindales: Simaroubaceae) at each of the following constant temperatures: 5, 10, 15, 20, 25, 30, 35, and 40°C. The time spent in each instar and survival was recorded. Developmental rate increased with temperature from 15 to 30°C for all instars, then declined again at higher temperatures. Nymphal survival was lower at 35°C than between 15 and 30°C for all instars, and first instars placed at 5, 10, and 40°C all died without molting. This suggests that L. delicatula survival and development may be affected in the Southern United States by high temperatures and developmental delays will occur under cool spring conditions. The lower developmental threshold was found to be 13.00 ± 0.42°C for first instars, 12.43 ± 2.09°C for second instars, 8.48 ± 2.99°C for third instars, and 6.29 ± 2.12°C for fourth instars. The degree-day (DD) requirement for nymphs in the previous instar to complete development to reach the second instar, third instar, fourth instar, and adult was 166.61, 208.75, 410.49, and 620.07 DD (base varied), respectively. These results provide key data to support the development of phenology models and help identify the potential range of L. delicatula in North America.

Thermal requirements and life table parameters of the predatory mite, Neoseiulus californicus (McGregor) fed on Tetranychus urticae Koch (Acari: Phytoseiidae: Tetranychidae)

The predatory mite, Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) is an important biological control agent of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) infesting many crops worldwide. Biology, life table parameters and thermal requirements of N. californicus were evaluated in laboratory at 20, 27, 30±2oC and 70±5% RH. Spider mite, T. urticae is an important pest of soybean crop in Egypt. The duration of the immature stages of N. californicus ranged from 4.22 to 7.35 days for female and from 3.80 to 7.10 days for male when they were kept at 20 and 30°C, respectively. The mean generation time (TG) decreased with increasing temperature from 19.48 days to 12.93 days at 20 to 30°C, respectively. The intrinsic rate of increase (rm) and finite rate of increase (λ) were highest at 27 and 30 oC. The highest total consumption rate of prey was 223.4 individuals when adult female fed on T. urticae motile stages at 30 oC, while the lowest rate was 162.60 individuals at 20 oC during the whole life span. Minimum developmental thresholds (t0) of egg, larva, protonymph, deutonymph and total immature stages of N. californicus female averaged 13.20, 12.75, 3.29, 0.0 and 6.66 oC, respectively. The predatory female of N. californicus required 500 DDUs to reach adulthood. Therefore, a thermal range of 27oC was the most suitable condition to rear the target predatory mite.

Effects of temperature on life histories of three endangered Japanese diving beetle species

AbstractTo elucidate population‐increasing factors in the diving beetle Cybister tripunctatus lateralis (Fabricius) (Coleoptera: Dytiscidae) in Japan in recent years, life histories and oviposition patterns were compared among three endangered diving beetle species, Cybister brevis Aubé (qualified by the Japanese Red Data List as ‘near threatened’), Cybister chinensis Motschulsky (vulnerable), and C. tripunctatus lateralis (vulnerable). Oviposition in C. brevis, C. chinensis, and C. tripunctatus lateralis was observed from late April to mid‐June, from late April to early July, and from late May to mid‐August, respectively, under semi‐outdoor conditions. There were no interspecies differences in total hatchling production during the reproductive season. In rearing experiments at various temperatures (20, 23, 25, 28, and 30 °C), the mortality of C. tripunctatus lateralis larvae was higher at 20 °C, and gradually lower with increasing temperature up to 30 °C. Adult body size of females in C. tripunctatus lateralis is larger than that of males but there were no significant differences among temperatures (25–30 °C). Cybister brevis had a higher emergence rate at 23–28 °C than at 20 and 30 °C. In C. brevis, the body size of adults reared at 25 or 28 °C was significantly larger than at other temperatures. Cybister chinensis did not differ in emergence rate and adult body size among the five temperature conditions. The developmental zero (i.e., the lower developmental threshold) from the first instar to adult emergence was 11.1 °C for C. brevis, 8.7 °C for C. chinensis, and 16.8 °C for C. tripunctatus lateralis. We speculate how the influence of global warming may have a positive impact on the growth and survival of C. tripunctatus lateralis.

Thermal biology of Tuta absoluta: demographic parameters and facultative diapause

The South American tomato pinworm, Tuta absoluta, (SATP) is now a devastating pest worldwide of crops in the family Solanaceae. Most prior studies of SATP’s thermal biology were based on populations from tropical regions, and proved unsuitable for explaining its invasion of large areas of the Palearctic. A more holistic approach to the analysis of its thermal biology is essential background for developing models to assess its invasive potential. Our studies found that SATP has lower and upper thermal thresholds (θL = 5.37 °C and θU = 35.69 °C, respectively) than South American populations used in prior studies (θL = 7.38 °C and θU = 33.82 °C). Age-specific life tables were used to estimate the effects of temperature on its demographic parameters. Diapause in SATP had not been characterized prior to our study. We found facultative diapause in pupae developing from larvae exposed to relatively low temperatures (i.e., 2 and 5 °C) and short-day length for different exposure periods. The strength of diapause was measured as an increase in post-treatment developmental times of pupae (i.e., degree days) that on average were 2.45–3-fold greater than of pupae reared at favorable temperatures. A lower developmental threshold and a facultative diapause increase the invasive potential of SATP in temperate areas. Knowledge of this thermal biology is essential for predicting the potential geographic spread of this pest and to develop management and control strategies.

Deciphering the effect of climate warming on an emerging poplar pest using spatial extrapolation of population parameters

Abstract The woolly poplar aphid Phloeomyzus passerinii Signoret (Aphididae: Phloeomyzinae) is a major pest of poplar plantations. We hypothesized that recent temperature increases may have contributed to the emergence and subsequent northward expansion of outbreaks in France. We reared P. passerinii at four temperatures to estimate its thermal requirements. We used experimental data to parametrize a mechanistic and temperature‐driven physiologically‐based demographic model. The model was used to simulate the effect of temperature on aphid dynamics and to assess the role of climate warming on the spatiotemporal dynamics of outbreaks. The lower developmental threshold was estimated at 6.4 °C and the development degree‐days at 171. Our model supports the hypothesis that recent warming may have promoted outbreaks in northern France. During recent exceptionally warm years, more than 70% of the northern poplar area was favourable for outbreaks. Our model suggests that climate warming is not the sole factor involved. The dominance of resistant poplar genotypes such as ‘Robusta’ or ‘Beaupré’ may have preserved plantations from outbreaks before 1996 in southern France and until 2000 in the central part. Other factors, including biological characteristics, biotic interactions, or precipitation should be investigated.