Incidence Of Diapause Research Articles

Photoperiod‐independent diapause‐inducing thermal response of Trichogramma larvae: Pattern and mechanisms

AbstractIt is well known that photoperiodic induction of insect diapause can be affected by temperature, whereas photoperiod‐independent diapause‐inducing thermal responses received much less attention of researchers. We studied the influence of a wide range (from 3 to 30°C) of constant and alternating temperatures on the rate of development, on pre‐adult survival and on the induction of pre‐pupal diapause in the egg parasitoid Trichogramma telengai. The progeny of females developed at 20°C and photoperiod of L:D = 18:6 or 12:12 was used in this study. The study showed that the pattern of the thermal response of T. telengai is an asymmetric inverted U‐shaped curve determined by two different mechanisms. The right part of the curve represents S‐shaped effect of temperature on the induction of diapause (the threshold for this response is 13–15°C depending on maternal photoperiod), whereas the left part represents an arrest of development caused by the direct effect of low temperature (with the threshold of about 5°C). We conclude that the effect of temperature on the induction of diapause in T. telengai is based on (or at least closely connected with) the thermal influence on the rate of metabolism and development. The results of this study can be used for the prediction of Trichogramma diapause incidence under natural conditions and for the development of the cold storage methods.

A comparative analysis of Aedes albopictus and Aedes aegypti subjected to diapause-inducing conditions reveals conserved and divergent aspects associated with diapause, as well as novel genes associated with its onset.

Aedes albopictus and Aedes aegypti are mosquito species that are distributed worldwide and transmit diverse arboviruses of medical importance, such as those causing yellow fever, dengue, chikungunya and Zika. A. albopictus embryos may remain viable for long periods in the environment due to their ability to become dormant through quiescence or diapause, a feature that contributes to their dispersion and hinders control actions. Diapause incidence can vary among natural populations of A. albopictus, but metabolic and genetic parameters associated with its induction still need to be better defined. The present study aimed to investigate the effect of exposure to diapause-inducing conditions on several biological parameters in different populations of A. albopictus (from tropical and temperate areas) and the diapause-refractory A. aegypti (tropical and subtropical populations). As expected, only the A. albopictus populations exhibited diapause, but with a lower incidence for the population from a tropical area. Exposure to diapause-inducing conditions, however, led to a sharp reduction in fecundity for both A. albopictus and A. aegypti tropical populations, with no effect on fertility (>90%). It also led to a prolonged period as pupae for the progeny of all induced groups, with a further delay for those from temperate climates. In all those induced groups, the lipid contents in eggs and adult females were higher than in the non-induced controls, with the highest values observed for both A. albopictus groups. Three genes were selected to have their expression profile investigated: cathepsin, idgf4, and pepck. Upon exposure to diapause-inducing conditions, all three genes were upregulated in the A. albopictus embryos from the tropical region, but only idgf4 was upregulated in the temperate climate embryos. This represents a new gene associated with diapause that can be used as a target to evaluate and prevent embryonic dormancy, a possible new vector control strategy for mosquito species from temperate areas, such as A. albopictus.

Thermal history of alfalfa leafcutting bees affects nesting and diapause incidence.

Variable spring temperatures may expose developing insects to sublethal conditions, resulting in long-term consequences. The alfalfa leafcutting bee, Megachile rotundata, overwinters as a prepupa inside a brood cell, resuming development in spring. During these immobile stages of development, bees must tolerate unfavorable temperatures. In this study, we tested how exposure to low temperature stress during development affects subsequent reproduction and characteristics of the F1 generation. Developing male and female M. rotundata were exposed to either constant (6°C) or fluctuating (1 hday-1 at 20°C) low temperature stress for 1week, during the pupal stage, to mimic a spring cold snap. Treated adults were marked and released into field cages, and reproductive output was compared with that of untreated control bees. Exposure to low temperatures during the pupal stage had mixed effects on reproduction and offspring characteristics. Females treated with fluctuating low temperatures were more likely to nest compared with control bees or those exposed to constant low temperature stress. Sublethal effects may have contributed to low nesting rates of bees exposed to constant low temperatures. Females from that group that were able to nest had fewer, larger offspring with high viability, suggesting a trade-off. Interestingly, offspring of bees exposed to fluctuating low temperatures were more likely to enter diapause, indicating that thermal history of parents, even during development, is an important factor in diapause determination.

A Comparative Study of Circadian Rhythmicity and Photoperiodism in Closely Related Species of Blow Flies: External Coincidence, Maternal Induction, and Diapause at Northern Latitudes.

This review compares adult locomotor activity rhythms and photoperiodic induction of diapause in 3 common species of blow fly, Calliphora vicina, Lucilia sericata, and Protophormia terraenovae. Activity rhythms were broadly similar in all 3 species, although P. terraenovae is much less sensitive to constant light inducing arrhythmicity. Photoperiodic induction of diapause, on the other hand, varies more widely between species. C. vicina and L. sericata overwinter in a larval diapause induced by autumnal short days (long nights) acting both maternally and directly upon the larvae. P. terraenovae, on the other hand, shows an adult (reproductive) diapause induced by short daylength and low temperature experienced by the larvae. In the Nanda-Hamner protocol, C. vicina shows 3 clear peaks of high diapause incidence in cycle lengths close to 24, 48, and 72 h, without dampening and therefore suggesting a photoperiodic mechanism based on a self-sustained circadian oscillator acting in a clock of the external coincidence type. Entrainment of the locomotor activity rhythm to extended Nanda-Hamner photocycles, as well as to LD cycles close to the limits of the primary range of entrainment, demonstrates that overt circadian rhythmicity may act as ‘hands’ of the otherwise covert photoperiodic system, as suggested by Bünning, nearly 8 decades ago. In 24 h LD cycles, both locomotor activity rhythms and the photoperiodic oscillator are set to constant phase (CT 12) at light-off, so that the photoperiodic clock measures changes in nightlength by the coincidence (or not) of dawn light with a ‘photoinducible phase’ late in the subjective night (at about CT 21.5 h) as photoperiod changes with the seasons. Apparent differences between quantitative and qualitative photoperiodic responses are discussed.

Temperature and Photoperiodic Response of Diapause Induction in Anastatus japonicus, an Egg Parasitoid of Stink Bugs.

Simple SummaryAnastatus japonicus Ashmead is an important egg parasitoid wasp and natural enemy of Tessaratoma papillosa. It is commercially used in biological control, and has effectively suppressed T. papillosa population for decades in China. In practice, medium temperature in spring always induces diapause in A. japonicus, leading to the delay of adult emergence and missing the best chance to control the pest. Accurately regulating the development of A. japonicus is a key technique for the production of biocontrol agents and field release applications. In this study, responsible environmental factors for the induction of diapause in A. japonicus were investigated. A short photoperiod and medium temperature led to diapause in A. japonicus. Second–third instar larva are the most sensitive stages to diapause stimuli. Diapausing mature larvae had a significantly higher survival rate after 180 days storage at 10 °C than that of nondiapausing mature larvae. Taken together, results suggest methods that could be exploited in the developmental regulation, field-release pretreatment technology, and long-term storage of A. japonicus.Anastatus japonicus Ashmead is a widely used biological control agent against stink bugs that can be successfully reared using the large eggs of the Chinese silkworm. In this study, environmental factors responsible for the induction of diapause in A. japonicus were investigated on host eggs of the Chinese silkworm. A. japonicus exhibited a facultative, mature larval diapause within its host eggs. Second–third instar larva are the most sensitive stages to diapause stimuli. The accumulation of diapause stimuli during all the larval stages maximized the diapause response. A short photoperiod of 10L:14D and temperature of 17 °C led to the occurrence of the highest diapause response, while a long photoperiod (14L:10D) and low temperatures (11 and 14 °C) prevented the diapause. A specific exposure period was required to reach high diapause incidence. Diapausing mature larvae had a significantly higher survival rate after 180 days storage at 10 °C than that of nondiapausing mature larvae. Taken together, results suggest methods that could be exploited in the developmental regulation, field-release pretreatment technology, and long-term storage of A. japonicus.

Environmental impacts on diapause and survival of the alfalfa leafcutting bee, Megachile rotundata

Megachile rotundata exhibits a facultative prepupal diapause but the cues regulating diapause initiation are not well understood. Possible cues include daylength and temperature. Megachile rotundata females experience changing daylengths over the nesting season that may influence diapause incidence in their offspring through a maternal effect. Juvenile M. rotundata spend their developmental period confined in a nesting cavity, potentially subjected to stressful temperatures that may affect diapause incidence and survival. To estimate the impact of daylength and nest cavity temperature on offspring diapause, we designed a 3D printed box with iButtons that measured nest cavity temperature. We observed nest building throughout the season, monitored nest cavity temperature, and followed offspring through development to measure diapause incidence and mortality. We found that daylength was a cue for diapause, and nest cavity temperature did not influence diapause incidence. Eggs laid during long days had a lower probability of diapause. Siblings tended to have the same diapause status, explaining a lot of the remaining variance in diapause incidence. Some females established nests that contained both diapausing and nondiapausing individuals, which were distributed throughout the nest. Nest cavities reached stressful temperatures, which decreased survival. Mortality was significantly higher in nondiapausing bees and the individuals that were laid first in the nest. In conclusion, we demonstrate a maternal effect for diapause that is mediated by daylength and is independent of nest box temperature.

Urban warming and artificial light alter dormancy in the flesh fly.

Seasonal changes in temperature and day length are distinct between rural and urban areas due to urban warming and the presence of artificial light at night. Many studies have focused on the impacts of these ubiquitous signatures on daily biological events, but empirical studies on their impacts on insect seasonality are limited. In the present study, we used the flesh fly Sarcophaga similis as a model insect to determine the impacts of urbanization on the incidence and timing of diapause (dormancy), not only in the laboratory but also in rural and urban conditions. In the laboratory, diapause entry was affected by night-time light levels as low as 0.01 lux. We placed fly cages on outdoor shelves in urban and rural areas to determine the timing of diapause entry; it was retarded by approximately four weeks in urban areas relative to that in rural areas. Moreover, almost all flies in the site facing an urban residential area failed to enter diapause, even by late autumn. Although an autumnal low temperature in the urban area would mitigate the negative effect of artificial light at night, strong light pollution seriously disrupts the flesh fly seasonal adaptation.

Geographic Variation in Photoperiodic Response for Induction of Pseudopupal Diapause in Epicauta gorhami (Coleoptera: Meloidae).

Geographical variations in the threshold of environmental cues for diapause induction are important in understanding the life history strategy of insects. Larvae of the bean blister beetle, Epicauta gorhami (Coleoptera: Meloidae), feed on grasshopper eggs and undergo hypermetamorphosis. They normally enter diapause as a pseudopupa (fifth instar). However, when the larvae are reared under long-day and high-temperature conditions, they do not enter pseudopupal diapause but pupate directly from the fourth instar. In addition, this insect is known to modify its photoperiodic response for induction of pseudopupal diapause depending on food availability for larvae. In this study, the larval photoperiodic responses for diapause induction were examined for three populations of E. gorhami collected from the northernmost (Morioka, 39.7°N), central (Kazo, 36.1°N), and southernmost (Takanabe, 32.1°N) parts of its distribution range, and the responses were examined under both fully fed and food-deprived (FD) conditions. Diapause incidence decreased in FD larvae for all populations in long-day conditions, and the critical day-lengths for the diapause incidence were calculated as 14.81, 13.97, and 13.99 h in the Morioka, Kazo, and Takanabe populations, respectively. The results indicate the presence of a geographical variation in larval photoperiodic response, in which diapause is induced earlier in higher latitudinal areas. From these results, together with data for developmental threshold temperature and thermal constant, the Morioka and Kazo populations were suggested to have a partial bivoltine life cycle under the conditions of extremely early oviposition season, a sufficient summer temperature, and poor larval food availability.

Influence of temperature on the restoration of the ability of Trichogramma principium to undergo diapause

It is known that the progeny of post-diapause females of some insects are insensitive to diapause-inducing stimuli. In aphids the duration of the ‘interval timer’ (the restoration of the ability to diapause) decreases with temperature. However, the parameters of this temperature dependence are unknown. We investigated the restoration of the ability to undergo diapause in 9–16 sequential post-diapause generations of the egg parasitoid Trichogramma principium Sug. et Sor. (Hymenoptera: Trichogrammatidae) over a period of 120–150 days at different constant and variable temperatures. This revealed a strong linear correlation between mean temperature and the rate of the restoration of the ability to diapause. The lower temperature threshold of this dependence was not significantly different from that of the thermal dependence of the rate of preimaginal development. The restoration rate depended on the mean temperature for the whole period of development rather than on the temperature conditions during the development of the thermosensitive stages determining the incidence of diapause in the progeny. The results of this study indicate that the duration of the interval timer is determined by the rate of development (or, more generally, by the rate of metabolism) rather than by the mechanisms controlling the photothermal regulation of diapause.

Critical Photoperiod and Its Potential to Predict Mosquito Distributions and Control Medically Important Pests.

Diapause, a period of arrested development that allows mosquitoes to survive inhospitable conditions, is triggered by short daylengths in temperate mosquitoes. Different populations of mosquitoes initiate diapause in response to a specific photoperiod, or daylength, resulting in population-specific differences in annual cycles of abundance. The photoperiod that causes approximately 50% of a population to initiate diapause is known as the critical photoperiod (CPP). The autumn daylength corresponding to the CPP in the field likely marks the day beyond which the photoperiods would trigger and maintain 50% or more diapause incidence in a population, although temperature, diet, and other factors can impact diapause initiation. In the Northern Hemisphere, northern populations of mosquitoes experience lower temperatures earlier in the year and must be triggered into diapause by longer daylengths than southern populations. CPP is genetically based, but also adapts over time responding to the population's environment. Therefore, CPP has been shown to lengthen with increasing latitude and altitude. While the positive correlation between CPP and latitude/altitude has been established in a few mosquito species, including Aedes albopictus (Skuse, Diptera: Culicidae), Aedes triseriatus, Aedes sierrensis, and Wyeomyia smithii (Coquillett, Diptera: Culicidae), we do not know when most other species initiate their seasonal responses. As several of these species transmit important diseases, characterizing the CPP of arthropod vectors could improve existing control by ensuring that surveillance efforts align with the vector's seasonally active period. Additionally, better understanding when mosquitoes and other vectors initiate diapause can reduce the frequency of chemical applications, thereby ameliorating the negative impacts to nontarget insects.

Plasticity of nutrient accumulation patterns in diapausing fall webworm pupae.

The accumulation of nutrients during diapause preparation is crucial because any lack of nutrition will reduce the likelihood of insects completing diapause, thereby decreasing their chances of survival and reproduction. The fall webworm, Hyphantria cunea, diapause as overwintering pupae and their diapause incidence and diapause intensity are regulated by the photoperiod. In this study, we test the hypothesis that photoperiod influences energy reserve accumulation during diapause preparation in fall webworm. We found that the body size and mass, lipid and carbohydrate content of pupae with a short photoperiod during the diapause induction phase were significantly greater than those of pupae with a relatively short photoperiod, and the efficiency of converting digested food and ingested food into body matter was greater in the short-photoperiod diapause-destined larvae than the relatively short-photoperiod diapause-destined larvae. We also observed higher lipase and amylase activities in short-photoperiod diapause-destined larvae relative to the counterparts. However, no obvious difference was found in protein and protease in the pupae with a short photoperiod during the diapause induction phase and short-photoperiod diapause-destined larvae compared with the counterparts. Therefore, we conclude that the energy reserve patterns of diapausing fall webworm pupae are plastic and that short-photoperiod diapause-destined larvae increase their energy reserves by improving their feeding efficiency and increase their lipid and carbohydrate stores by increasing the lipase and amylase activities in the midgut.

Voltine Ecotypes of the Asian Corn Borer and Their Response to Climate Warming.

Simple SummaryThe Asian corn borer (ACB), Ostrinia furnacalis, is an important economic pest of corn and other crops, and is widely distributed in China. Depending on the climate, ACB may have one or up to seven generations each year, from north to south, respectively. The degree of crop damage is closely related to its phenology and number of generations per year (voltinism). Climate warming may result in an alternation of voltinism in the ACB. In the present study, we investigated the voltinism of different populations under different simulated environments. From the diapause response, both the uni- and multivoltine ecotypes were coexisting in the Harbin (H) population collected from action sites of ACB moths in Harbin, Heilongjiang Province, China. Diapause incidence declined given the climate-warming scenario, which was temporally specific and could be overridden by significantly low daily average temperatures. Elevated CO2 did not directly impact voltinism. On the basis of voltinism, the H population reflected sympatric uni- and multivoltine ecotypes, with multivoltinism being dominant. The univoltinism trait was recessive. Climate warming could significantly override photoperiod effects. Warmer temperatures and declining latitude (reduced daylength), and their interaction, are estimated to drive ACB evolution to increased homogeneity and multivoltinism.In the Asian corn borer (ACB), Ostrinia furnacalis (Guenée), diapause is governed by a multigenetic constitution that responds to daylength and temperature with seasonality. The ACB displays uni- or multivoltinism, depending on its geographic specificity. Hence, warmer temperatures may result in alternation of voltinism in the ACB, which will help in understanding the ecological consequences of climate warming on insects. In the present study, we investigated the voltinism in two natural populations from Harbin (H) and Gongzhuling (G) as well as a laboratory (L) population (established from the H population in 2017) of the ACB, at ambient and elevated atmospheric CO2 (aCO2 390 μL/L and eCO2 750 μL/L) and temperature (aT and Et = At + 2 °C). From the diapause response, both the uni- and multivoltine ecotypes were coexisting in the H population. The neonate occurrence date of 50% individuals that induced diapause was ca. 10 days later in the G population than in the H population, but it was about 10 days earlier than in the L population. Comparing to the dates of onset and the peak of diapause induction, the G and L populations were less variable than the H population in response to a short and/or shortening daylength in the field. The univoltine individuals could not be eliminated completely after 19 generations of selection. Diapause incidence decreased with a climate-warming scenario, which was temporally specific and could be overridden by significantly low daily average temperatures. The eCO2 did not directly impact the voltinism. On the basis of voltinism, the H population was sympatric for uni- and multivoltine ecotypes, with multivoltinism being dominant. The univoltinism trait was recessive. Climate warming could significantly override the effect of photoperiod, which was yearly dependent. Warmer temperatures and a decreased latitude (shortened daylength), and their interaction, would drive ACB evolution toward diapause homogeneity for multivoltinism.

Effects of three host pine species on diapause induction and life-history traits of Monochamus alternatus alternatus (Coleoptera: Cerambycidae)

ABSTRACT Monochamus alternatus alternatus Hope is distributed in China and Taiwan and transmits the pinewood nematode, the causative agent of pine wilt disease. Unlike univoltine and semivoltine Monochamus alternatus endai Makihara native to Japan, M. a. alternatus has two generations a year (bivoltinism). Some polyphagous insect herbivores exhibit that the incidence of diapause is affected by the host plant species on which they feed, resulting in a host plant dependent variation in the number of generations a year (voltinism). For evaluating the effects of alien pine species on the colonization of M. a. alternatus, its larvae were reared on bolts of Pinus densiflora and P. thunbergii native to Japan and P. echinata native to North America in the laboratory. This study indicated that the three pine species did not increase the incidence of larval diapause to 1.0, suggesting that any pine species did not change the voltinsim. It also determined that the pine species did not influence the ovariole number of females that forwent diapause. The impact of feeding on P. densiflora and P. thunbergii on adult body mass was variable and there was no difference in adult body mass between P. densiflora and P. echinata. Thus, this study suggested that the voltinism of M. a. alternatus was not altered by some pine species native to unoccupied regions such as Japan and North America, i.e. its reproductive rate per year did not decrease owing to reduced number of generations per year, when it arrived there and then colonized.

Modelling the combined effects of photoperiod and temperature on diapause induction in Apolygus lucorum (Meyer-Dür) across different latitudes.

The green mirid bug Apolygus lucorum is a dominant pest species on multiple crops over a wide area in northern China. However, the combined effect of photoperiod and temperature on diapause induction in this species across different latitudes is not clear. Thus, the combined effects of temperature (17-29 °C) and photoperiod (11:13 h to 15:9 h light/dark) on diapause induction for seven geographic populations, collected at latitudes between 30.47°N and 38.30°N, were investigated. A model, I = (15 - p)/(30 - p - 1.923(t - 16)1/2 + 0.4499 t - 0.015 L - 19.5389) was established to predict diapause incidence (I) using photophase (p), temperature (t) and latitude (L). In most cases, the diapause incidence predicted by the model was within or close to the 95% confidence interval estimated from independently observed field data. Diapause incidence in A. lucorum was influenced nonlinearly by temperature and photoperiod across different latitudes. The model established in this study is valid for predicting diapause incidence in this pest over a wide area in northern China, and thus can be incorporated into an areawide population dynamic model of this pest. © 2020 Society of Chemical Industry.

Inverse density-dependent diapause and its influence on population dynamics in Monochamus alternatus alternatus (Coleoptera: Cerambycidae)

Monochamus alternatus alternatus Hope (Coleoptera: Cerambycidae) is the primary vector of pine wilt disease in China and Taiwan. It has a partially bivoltine life cycle with facultative diapause at the final larval instar that is mediated by the initial larval density. To evaluate the effect of density-related induction of diapause on population fluctuation, one, two or four newly hatched larvae were inoculated on individual Pinus thunbergii bolts and the life-history traits including diapause were investigated. This experiment indicated that as initial population size/bolt (crowding) increased, the diapause incidence, larval stage survival, adult body size, development time of nondiapause individuals and pupal period of diapause individuals decreased. The analysis indicated that larval interference as well as food shortage suppressed diapause induction. Increasing larval density decreased the probability of diapausing, survival, adult body mass and other traits. Using the data obtained from this study, a simple mathematical model indicated that inverse density-dependent induction of diapause in the first generation had a destabilizing effect on the population size of overwintering generation, which was composed of diapause larvae of the first and second generations; whereas, direct density-dependent induction of diapause exerted a stabilizing effect on it.

Diapause characterisation and seasonality of Aedes japonicus japonicus (Diptera, Culicidae) in the northeast of France.

The invasive mosquito Aedes japonicus japonicus (Theobald, 1901) settled in 2013 in the Alsace region, in the northeast of France. In this temperate area, some mosquito species use diapause to survive cold winter temperatures and thereby foster settlement and dispersal. This study reports diapause and its seasonality in a field population of Ae. japonicus in the northeast of France. For two years, eggs were collected from May to the beginning of November. They were most abundant in summer and became sparse in late October. Diapause eggs were determined by the presence of a fully developed embryo in unhatched eggs after repeated immersions. Our study showed effective diapause of Ae. japonicus in this part of France. At the start of the egg-laying period (week 20), we found up to 10% of eggs under diapause, and this rate reached 100% in October. The 50% cut-off of diapause incidence was determined by the end of summer, leading to an average calculated maternal critical photoperiod of 13 h 23 min. Interestingly, diapause was shown to occur in part of the eggs even at the earliest period of the two seasons, i.e. in May of each year. Even though we observed that the size of eggs was positively correlated with diapause incidence, morphology cannot be used as the unique predictive indicator of diapause status due to overlapping measurements between diapausing and non-diapausing eggs. This study provides new knowledge on diapause characterisation and invasive traits of Ae. japonicus.

Transgenerational Plasticity and Bet-Hedging: A Framework for Reaction Norm Evolution

Decision-making under uncertain conditions favors bet-hedging (avoidance of fitness variance), whereas predictable environments favor phenotypic plasticity. However, entirely predictable or entirely unpredictable conditions are rarely found in nature. Intermediate strategies are required when the time lag between information sensing and phenotype induction is large (e.g., transgenerational plasticity) and when cues are only partially predictive of future conditions. Nevertheless, current theory regards plasticity and bet-hedging as distinct entities. We here develop a unifying framework: based on traits with binary outcomes like seed germination or diapause incidence we clarify that diversified bet-hedging (risk-spreading among one’s offspring) and transgenerational plasticity are mutually exclusive strategies, arising from opposing changes in reaction norms (allocating phenotypic variance among or within environments). We further explain the relationship of this continuum with arithmetic mean maximization vs. conservative bet-hedging (a risk-avoidance strategy), and canalization vs. phenotypic variance in a three-dimensional continuum of reaction norm evolution. We discuss under which scenarios costs and limits may constrain the evolution of reaction norm shapes.

Diapause induction in Eotetranychus smithi (Acari: Tetranychidae): effect of average temperature, but not of thermoperiod

AbstractFacultative diapause of Eotetranychus smithi appears to occur at the egg stage and is induced by temperatures ≤17.5 °C, independent of photoperiod. However, the effect of thermoperiod on the induction of diapause remains unclear. To answer this question, we exposed female E. smithi to various thermoperiods under constant light conditions. First, we found that the deposition order of eggs affected the incidence of diapause: the first eggs (exclusively males) tended to avert diapause compared with the second and third eggs (most of them are females), possibly because of the sex of the eggs. Next, the incidence of diapause of the second eggs decreased with shortening of the cryophase, which was associated with an increase of the average temperature, and it showed clear long‐day‐type thermoperiodic response curves. However, this species does not sense the ratio of day (thermophase) to night (cryophase) of a given thermoperiod. Short thermoperiods did not increase the incidence of diapause, but rather precluded the entry into diapause. We detected no sign of the involvement of the circadian system in diapause induction in the thermoperiodic Nanda–Hamner protocol. We conclude that diapause induction of E. smithi does not involve the circadian system, and thus does not show thermoperiodism. Diapause induction under the various thermoperiodic conditions tested in the present study appears to be derived from the temperature itself. E. smithi is an exceptional species that relies on temperature alone to induce diapause.

Temperature and photoperiod effects on dormancy status and life cycle parameters in Aedes albopictus and Aedes aegypti from subtropical Argentina.

Aedes albopictus (Diptera: Culicidae) distribution is bounded to a subtropical area in Argentina, while Aedes aegypti (Diptera: Culicidae) covers both temperate and subtropical regions. We assessed thermal and photoperiod conditions on dormancy status, development time and mortality for these species from subtropical Argentina. Short days (8 light:16 dark) significantly increased larval development time for both species, an effect previously linked to diapause incidence. Aedes albopictus showed higher mortality than Ae. aegypti at 16 °C under long day treatments (16 light:8 dark), which could indicate a lower tolerance to a sudden temperature decrease during the summer season. Aedes albopictus showed a slightly higher percentage of dormant eggs from females exposed to a short day, relative to previous research in Brazilian populations. Since we employed more hours of darkness, this could suggest a relationship between day-length and dormancy intensity. Interestingly, local Ae. aegypti presented dormancy similar to Ae. albopictus, in accordance with temperate populations. The minimum dormancy in Ae. albopictus would not be sufficient to extend its bounded distribution. We believe that these findings represent a novel contribution to current knowledge about the ecophysiology of Ae. albopictus and Ae. aegypti, two species with great epidemiological relevance in this subtropical region.

Cold Nights, City Lights: Artificial Light at Night Reduces Photoperiodically Induced Diapause in Urban and Rural Populations of Aedes albopictus (Diptera: Culicidae).

As the planet becomes increasingly urbanized, it is imperative that we understand the ecological and evolutionary consequences of urbanization on species. One common attribute of urbanization that differs from rural areas is the prevalence of artificial light at night (ALAN). For many species, light is one of the most important and reliable environmental cues, largely governing the timing of daily and seasonal activity patterns. Recently, it has been shown that ALAN can alter behavioral, phenological, and physiological traits in diverse taxa. For temperate insects, diapause is an essential trait for winter survival and commences in response to declining daylight hours in the fall. Diapause is under strong selection pressure in the mosquito, Aedes albopictus (Skuse); local adaptation and rapid evolution has been observed along a latitudinal cline. It is unknown how ALAN affects this photosensitive trait or if local adaptation has occurred along an urbanization gradient. Using a common garden experiment, we experimentally demonstrated that simulated ALAN reduces diapause incidence in this species by as much as 40%. There was no difference, however, between urban and rural demes. We also calculated diapause incidence from wild demes in urban areas to determine whether wild populations exhibited lower than predicted incidence compared to estimates from total nocturnal darkness. In early fall, lower than predicted diapause incidence was recorded, but all demes reached nearly 100% diapause before terminating egg laying. It is possible that nocturnal resting behavior in vegetation limits the amount of ALAN exposure this species experiences potentially limiting local adaptation.