Diapause Survival Research Articles

Hormetic response to pesticides in diapausing bees.

Pollinators face declines and diversity loss associated with multiple stressors, particularly pesticides. Most pollination services are provided by annual bees that undergo winter diapause, and many common pesticides are highly soluble in water and move through soil and plants where bees hibernate and feed, yet the effects of pesticides on pollinators' diapause survival and performance are poorly understood. Pesticides may have complex effects in bees, and some were shown to induce hormetic effects on various traits characterized by high-dose inhibition coupled with low-dose stimulation. Here, we examined the occurrence of hormesis in the responses of bees to imidacloprid. We found that while longevity and reproduction were reduced following exposure to imidacloprid, the survival length of new queens (gynes) was greater. Diapause is a critical period in the life cycle of most bees with profound effects on their health. Exposure to sublethal doses of pesticides may increase bees' resistance to stress/cold during diapause but may also trade off with reduced reproductive performance later in life. Identifying these trade-offs is crucial to understanding how stressors affect pollinator health and should be accounted for when assessing pesticide risk, designing studies and facilitating conservation and management tools for supporting annual bees during diapause.

Symptomatic Infection with Vairimorpha spp. Decreases Diapause Survival in a Wild Bumble Bee Species (Bombus griseocollis).

Vairimorpha, a microsporidian parasite (previously classified as Nosema), has been implicated in the decline of wild bumble bee species in North America. Previous studies examining its influence on colony performance have displayed variable results, from extremely detrimental effects to no observable influence, and little is known about the effects it has on individuals during the winter diapause, a bottleneck for survival in many annual pollinators. Here, we examined the effect of Vairimorpha infection, body size, and mass on diapause survival in Bombus griseocollis gynes. We demonstrate that gyne survival length in diapause is negatively affected by symptomatic Vairimorpha infection of the maternal colony but does not correlate with individual pathogen load. Our findings further indicate that increased body mass offers a protective effect against mortality during diapause in infected, but not in healthy, gynes. This suggests that access to adequate nutritional resources prior to diapause might offset the harmful effect of Vairimorpha infection.

First field-based estimates of bumblebee diapause survival rates showcase high survivorship in the wild.

Bumblebee (Bombus spp.) queens overwintered in artificial settings tend to have low survival rates, raising concerns that diapause may be a particularly sensitive life cycle stage for this ecologically and economically valuable group of pollinators. However, it remains unclear whether lab-based estimates of diapause survival are comparable to survival rates of natural populations. In this study, we monitored the survival of Bombus impatiens queens overwintering in the field in Ipswich, MA, and conducted a meta-analysis of studies that estimate queen diapause survival in the lab to compare our field-based estimates of survival to those of lab-based studies. We found that queen B. impatiens had relatively high rates of overwintering survival after about six months (> 60%), especially when compared to estimates of six-month survival from lab studies (< 10%). We also observed a trend that broadly corroborates many lab studies of bumblebees, in that overwinter survival of queens was related to colony origin. In addition to providing the first estimate of diapause survival for bumblebee queens in nature, our study emphasizes the need to verify patterns observed in the lab to field-based studies. Although protecting target species during sensitive life cycle stages is a fundamental goal of conservation ecology, it is first necessary to identify at what stages of the life cycle populations are most vulnerable. Our results suggest that, at least in some study systems, diapause survival of queen bumblebees in the field may be higher than suggested by lab studies. The online version contains supplementary material available at 10.1007/s10841-023-00478-8.

The Effect of Pollen Diet Composition and Quantity on Diapause Survival and Performance in an Annual Pollinator (Bombus Impatiens).

Most pollination services are provided by annual bees that go through a winter diapause, during which they are exposed to extreme temperatures, pathogens, and starvation. The ability of bees to successfully face these stressors during diapause and subsequently initiate a nest depends on their overall nutritional state and an adequate preparatory diet. Here, we used queens of the common eastern bumble bee, Bombus impatiens, to examine how pollen diets varying in their protein to lipid ratio and total nutrient amounts affected queen performance during and after diapause. We compared diapause survival and reproductive performance post-diapause across different diets and found that queen survival was highest when pollen had a nutritional ratio of approximately 5:1 (protein to lipid). This diet is significantly enriched in proteins compared to the pollen fed to bumble bees in the lab (1:1) or commonly available in agricultural landscapes. Altering the quantity of macronutrients within this ratio did not improve survival or performance. Our results emphasize the importance of adequate nutrition for diapause performance in bees with annual life cycles and the importance of providing annual bees with floral provisioning based on their individual nutritional targets.

Shifting precipitation regimes alter the phenology and population dynamics of low latitude ectotherms

Predicting how species respond to changes in climate is critical to conserving biodiversity. Modeling efforts to date have largely centered on predicting the effects of warming temperatures on temperate species phenology. In and near the tropics, the effects of a warming planet on species phenology are more likely to be driven by changes in the seasonal precipitation cycle rather than temperature. To demonstrate the importance of considering precipitation-driven phenology in ecological studies, we present a case study wherein we construct a mechanistic population model for a rare subtropical butterfly (Miami blue butterfly, Cyclargus thomasi bethunebakeri) and use a suite of global climate models to project butterfly populations into the future. Across all iterations of the model, the trajectory of Miami blue populations is uncertain. We identify both biological uncertainty (unknown diapause survival rate) and climate uncertainty (ambiguity in the sign of precipitation change across climate models), and their interaction as key factors that determine persistence vs. extinction. Despite uncertainty, the most optimistic iteration of the model predicts that Miami blue butterfly populations will decline under the higher emissions scenario (RCP 8.5). The lack of climate model agreement across the projection ensemble suggests that investigations into the effect of climate change on precipitation-driven phenology require a higher level of rigor in the uncertainty analysis compared to analogous studies of temperature. For tropical species, a mechanistic approach that incorporates both biological and climate uncertainty is the best path forward to understand the effect shifting precipitation regimes have on phenology and population dynamics.

Juvenile hormone functions as a metabolic rate accelerator in bumble bees (Bombus terrestris)

Juvenile hormone (JH) is a modulator of many physiological transitions in insects, including molting, metamorphosis, diapause, and reproduction. These processes often include metabolic changes. Here we show that JH accelerates metabolic rate in bumble bees (Bombus terrestris). We reduced JH levels in worker bumble bees by removing their corpora allata (allatectomy) and elevated JH levels in queens through a topical application of JH-III. Natural and high JH levels increased the metabolic rate in both workers and queens and triggered an increased protein turnover rate. Following the treatments, JH also caused an increase in food consumption and a reduction in lipid levels and flight muscle mass of queens, and a reduction in lipids levels in workers. Furthermore, the topical application of a JH analog to queens prior to their diapause caused a decline in their survival of diapause. These findings support the hypothesis that JH acts as a metabolic rate accelerator, initiating a resource shift in bumble bees, and thereby reducing diapause survival in queens. Based on previous studies on JH we suggest that, additional to its behavioral or physiological effects, JH's function as an accelerator of metabolic processes is conserved across different life stages and insect species.

Males from multiple colonies improve queen mating success in the bumblebee Bombus lantschouensis (Hymenoptera: Apidae)

Mating is an important process in bumblebees that could affect queen diapause survival and offspring reproduction. Both queens and males could influence mating failure. Here, we used the indigenous bumblebee Bombus lantschouensis to evaluate the mating interactions of males and gynes. The effects of kin recognition and males and gynes from multiple colonies on mating latency, mating duration, and the mating success rate were investigated. The results showed that gynes mated with related males had a longer mating latency than those mated with unrelated males (42.88 ± 3.8 min and 24.15 ± 2.5 min, respectively, P < 0.05) and that the mating success rate was significantly higher in unrelated groups than in related groups (49.29 ± 4.1% and 36.74 ± 2.6%, respectively, P < 0.05). However, no preference for related or unrelated males was observed in the mixed mating groups (mating success rate 30.63 ± 3.1% and 30.73 ± 2.4%, respectively, P > 0.05). Interestingly, the occurrence of males from multiple sources significantly increased the mating success rate (one colony 39.1 ± 4.2% to four colonies 60.05 ± 5.7%, P < 0.05). Nonetheless, an increase in the number of gyne sources had no effect on the mating success rate (one colony 39.50 ± 4.9% to four colonies 43.52 ± 5.7%, P > 0.05). Mating latency was significantly more influenced by males and gynes from multiple colonies than by kin relationship, male number, and gyne number (P < 0.05). In conclusion, there is no evidence that the bumblebee B. lantschouensis can recognize kin relationships before mating. The presence of males and gynes from multiple colonies can influence mating latency. Moreover, males from multiple colonies can significantly enhance mating success, which has implications for bumblebee ecological conservation and artificial mass rearing.

Optimal Conditions for Diapause Survival of Aprostocetus fukutai, an Egg Parasitoid for Biological Control of Anoplophora chinensis.

Simple SummaryDiapause is a critical state of an insect’s life cycle when it undergoes arrestment of growth and/or reproduction to survive adverse environmental conditions and/or food shortage. Aprostocetus fukutai is a specialist egg parasitoid of the citrus longhorned beetle, Anoplophora chinensis, a high-risk invasive woodboring pest. The parasitoid overwinters as diapausing mature larva in the host egg and emerges in early summer in synchrony with the egg-laying of A. chinensis. Here, we determined the optimal conditions for diapause survival of this parasitoid. We showed that the parasitoid had a low (36.7%) diapause survival rate inside host eggs laid on potted plants due to desiccation or tree wound defense response under semi-natural conditions. Under laboratory rearing conditions, when parasitized host eggs were extracted from wood, the parasitoid did not survive at low humidity (44% RH). Survival rate increased with humidity, reaching the highest at 100% RH. Survival rate also increased with increasing chilling period temperature from 2 to 12.5 °C. Post-diapause developmental time decreased with increased humidity or temperature, but the reproductive fitness of the parasitoid was not significantly affected by the temperature regimes. Overall, high humidity (100% RH) and mild temperatures (12.5 °C) are the most suitable survival conditions for the diapausing parasitoid and thus should be used in laboratory rearing.Aprostocetus fukutai is a specialist egg parasitoid of the citrus longhorned beetle Anoplophora chinensis, a high-risk invasive pest of hardwood trees. The parasitoid overwinters as diapausing mature larvae within the host egg and emerges in early summer in synchrony with the egg-laying peak of A. chinensis. This study investigated the parasitoid’s diapause survival in parasitized host eggs that either remained in potted trees under semi-natural conditions in southern France or were removed from the wood and held at four different humidities (44, 75, 85–93 and 100% RH) at 11 °C or four different temperature regimes (2, 5, 10 and 12.5 °C) at 100% RH in the laboratory. The temperature regimes reflect overwintering temperatures across the parasitoid’s geographical distribution in its native range. Results show that the parasitoid resumed its development to the adult stage at normal rearing conditions (22 °C, 100% RH, 14L:10D) after 6- or 7-months cold chilling at both the semi-natural and laboratory conditions. It had a low survival rate (36.7%) on potted plants due to desiccation or tree wound defense response. No parasitoids survived at 44% RH, but survival rate increased with humidity, reaching the highest (93.7%) at 100% RH. Survival rate also increased from 21.0% at 2 °C to 82.8% at 12.5 °C. Post-diapause developmental time decreased with increased humidity or temperature. There was no difference in the lifetime fecundity of emerged females from 2 and 12.5 °C. These results suggest that 100% RH and 12.5 °C are the most suitable diapause conditions for laboratory rearing of this parasitoid.

Influence of inbreeding in the early stages of artificially reared colonies of Bombus terrestris

AbstractIn the present study on the bumblebee Bombus terrestris, we investigated the influence of inbreeding on queen fitness by comparing diapause survival and egg‐laying success of queens mated with nestmate and non‐nestmate males. We then compared the early stage of colonies with or without diploid males and analysed colony characteristics to identify a factor predictive of colony outcome. Diapause survival was no different between queens mated with nestmates and non‐nestmates, but in the latter case, egg‐laying success was significantly higher. Queens mated with nestmates gave rise to a percentage of diploid male colonies (52.6%) compatible with brother–sister coupling. We obtained 18.6% of colonies with diploid males even from queens mated with non‐nestmates, indicating that the colonies of origin were in some way related or homozygous at the sex determination loci. There was no difference in the early growth stage between colonies with or without diploid males, except in the number of workers emerging in the first brood, which was significantly higher in the latter. Among diploid male colonies, the number of workers and the male/worker ratio in the first brood was highly variable and was not a good predictor of subsequent colony growth. Out of 49 colonies with diploid males that reached full development, only 11 had a sufficient size to assume that they could survive in the field or, in a commercial breeding, to be suitable for pollination purposes.

The effect of intrinsic physiological traits on diapause survival and their underlying mechanisms in an annual bee species Bombus impatiens.

In the face of insect declines, identifying phases of the life cycle when insects are particularly vulnerable to mortality is critical to conservation efforts. For numerous annual insect groups, diapause is both a key adaptation that allows survival of inhospitable conditions and a physiologically demanding life stage that can result in high rates of mortality. As bees continue to garner attention as a group experiencing high rates of decline, improving our understanding of how annual bees prepare for diapause and identifying factors that reduce survival is imperative. Here, we studied factors affecting diapause survival length and their underlying mechanisms using an economically and ecologically important annual bee species, Bombus impatiens. We examined how age and mass upon diapause onset correlate with diapause survival length, and the mechanistic role of nutrient acquisition and oxidative stress post pupal eclosion in mediating these effects. Our findings show that both age and mass were strong predictors of diapause survival length. Heavier queens or queens in the age range of ~6-17days survived longer in diapause. Mass gain was attributed to increases in lipid, protein and glycerol amounts following pupal eclosion, and the ability to deal with oxidative stress was significantly compromised in older pre-diapause queens. Our results demonstrate that age-related shifts in bee physiology and timing of nutrient acquisition may both be critical factors driving diapause survival.

Strong reduction in diapause survival under warm and humid overwintering conditions in a temperate‐zone butterfly

AbstractAnthropogenic climate change poses substantial challenges to biodiversity conservation. Effects of climate change on summer conditions and associated heat and desiccation stress have attracted much research interest, while the implications of changing winter conditions on hibernation have hitherto received fairly little attention. This is surprising as the latter may also strongly affect biodiversity. By investigating the effects of overwintering conditions on diapause and postdiapause survival in a temperate‐zone butterfly, we found that warmer and moister winter conditions substantially decreased survival rates. However, detrimental effects were restricted to survival during diapause and subsequent development and had no clear effects on butterfly performance. We suggest that overwintering survival is an important driver of vulnerability to climate change. Our study stresses the importance of collating more data on overwintering survival in species with different hibernation strategies to predict the impact of ongoing climate change on biodiversity.

Bumble bee queen production in semi-field studies: assessment of endpoints and challenges

Bumble bees (Bombus terrestris L; Hymenoptera, Apidae) provide important pollination services and are commercially used, e.g. in greenhouse cultures. Consequently, the impacts of pesticides on bumble bees were already tested in the past. In the light of the newest EFSA guidance document on the risk assessment of plant protection products for pollinators standardized higher tier studies for pollinators are needed (EFSA 2013). For that reason a ringtest protocol for a bumble bee semi-field study design was developed in the ICPPR Non-Apis working group starting in 2015 to date. The central endpoint in a higher tier bumble bee study is the colony reproduction success (production of young queens, Cabrera et al. 2016). The endpoint is chosen because at the end of the annual life cycle of a bumble bee colony all workers die and only young queens overwinter. Queens that survive establish a new colony in the following year. However, assessing queen reproduction is challenging. Many variables can influence the number of produced queens, such as the right timing for the termination of the study or the condition of the colony at study start. Furthermore, young queen weights are measured. Weight is used as indicator of diapause survival. Literature values of average weight needed for survival before overwintering state 0.8 g for a young queen for successful overwintering (Beekman et al. 1998). Based on data from ring tests of 2016 and 2017 we tried to answer several open questions concerning queen reproduction, i.e. how can the experimental set-up influence queen weights and how high is the natural variation in queen numbers and queen weight/size?

Effects of queen mating status, pre-diapause weight and pupae’s sex on colony initiation in small-scale rearing of Bombus terrestris

Diapause control and colony initiation are among the major problems encountered in the rearing of bumble bee colonies in small-scale rearing. In this study, we used Bombus terrestris queens obtained from commercial colonies to investigate (1) the diapause survival in virgin and mated queens, (2) the diapause and colony initiation performance of mated bumble bee queens in relation to the pre-diapause weight and (3) the effect of pupae’s sex on colony initiation. We found that diapause survival is negatively affected by mating and by the low pre-diapause weight, but first egg deposition and development of the first adult worker were delayed in heavy queens. We found no significant differences in the egg-laying success in relation to pupae’s sex; however, queens stimulated with queen pupae laid more eggs per cell and developed a first brood larger than those stimulated with male pupae. Our results can be useful in small-scale rearing, including the rearing of wild queens for conservation purposes.

Diapause and winter survival of two Orius species from southern Africa

The cold hardiness and overwintering potential of the southern African pirate bugs, Orius thripoborus (Hesse) and Orius naivashae (Poppius) (Hemiptera: Anthocoridae), were assessed in the laboratory. Diapause traits were studied by observing nymphal development and reproductive performance of adults at 18 °C and three photoperiods (10:14, 12:12 and 14:10 (L:D) h). A 12 h light regime was also tested at 23 °C. A 12 h photoperiod and 18 °C induced reproductive diapause in 84 and 42 % of O. naivashae and O. thripoborus females, respectively. Cold tolerance of adults was measured by determining the supercooling point (SCP, the temperature at which the insect’s body fluids freeze) and lethal time (LT50, the time required to kill 50 % of the population) at 0 and 5 °C. All observed SCPs ranged from −21 to −17 °C. Significantly lower SCP values were observed for acclimated (seven days at 10 °C) O. naivashae females. LT50-values averaged 6.4 and 4.4 days at 0 °C and 11.6 and 7.8 days at 5 °C, for adults of O. thripoborus and O. naivashae, respectively. The findings indicate that O. naivashae is less cold tolerant and has a higher diapause incidence compared with O. thripoborus. Therefore, the latter species may have better potential for use in biological control programmes in the cooler regions of southern Africa or elsewhere.

The effect of overwintering temperature on the body energy reserves and phenoloxidase activity of bumblebee Bombus lucorum queens

Warming winters and changes in species composition related to the estimated global warming may cause a threat to bumblebees adapted to cold winters. During the overwintering period, their intermediary and respiratory metabolism decreases but metabolism remains responsive to temperature. The effect of temperature on diapause survival, phenoloxidase (PO) activity, and energy expenditure of the white-tailed bumblebee (Bombus lucorum) after a 4-month diapause were studied by manipulating the diapause temperature. Two overwintering temperatures were used, cold (1.8 °C) and warm (9 °C). Body fat content was used as an estimate of the remaining energy resources and PO activity as an immune function parameter of overwintering bumblebee queens. The baseline levels of PO activity were used to measure the differences in B. lucorum queen responses after overwintering in either temperature. We found a 0.4 g pre-diapause threshold weight of survival in B. lucorum. Large queens had more fat left and a higher PO activity compared to small ones after overwintering in warm conditions, but in the cold there was no effect of size on the remaining fat in the fat body of queens or their PO activity. The observed difference in energy usage appears to relate to normal size-dependent metabolism and variation in energy allocation between basic metabolism and immune functions.

Effect of different diapause regimes on survival and colony development in the bumble bee, Bombus terrestris

SummaryThe effect of different diapause regimes on diapause survival and post-diapause performance of queens of the bumble bee Bombus terrestris was determined in an attempt to establish optimal diapause condition for mass rearing. Mated queens were randomly divided into four groups and subjected to one of four diapause regimes: anesthetized with CO2 (non hibernated); or hibernated for 45, 75 or 105 days at 4.5 ± 0.5°C and anesthetized with CO2. Queens hibernated for 45 days had the highest survival (80.68%). Survival decreased with increasing duration of diapause. Although non hibernated queens produced significantly more workers, males and queens than the hibernated queens, egg laying rate and colony production (more than 10 workers emerged) rate were much lower in the non hibernated queens than in the hibernated queens. The highest egg laying and colony production rates were found in the 45 days hibernated treatment (90% and 80% respectively). In terms of the lowest diapause mortality and highest post-diapause performance, therefore, hibernating queens for 45 days at 4.5 ± 0.5°C and then anesthetizing them with CO2 appears to be the best diapause regime for mass rearing of B. terrestris.

Ageing is reversed, and metabolism is reset to young levels in recovering dauer larvae of C. elegans

The nematode Caenorhabditis elegans responds to unfavourable environmental conditions by arresting development and entering diapause as a dauer larva. Dauers can survive several times the normal life span and the duration of the dauer state has no effect on postdauer life span. This led to the suggestion that dauers are non-ageing, and that dauers eventually perish as the consequence of depletion of stored nutrients. We have investigated physiological changes associated with long-term diapause survival, and found that dauer larvae slowly develop senescence-like symptoms, including decrease of metabolic capacity, aconitase enzyme activity, and ATP stores, and increase of lipofuscin- and oxidised flavin-specific fluorescence. However, these changes are reversed when the dauers recover. Thus senescence can occur before attainment of reproductive maturity, and furthermore, is reversible. Other life processes, including respiration rate and heat output, remain unaltered over four weeks of diapause at 24 °C. Possible determinants of the enhanced life maintenance include increased resistance to oxidative stress provided by enhanced superoxide dismutase and catalase activities, and a shift to a highly reducing redox status.

Gamma Irradiation Quarantine Treatment Against Blueberry Maggot and Apple Maggot (Diptera: Tephritidae)

The criterion for efficacy of irradiation disinfestation treatments against tephritid fruit flies has been prevention of adult emergence. Although this technique has worked well for tropical tephritids that do not diapause, it is difficult to apply to diapausing insects that must be brought out of diapause by lengthy and not entirely successful procedures. Therefore, a more reliable method of measuring efficacy of irradiation quarantine treatments against diapausing tephritids is needed. Some Tephritidae are known to diapause as phanerocephalic pupae. Accordingly, that would be the latest stage that could be used to determine efficacy without the complications posed by estimating diapause survival. Prevention of the phanerocephalic pupa at the 99% level was accomplished with an estimated 58 and 24 Gy for the apple maggot, Rhagoletis pomonella (Walsh), and the blueberry maggot, Rhagoletis mendax Curran, respectively, when irradiated as 3rd instars in fruits. Adult apple maggot emergence was prevented with an estimated 15 Gy, which was 26% of the dose required to prevent pupation to the complete phanerocephalic stage. Prevention of the phanerocephalic pupa can be determined ≈6 d after pupariation at ambient temperatures, making it possible to adjust research parameters during a limited season, such as when working with the blueberry maggot, which is available in the field in blueberries during late July through early September. Although basing efficacy of irradiation quarantine treatments against diapausing tephritids on prevention of pupation will result in substantially higher doses than basing efficacy on prevention of adult emergence, the research can be done more rapidly and with greater confidence, and many temperate fruits, including blueberries and apples, tolerate much higher radiation doses than those required to prevent pupation of tephritids.

Diapause survival and post‐diapause performance in bumblebee queens (Bombus terrestris)

AbstractDiapause survival and post‐diapause performance (i.e., if a queen starts to lay eggs) of in total 2210 bumblebee queens (Bombus terrestris) were measured under different diapause regimes: 5 temperatures (−5, 0, 5, 10 and 15 °C) in combination with 5 durations of exposure (1, 2, 4, 6 and 8 months).The results show that weight at the start of diapause determines to a large extent whether a queen will be able to survive diapause. Queens with a wet weight below 0.6 g prior to diapause did not survive, but for those queens exceeding this threshold a higher pre‐ diapause weight did not increase their post‐diapause performance.There was no effect of temperature on diapause survival; 76% of the variance in survival could be explained by the duration of the treatment. Neither temperature nor duration of exposure had an effect on post‐diapause performance. The preoviposition period of the queens that laid eggs was also determined. The preoviposition period was affected by both temperature and duration of exposure: the preoviposition period decreased with decreasing temperature but also with increasing duration of the treatment.