Plasticity drives extreme cold tolerance of emerald ash borer (Agrilus planipennis) during a polar vortex

Integrating water balance mechanisms into predictions of insect responses to climate change

Efficient water balance is key to insect success. However, the hygric environment is changing with climate change; although there are compelling models of thermal vulnerability, water balance is often neglected in predictions. Insects survive desiccating conditions by reducing water loss, increasing their total amount of water (and replenishing it) and increasing their tolerance of dehydration. The physiology underlying these traits is reasonably well understood, as are the sources of variation and phenotypic plasticity. However, water balance and thermal tolerance intersect at high temperatures, such that mortality is sometimes determined by dehydration, rather than heat (especially during long exposures in dry conditions). Furthermore, water balance and thermal tolerance sometimes interact to determine survival. In this Commentary, we propose identifying a threshold where the cause of mortality shifts between dehydration and temperature, and that it should be possible to predict this threshold from trait measurements (and perhaps eventually a priori from physiological or -omic markers).

The freeze-avoiding mountain pine beetle (Dendroctonus ponderosae) survives prolonged exposure to stressful cold by mitigating ionoregulatory collapse

Insect performance is linked to environmental temperature, and surviving through winter represents a key challenge for temperate, alpine and polar species. To overwinter, insects have adapted a range of strategies to become truly cold hardy. However, although the mechanisms underlying the ability to avoid or tolerate freezing have been well studied, little attention has been given to the challenge of maintaining ion homeostasis at frigid temperatures in these species, despite this limiting cold tolerance for insects susceptible to mild chilling. Here, we investigated how prolonged exposure to temperatures just above the supercooling point affects ion balance in freeze-avoidant mountain pine beetle (Dendroctonus ponderosae) larvae in autumn, mid-winter and spring, and related it to organismal recovery times and survival. Hemolymph ion balance was gradually disrupted during the first day of exposure, characterized by hyperkalemia and hyponatremia, after which a plateau was reached and maintained for the rest of the 7-day experiment. The degree of ionoregulatory collapse correlated strongly with recovery times, which followed a similar asymptotical progression. Mortality increased slightly during extensive cold exposures, where hemolymph K+ concentration was highest, and a sigmoidal relationship was found between survival and hyperkalemia. Thus, the cold tolerance of the freeze-avoiding larvae of D. ponderosae appears limited by the ability to prevent ionoregulatory collapse in a manner similar to that of chill-susceptible insects, albeit at much lower temperatures. Based on these results, we propose that a prerequisite for the evolution of insect freeze avoidance may be a convergent or ancestral ability to maintain ion homeostasis during extreme cold stress.

Effect of a severe cold spell on overwintering survival of an invasive forest insect pest

Cold temperatures can play a significant role in the range and impact of pest insects. Severe cold events can reduce the size of insect outbreaks and perhaps even cause outbreaks to end. Measuring the precise impact of cold events, however, can be difficult because estimates of insect mortality are often made at the end of the winter season. In late January 2023 long-term climate models predicted a significant cold event to occur over eastern North America. We used this event to evaluate the immediate impact on hemlock woolly adelgid (Adelges tsugae Annand) overwintering mortality at four sites on the northern edge of the insects invaded range in eastern North America. We observed complete mortality, partial mortality and no effects on hemlock woolly adelgid mortality that correlated with the location of populations and strength of the cold event. Our data showed support for preconditioning of overwintering adelgids having an impact on their overwintering survival following this severe cold event. Finally, we compared the climatic conditions at our sites to historical weather data and previous observations of mortality in Nova Scotia. The cold event observed in February 2023 resulted in the coldest temperatures observed at these sites, including the period within which hemlock woolly adelgid invaded, suggesting cold conditions, especially under anthropogenic climate forcing, may not be a limiting factor in determining the ultimate northern range of hemlock woolly adelgid in eastern North America.

Comparative Transcriptome Analysis of Galeruca daurica Reveals Cold Tolerance Mechanisms

Galeruca daurica (Joannis) is a pest species with serious outbreaks in the Inner Mongolian grasslands in recent years, and its larvae and eggs are extremely cold-tolerant. To gain a deeper understanding of the molecular mechanism of its cold-tolerant stress response, we performed de novo transcriptome assembly of G. daurica via RNA-Seq and compared the differentially expressed genes (DEGs) of first- and second-instar larvae grown and developed indoors and outdoors, respectively. The results show that cold tolerance in G. daurica is associated with changes in gene expression mainly involved in the glycolysis/gluconeogenesis pathway, the fatty acid biosynthesis pathway and the production of heat shock proteins (HSPs). Compared with the control group (indoor), the genes associated with gluconeogenesis, fatty acid biosynthesis and HSP production were up-regulated in the larvae grown and developed outdoors. While the changes in these genes were related to the physiological metabolism and growth of insects, it was hypothesized that the proteins encoded by these genes play an important role in cold tolerance in insects. In addition, we also investigated the expression of genes related to the metabolic pathway of HSPs, and the results show that the HSP-related genes were significantly up-regulated in the larvae of G. daurica grown and developed outdoors compared with the indoor control group. Finally, we chose to induce significant expression differences in the Hsp70 gene (Hsp70A1, Hsp70-2 and Hsp70-3) via RNAi to further illustrate the role of heat stress proteins in cold tolerance on G. daurica larvae. The results show that separate and mixed injections of dsHSP70A1, dsHsp70-2 and dsHsp70-3 significantly reduced expression levels of the target genes in G. daurica larvae. The super-cooling point (SCP) and the body fluid freezing point (FP) of the test larvae were determined after RNAi using the thermocouple method, and it was found that silencing the Hsp70 genes significantly increased the SCP and FP of G. daurica larvae, which validated the role of heat shock proteins in the cold resistance of G. daurica larvae. Our findings provide an important theoretical basis for further excavating the key genes and proteins in response to extremely cold environments and analyzing the molecular mechanism of cold adaptation in insects in harsh environments.

Meta-analysis reveals less sensitivity of non-native animals than natives to extreme weather worldwide

Extreme weather events (EWEs; for example, heatwaves, cold spells, storms, floods and droughts) and non-native species invasions are two major threats to global biodiversity and are increasing in both frequency and consequences. Here we synthesize 443 studies and apply multilevel mixed-effects metaregression analyses to compare the responses of 187 non-native and 1,852 native animal species across terrestrial, freshwater and marine ecosystems to different types of EWE. Our results show that marine animals, regardless of whether they are non-native or native, are overall insensitive to EWEs, except for negative effects of heatwaves on native mollusks, corals and anemone. By contrast, terrestrial and freshwater non-native animals are only adversely affected by heatwaves and storms, respectively, whereas native animals negatively respond to heatwaves, cold spells and droughts in terrestrial ecosystems and are vulnerable to most EWEs except cold spells in freshwater ecosystems. On average, non-native animals displayed low abundance in terrestrial ecosystems, and decreased body condition and life history traits in freshwater ecosystems, whereas native animals displayed declines in body condition, life history traits, abundance, distribution and recovery in terrestrial ecosystems, and community structure in freshwater ecosystems. By identifying areas with high overlap between EWEs and EWE-tolerant non-native species, we also provide locations where native biodiversity might be adversely affected by their joint effects and where EWEs might facilitate the establishment and/or spread of non-native species under continuing global change.

An integrative phenology and climatic suitability model for emerald ash borer

Introduction

Decision support models that predict both when and where to expect emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), are needed for the development and implementation of effective management strategies against this major invasive pest of ash (Fraxinus species) in North America and other regions such as Europe. We present a spatialized model of phenology and climatic suitability for EAB for use in the Degree-Days, Risk, and Phenological event mapping (DDRP) platform, which is an open-source decision support tool to help detect, monitor, and manage invasive threats.

Methods

We evaluated the model using presence records from three geographic regions (China, North America, and Europe) and a phenological dataset consisting primarily of observations from the northeastern and midwestern United States. To demonstrate the model, we produced phenological event maps for a recent year and tested for trends in EAB's phenology and potential distribution over a recent 20-year period.

Results

Overall, the model exhibited strong performance. Presence was correctly estimated for over 99% of presence records and predicted dates of adult phenological events corresponded closely with observed dates, with a mean absolute error of ca. 7 days and low estimates of bias. Climate stresses were insufficient to exclude EAB from areas with native Fraxinus species in North America and Europe; however, extreme weather events, climate warming, and an inability for EAB to complete its life cycle may reduce suitability for some areas. Significant trends toward earlier adult emergence over 20 years occurred in only some areas.

Discussion

Near real-time model forecasts for the conterminous United States are available at two websites to provide end-users with decision-support for surveillance and management of this invasive pest. Forecasts of adult emergence and egg hatch are particularly relevant for surveillance and for managing existing populations with pesticide treatments and parasitoid introductions.

Predicting Emerald Ash Borer Adult Emergence and Peak Flight Activity in Winnipeg, Manitoba, Canada

The invasive emerald ash borer (Agrilus planipennis Fairmaire; Coleoptera: Buprestidae) has killed tens of millions of ash (Fraxinus spp.) trees across North America. A. planipennis was first detected in Winnipeg, Manitoba in 2017 and has the potential to become a serious threat to the city's ash canopy which accounts for ~30% of the public tree inventory. The goal of this study was to predict when adult A. planipennis emergence and peak activity would occur in Winnipeg to help logistical planning for the implementation of a city-wide management program. The management program would focus on detection and limiting the spread of the beetle with the objective of preserving ash trees as long as possible allowing for more proactive management of the EAB infestation. To predict adult emergence and peak activity of A. planipennis, we used local weather station data to calculate the number of degree-days accumulated in each year for the 1970–2019 period using three different degree-day accumulation models. Developmental thresholds for A. planipennis were derived from previous North American studies. The estimated mean emergence dates for the 50-year period were June 14 ± 8.5 days (double sine model), June 14 ± 8.5 days (single sine model), and June 19 ± 9.1 days (standard model) whereas the peak activity dates were July 16 ± 8.8 days (double sine model), July 17 ± 8.7 days (single sine model), and July 21 ± 9.4 days (standard model). Meteorological records indicate that temperatures in the Winnipeg region have increased over the study period. However, our predicted emergence dates do not significantly differ over the 50 years examined in the study, although estimated peak activity dates are significantly earlier, suggesting that EAB movement may benefit from climate change. The results from this study will provide managers with information regarding the temporal behavior of A. plannipennis in Winnipeg allowing for improved timing of control measures and monitoring, thereby extending the projected life span of a significant ash tree population within the Winnipeg urban region. The management model developed for Winnipeg could serve as an example for other locations in the prairie region of North America.

Southern Range Expansion of the Emerald Ash Borer, Agrilus planipennis, in Russia Threatens Ash and Olive Trees in the Middle East and Southern Europe

Agrilus planipennis (Coleoptera: Buprestidae) is the most serious invasive pest of ash trees (Fraxinus spp., Oleaceae) in the world. It has not yet reached the range of olive tree plantations, however it has been shown to complete its life cycle in this host tree. This pest is native to East Asia was first found in Europe in Moscow in 2003 and has been spreading ever since. The aims of this study were to determine if the southern border of the range has already reached the Caucasus and to assess the potential range in this region based on host availability and heat availability. In 2021, we surveyed ash trees south to the known range in Russia. We did not find the pest in six cities in the North Caucasus region but found it in the city of Azov close to the Caucasus. Analysis of information about 550 localities of ash trees in the Caucasus showed that Fraxinus spp. is common throughout the region. The calculation of annual growing degree days base 10 °C indicated that the places where Fraxinus spp. grow above 1500 m are too cold for A. planipennis and therefore could potentially become a refuge for ash trees. The spread of A. planipennis to the Caucasus is of concern. First, the forest ecosystems of this region are endangered, since European ash Fraxinus excelsior is much more common there than in the currently infested regions in Russia. Second, the Russian Caucasus can become the gateway to Georgia, Armenia, Azerbaijan, Turkey and other countries of the Middle East and Southern Europe. We propose using Fraxinus angustifolia, F. ornus and Olea europaea growing in the Caucasus and adjacent regions as sentinel trees for the monitoring and pest risk assessment of these tree species.