Thermal regimes of aquatic ecosystems are predicted to change as climate warming progresses over the next century, with high-latitude and high-elevation regions predicted to be particularly impacted. Here, we have modelled alpine stream water temperatures from air temperature data and used future predicted air temperature trajectories (representative concentration pathway [rcp] 4.5 and 8.5) to predict future water temperatures. Modelled stream water temperatures have been used to calculate cumulative degree days (CDDs) under current and future climate conditions. These calculations show that degree days will accumulate more rapidly under the future climate scenarios, and with a stronger effect for higher CDD values (e.g., rcp 4.5: 18-28 days earlier [CDD = 500]; 42-55 days earlier [CDD = 2000]). Changes to the time to achieve specific CDDs may have profound and unexpected consequences for alpine ecosystems. Our calculations show that while the effect of increased CDDs may be relatively small for organisms that emerge in spring-summer, the effects for organisms emerging in late summer-autumn may be substantial. For these organisms, the air temperatures experienced upon emergence could reach 9°C (rcp 4.5) or 12°C (rcp 8.5) higher than under current climate conditions, likely impacting on the metabolism of adults, the availability of resources, including food and suitable oviposition habitat, and reproductive success. Given that the movement of aquatic fauna to the terrestrial environment represents an important flux of energy and nutrients, differential changes in the time periods to achieve CDDs for aquatic and terrestrial fauna may de-couple existing predator-prey interactions.

The impacts of climate change on the development of insects are of great concern due to potential alterations in population dynamics and pest pressure. The carrot weevil, Listronotus oregonensis, is a major agricultural pest, and its development is influenced by temperature and photoperiod. In this study, our aim was to investigate the impact of temperature increases on the voltinism and reproductive diapause of the carrot weevil under field conditions and bioclimatic models. Field observations were conducted over two growing seasons using structures that allowed for temperature increases. The developmental stages of the carrot weevil, including female reproductive status, oviposition and larval stage, were monitored weekly to measure the proportion of individuals undergoing an additional generation. Concurrently, bioclimatic models were used to simulate the probability of a second generation under current (1981-2010) and future (2041-2070) climates, considering a lower and a higher change in emission scenarios. Results showed that rising temperatures led to an increase in the proportion of carrot weevils undergoing inhibition of the reproductive diapause and a higher number of eggs laid in the field. The models indicated a substantial rise in the probability of a second generation developing, from 24% to 37% to 62%-99% under current and future climates, respectively. These findings demonstrate the potential for significant alterations in carrot weevil population dynamics, resulting in increased pest pressure on crops. Further research is needed to fully understand the implications of these findings and to develop effective adaptation measures to mitigate the negative impacts of global warming on insect populations and agriculture.

Herbivorous insects having variable numbers of generations annually depending on climate and day length conditions are increasingly breeding additional generations driven by elevated temperature under the scenario of global warming, which will increase insect abundance and result in more frequent damage events. Theoretically, this relies on two premises, i.e., either an evolutionary shift to facultative diapause for an insect behaving an obligatory diapause or developmental plasticity to alter voltinism productively for an insect with facultative diapause before shortening photoperiods inducing diapause. Inter-population evidence supporting the premise (theory) comes primarily from a model system with voltinism linked to thermal gradients across latitude. We examined the intra-population evidence in the field (47°24\' N, 123°68\' E) with Ostrinia furnacalis, one of the most destructive pests, on corn in Asia and Pacific islands. The species was univoltine in high latitudinal areas (≤46° N). Divergence of the diapause feature (obligatory and facultative) was observed within the field populations from 2016 to 2021. Warmer climates would provoke more facultative diapause individuals to initiate a second generation, which will significantly drive the population to evolve toward facultative diapause (multi-voltinism). Both divergent diapause and temperature must be considered for accurate prediction of phenology and population dynamics in ACB.

We used European geometrid moths (>630 species) as a model group to investigate how life history traits linked to larval host plant use (i.e., diet breadth and host-plant growth form) and seasonal life cycle (i.e., voltinism, overwintering stage and caterpillar phenology) are related to adult body size in holometabolous insect herbivores. To do so, we applied phylogenetic comparative methods to account for shared evolutionary history among herbivore species. We further categorized larval diet breadth based on the phylogenetic structure of utilized host plant genera. Our results indicate that species associated with woody plants are, on average, larger than herb feeders and increase in size with increasing diet breadth. Obligatorily univoltine species are larger than multivoltine species, and attain larger sizes when their larvae occur exclusively in the early season. Furthermore, the adult body size is significantly smaller in species that overwinter in the pupal stage compared to those that overwinter as eggs or caterpillars. In summary, our results indicate that the ecological niche of holometabolous insect herbivores is strongly interrelated with body size at maturity.

The Asian corn borer (ACB) Ostrinia furnacalis (Guenée) can occur in one to seven generations annually from cool (48°00\' N) to warm (18°10\' N) region of corn cultivation in China. Although ACB is commonly known as a facultative larval diapause insect, the co-existence of various voltinism suggests that intra-population variation may have evolved for the nature of diapause, i.e., voltinism plasticity. Here, we conducted recurrent selection efforts to establish three strains of, respectively, univoltine (with obligate diapause), multivoltine (with facultative diapause), and non-diapausing ACB under various temperature and photoperiod environments. The univoltine (Lu) strain has evolved a stable univoltinism under a diapause suppressing condition (16 h daylength at 28 °C), with the diapause incidence constantly over 80% after three generations of selection. The multivoltine strain (Lm) under the high temperature (28 °C) was shown to have a typical facultative diapause induced by a range of short-day lengths (11-13.5 h). Diapause incidence was constantly <2.6% under the long day length (16 h) when the temperature was from 18 to 28 °C, i.e., low temperature could not enhance the diapause response in the Lm strain. However, the development was prolonged from 14.2 ± 0.3 d to 46.0 ± 0.8 d when the temperature was reduced from 28 °C to 18 °C. The majority (94.4%) of the developed Ln strain still maintained the non-diapausing nature under a diapause enhancing condition, i.e., a short (13 h) daylength at a low temperature (22 °C). Lm and Ln were able to complete their second generation in Heihe (50°14\' N) if the first-generation moth oviposits before 18 June. The study suggests that ACB has evolutionary intra-population variation in voltinism. Under the climate change scenario warmer spring and summer might affect the proportion of sympatric voltine biotype populations that evolve toward being multivoltine.

The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), has killed millions of ash (Fraxinus spp.) trees across North America. Classical biological control using introductions of parasitoid wasps may provide a sustainable approach to managing this invasive insect. However, the establishment of parasitoids in the southern United States has been difficult. The phenology of emerald ash borer was studied in central North Carolina to inform biological control efforts that better align with the seasonal availability of susceptible emerald ash borer life stages in the warm climate of this region. Biweekly emerald ash borer life stage assessments were conducted in stands of infested green ash (Fraxinus pennsylvanica Marshall, Lamiales: Oleaceae) over 26 consecutive months (June 2019 through August 2021). Adult trapping was also conducted in these stands in the spring and summer of 2019, 2020, and 2021. Based on these collections, emerald ash borer exhibits a univoltine (1-yr) life cycle. Parasitoid-susceptible larvae (third and fourth instars in galleries) are present from late June through October (~1,100-3,000 degree days base 10ºC) and are mostly absent during the remainder of the year. Parasitoid release timings and the life history of selected parasitoid species should be aligned with this window of host availability to be effective. This characterization of emerald ash borer phenology and voltinism will help improve the timing and effectiveness of management efforts as this forest pest continues to spread in southern North America.

In the last decade, the invasive brown marmorated stink bug Halyomorpha halys, native to East Asia, has become one of the most serious pests for agricultural crops worldwide. First detected in Europe (in Switzerland), the insect is now widely found across the European continent and many Eurasian countries. Since its first appearance in Slovenia in 2017 it has caused considerable damage to fruit and vegetable production. Understanding the biology and behavior in the local environmental conditions is of key importance for an effective pest management. Knowledge of the voltinism of the species is crucial to anticipate critical phases of pest development and for adapting control measures that target the vulnerable life stages of the pest. A 3-year study (2019-2021) of H. halys biological parameters was performed outdoors in Nova Gorica (western Slovenia), confirming that in the sub-Mediterranean climate this pest has two overlapping generations per year. The net reproductive rates observed in the studied period indicate growing populations. The highest population growth was recorded in 2019, when the net reproductive rate of increase (R0) reached 14.84 for the summer generation and 5.64 for the overwintering generation. These findings match the current situation in Slovenia, where increasing populations of H. halys and severe crop damage have been observed since 2019.

Climate change has been shown to advance spring phenology, increase the number of insect generations per year (multivoltinism) and increase pathogen infection levels. However, we lack insights into the effects of plant spring phenology and the biotic environment on the preference and performance of multivoltine herbivores and whether such effects extend into the later part of the growing season. To this aim, we used a multifactorial growth chamber experiment to examine the influence of spring phenology on plant pathogen infection, and how the independent and interactive effects of spring phenology and plant pathogen infection affect the preference and performance of multigenerational attackers (the leaf miner Tischeria ekebladella and the aphid Tuberculatus annulatus) on the pedunculate oak in the early, mid and late parts of the plant growing season. Pathogen infection was highest on late phenology plants, irrespective of whether inoculations were conducted in the early, mid or late season. The leaf miner consistently preferred to oviposit on middle and late phenology plants, as well as healthy plants, during all parts of the growing season, whereas we detected an interactive effect between spring phenology and pathogen infection on the performance of the leaf miner. Aphids preferred healthy, late phenology plants during the early season, healthy plants during the mid season, and middle phenology plants during the late season, whereas aphid performance was consistently higher on healthy plants during all parts of the growing season. Our findings highlight that the impact of spring phenology on pathogen infection and the preference and performance of insect herbivores is not restricted to the early season, but that its imprint is still present - and sometimes equally strong - during the peak and end of the growing season. Plant pathogens generally negatively affected herbivore preference and performance, and modulated the effects of spring phenology. We conclude that spring phenology and pathogen infection are two important factors shaping the preference and performance of multigenerational plant attackers, which is particularly relevant given the current advance in spring phenology, pathogen outbreaks and increase in voltinism with climate change.

Under climate warming, temperate ectotherms are expected to hatch earlier and grow faster, increase the number of generations per season, i.e., voltinism. Here, we studied, under laboratory conditions, the impact of artificial warming and manipulated hatching dates on life history (voltinism, age and mass at emergence and growth rate) and physiological traits (phenoloxidase (PO) activity at emergence, as an indicator of investment in immune function) and larval survival rate in high-latitude populations of the damselfly Ischnura elegans. Larvae were divided into four groups based on crossing two treatments: early versus late hatching dates and warmer versus control rearing temperature. Damselflies were reared in groups over the course of one (univoltine) or two (semivoltine) growth seasons, depending on the voltinism. Warming temperature did not affect survival rate. However, warming increased the number of univoltine larvae compared to semivoltine larvae. There was no effect of hatching phenology on voltinism. Early hatched larvae reared under warming had elevated PO activity, regardless of their voltinism, indicating increased investment in immune function against pathogens. Increased PO activity was not associated with effects on age or mass at emergence or growth rate. Instead, life history traits were mainly affected by temperature and voltinism. Warming decreased development time and increased growth rate in univoltine females, yet decreased growth rate in univoltine males. This indicates a stronger direct impact of warming and voltinism compared to impacts of hatching phenology on life history traits. The results strengthen the evidence that phenological shifts in a warming world may affect physiology and life history in freshwater insects.

Studies on the phenology of local populations of invasive insects are necessary for monitoring and predicting their dispersion. We investigated the phenology of the brown marmorated stink bug, Halyomorpha halys, in the Sochi region (Krasnodar Territory, Russia) from 2018 to 2021 by regular field sampling and dissecting. The results of the sampling suggest that H. halys is at least partially bivoltine in the studied region: the main period of mass oviposition (by the overwintered females) occurs from June to July; the second, much shorter period of egg-laying (by females of the new, i.e., the first generation) occurs in August. Reproductively active individuals (i.e., females with developed ovaries and filled spermatheca and males with filled ectodermal sac) were recorded from the end of May to the beginning of September. Such a seasonal pattern correlated with day length: when the natural photoperiod decreased below the experimentally determined critical day length (15.0−15.5 h), the proportions of females with fully developed ovaries sharply dropped to zero. Both the rate of H. halys pre-adult development and the timing of the induction of winter adult diapause observed under natural conditions fully agreed with the earlier predictions that had been based on the results of laboratory experiments.