Century-long butterfly range expansions in northern Europe depend on climate, land use and species traits

Characterisation of riverine mosquito (Diptera: Culicidae) community structure in southern Australia and the impact of a major flood based on analysis of a 20-year dataset

We investigated the mosquito community along 315 km of the Murray River, where we identified three assemblages (upper, middle, and lower river) that exhibited different patterns of species richness and diversity over 20 years. In the lower reaches (i.e., more southern latitudes), species richness and community diversity declined over time, while there was no significant change in either the middle or upper reaches. While the overall mean abundance of the common, pathogen-carrying mosquito (Diptera: Culicidae) species Aedes camptorhynchus Thomson, increased in the lower river but declined in the upper river. These results provide important information on the diversity and abundance of mosquito communities adjacent to the Murray River and highlight the importance of considering spatial and temporal variation when assessing the risk of mosquito-borne diseases. Furthermore, data presented here illustrate that there the common public narrative around increasing mosquito abundance and geographic expansion under climate change is not universally true.

Species responses to weather anomalies depend on local adaptation and range position

Species show intra-specific variation in responses to climate change linked to adaptation to the local climatic conditions. Likewise, species are expected to be more resilient to climate change at the centre of their bioclimatic niche, but this pattern is not general. We show that species sensitivity to climatic anomalies varies with local adaptation and the position in the bioclimatic niche, using long-term butterfly monitoring data for 34 species. Climatic anomalies negatively affected all populations of locally adapted species. Globally adapted species were positively or negatively affected by climatic anomalies, depending on population location and direction of anomalies. These responses impacted population trends as globally adapted species showed steeper declines at the trailing margin. Surprisingly, locally adapted species showed stable abundances at the trailing margin, but declines at the leading; which could be explained by the with the 'warmer is better' hypothesis where thermodynamics limit insect performance at cooler conditions.

Is temporal synchrony necessary for effective Batesian mimicry?

Batesian mimicry occurs when palatable mimics gain protection from predators by evolving a phenotypic resemblance to an aposematic model species. While common in nature, the mechanisms maintaining mimicry are not fully understood. Patterns of temporal synchrony (i.e. temporal co-occurrence) and model first occurrence have been observed in several mimicry systems, but the hypothesis that predator foraging decisions can drive the evolution of prey phenology has not been experimentally tested. Here, using phenotypically accurate butterfly replicas, we measured predation rates on the chemically defended model species Battus philenor and its imperfect Batesian mimic Limenitis arthemis astyanax under four different phenological conditions to understand the importance of temporal synchrony and model first occurrence in mimicry complexes. We predicted that protection for mimics increases when predators learn to avoid the models' aposematic signal right before encountering the mimic, and that learned avoidance breaks down over time in the model's absence. Surprisingly, we found that asynchronous model first occurrence, even on short time scales, did not provide increased protection for mimics. Mimics were only protected under conditions of temporal synchrony, suggesting that predators rely on current information, not previously learned information, when making foraging decisions.

Effects of temperature experienced across life stages on morphology and flight behavior of painted lady butterflies (Vanessa cardui)

BACKGROUND

With ongoing anthropogenic climate change, there is increasing interest in how organisms are affected by higher temperatures, including how animals respond behaviorally to increasing temperatures. Movement behavior is especially relevant, as the ability of a species to shift its range is implicitly dependent upon movement capacity and motivation. Temperature may influence movement behavior of ectotherms both directly, through an increase in body temperature, and indirectly, through temperature-dependent effects on physiological and morphological traits.

METHODS

We investigated the influence of ambient temperature during two life stages, larval and adult, on body size and movement behavior of the painted lady butterfly (Vanessa cardui). We reared painted ladies to emergence at either a "low" (24 °C) or "high" (28 °C) temperature. At eclosion, we assessed flight behavior in an arena test. We used a full factorial experimental design in which half of the adults that emerged from each rearing treatment were tested at either the "low" or "high" temperature. We measured adult body size, including wingspan, and determined flight speed, distance, and duration from video recordings.

RESULTS

Adult butterflies that experienced the higher temperature during development were larger. We documented an interaction of rearing x testing temperature on flight behavior: unexpectedly, the fastest butterflies were those who experienced a change in temperature, whether an increase or decrease, between rearing and testing. Individuals that experienced matching thermal environments flew more slowly, but for more time and covering more distance. We found no influence of body size per se on flight.

CONCLUSIONS

We conclude that the potential role of "matching" thermal environments across life stages has been underinvestigated with regard to how organisms may respond to warming conditions.

Seasonality of forest insects: why diapause matters

Insects have major impacts on forest ecosystems, from herbivory and soil-nutrient cycling to killing trees at a large scale. Forest insects from temperate, tropical, and subtropical regions have evolved strategies to respond to seasonality; for example, by entering diapause, to mitigate adversity and to synchronize lifecycles with favorable periods. Here, we show that distinct functional groups of forest insects; that is, canopy dwellers, trunk-associated species, and soil/litter-inhabiting insects, express a variety of diapause strategies, but do not show systematic differences in diapause strategy depending on functional group. Due to the overall similarities in diapause strategies, we can better estimate the impacts of anthropogenic change on forest insect populations and, consequently, on key ecosystems.

Exploring Biodiversity through the Lens of Knautia arvensis Pollinators: Knautia Pollinator Walks as a Monitoring Method

Declining populations of native pollinators, especially wild bees, underline the urgent need for effective monitoring within agricultural ecosystems. This study aims to (i) establish the 'Knautia Pollinator Walk' as an innovative pollinator monitoring method, (ii) examine the link between pollinator richness/density and land cover, and (iii) assess if specialist solitary bees indicate pollinator abundance and morphogroup richness. The approach involves surveying 500 Knautia arvensis inflorescences per site thrice per season. Observations of 11,567 pollinators across 203 taxa showed significant correlations between pollinator diversity and land use. Pollinator populations fluctuated with land cover type, increasing in open areas but decreasing or stabilising in forested and shrubby regions. Noteworthy differences in pollinator types were seen between Russia (solitary bees, small Diptera, Lepidoptera) and Sweden (bumblebees, beetles, furry Diptera). The "Knautia Pollinator Walk" shows promising signs of being an effective tool for monitoring spatiotemporal biodiversity trends. The method offers a scalable approach to pollinator monitoring, which is essential for developing conservation strategies and supporting pollinator populations.

Effects of nocturnal celestial illumination on high-flying migrant insects

Radar networks hold great promise for monitoring population trends of migrating insects. However, it is important to elucidate the nature of responses to environmental cues. We use data from a mini-network of vertical-looking entomological radars in the southern UK to investigate changes in nightly abundance, flight altitude and behaviour of insect migrants, in relation to meteorological and celestial conditions. Abundance of migrants showed positive relationships with air temperature, indicating that this is the single most important variable influencing the decision to initiate migration. In addition, there was a small but significant effect of moonlight illumination, with more insects migrating on full moon nights. While the effect of nocturnal illumination levels on abundance was relatively minor, there was a stronger effect on the insects' ability to orientate close to downwind: flight headings were more tightly clustered on nights when the moon was bright and when cloud cover was sparse. This indicates that nocturnal illumination is important for the navigational mechanisms used by nocturnal insect migrants. Further, our results clearly show that environmental conditions such as air temperature and light levels must be considered if long-term radar datasets are to be used to assess changing population trends of migrants. This article is part of the theme issue 'Towards a toolkit for global insect biodiversity monitoring'.

Upward and Poleward (but Not Phenological) Shifts in a Forest Tenebrionid Beetle in Response to Global Change in a Mediterranean Area

There is an increasing volume of literature on the impact of climate change on insects. However, there is an urgent need for more empirical research on underrepresented groups in key areas, including species for which the effects of climatic change may seem less evident. The present paper illustrates the results of a study on a common forest tenebrionid beetle, Accanthopus velikensis (Piller and Mitterpacher, 1783), at a regional scale within the Mediterranean basin. Using a large set of records from Latium (central Italy), changes in the median values of elevation, latitude, longitude, and phenology between two periods (1900-1980 vs. 1981-2022) were tested. Records of A. velikensis in the period 1981-2022 showed median values of elevation and latitude higher than those recorded in the first period. Thus, in response to rising temperatures, the species became more frequent at higher elevation and in northern places. By contrast, A. velikensis does not seem to have changed its activity pattern in response to increased temperatures, but this might be an artifact due to the inclusion of likely overwintering individuals. The results obtained for A. velikensis indicate that even thermally euryoecious species can show changes in their elevational and latitudinal distribution, and that poleward shifts can be apparent even within a small latitudinal gradient.

Anthropogenic Influence on Moth Populations: A Comparative Study in Southern Sweden

As moths are vital components of ecosystems and serve as important bioindicators, understanding the dynamics of their communities and the factors influencing these dynamics, such as anthropogenic impacts, is crucial to understand the ecological processes. Our study focuses on two provinces in southern Sweden, Västergötland and Småland, where we used province records from 1974 to 2019 in combination with light traps (in 2020) to record the presence and abundance of moth species, subsequently assessing species traits to determine potential associations with their presence in anthropogenically modified landscapes. This study design provides a unique opportunity to assess temporal changes in moth communities and their responses to shifts in environmental conditions, including anthropogenic impacts. Across the Västergötland and Småland provinces in Sweden, we recorded 776 moth taxa belonging to fourteen different taxonomic families of mainly Macroheterocera. We captured 44% and 28% of the total moth species known from these provinces in our traps in Borås (Västergötland) and Kalmar (Småland), respectively. In 2020, the species richness and abundance were higher in Borås than in Kalmar, while the Shannon and Simpson diversity indices revealed a higher species diversity in Kalmar. Between 1974 and 2019, the colonisation rates of the provinces increased faster in Småland. Ninety-three species were found to have colonised these provinces since 1974, showing that species richness increased over the study period. We reveal significant associations between the probability of a species being present in the traps and distinct traits compared to a provincial species pool. Traits over-represented in the traps included species with a high variation in colour patterns, generalist habitat preferences, extended flight periods, lower host plant specificity, and overwintering primarily as eggs. Our findings underscore the ongoing ecological filtering that favours certain species-specific traits. This study sheds light on the roles of climate change and anthropogenic impacts in shaping moth biodiversity, offers key insights into the ecological processes involved, and can guide future conservation efforts.