Day-flying lepidoptera larvae have a poorer ability to thermoregulate than adults.

Changes to ambient temperatures under climate change may detrimentally impact small ectotherms that rely on their environment for thermoregulation; however, there is currently a limited understanding of insect larval thermoregulation. As holometabolous insects, Lepidoptera differ in morphology, ecology and behaviour across the life cycle, and so it is likely that adults and larvae differ in their capacity to thermoregulate. In this study, we investigated the thermoregulatory capacity (buffering ability) of 14 species of day-flying Lepidoptera, whether this is influenced by body length or gregariousness, and whether it differs between adult and larval life stages. We also investigated what thermoregulation mechanisms are used: microclimate selection (choosing locations with a particular temperature) or behavioural thermoregulation (controlling temperature through other means, such as basking). We found that Lepidoptera larvae differ in their buffering ability between species and body lengths, but gregariousness did not influence buffering ability. Larvae are worse at buffering themselves against changes in air temperature than adults. Therefore Lepidoptera may be more vulnerable to adverse temperature conditions during their larval life stage. Adults and larvae rely on different thermoregulatory mechanisms; adults primarily use behavioural thermoregulation, whereas larvae use microclimate selection. This implies that larvae are highly dependent on the area around their foodplant for effective thermoregulation. These findings have implications for the management of land and species, for example, highlighting the importance of creating and preserving microclimates and vegetation complexity surrounding Lepidoptera foodplants for larval thermoregulation under future climate change.

Thermoregulatory ability and mechanism do not differ consistently between neotropical and temperate butterflies.

Climate change is a major threat to species worldwide, yet it remains uncertain whether tropical or temperate species are more vulnerable to changing temperatures. To further our understanding of this, we used a standardised field protocol to (1) study the buffering ability (ability to regulate body temperature relative to surrounding air temperature) of neotropical (Panama) and temperate (the United Kingdom, Czech Republic and Austria) butterflies at the assemblage and family level, (2) determine if any differences in buffering ability were driven by morphological characteristics and (3) used ecologically relevant temperature measurements to investigate how butterflies use microclimates and behaviour to thermoregulate. We hypothesised that temperate butterflies would be better at buffering than neotropical butterflies as temperate species naturally experience a wider range of temperatures than their tropical counterparts. Contrary to our hypothesis, at the assemblage level, neotropical species (especially Nymphalidae) were better at buffering than temperate species, driven primarily by neotropical individuals cooling themselves more at higher air temperatures. Morphology was the main driver of differences in buffering ability between neotropical and temperate species as opposed to the thermal environment butterflies experienced. Temperate butterflies used postural thermoregulation to raise their body temperature more than neotropical butterflies, probably as an adaptation to temperate climates, but the selection of microclimates did not differ between regions. Our findings demonstrate that butterfly species have unique thermoregulatory strategies driven by behaviour and morphology, and that neotropical species are not likely to be more inherently vulnerable to warming than temperate species.

El calentamiento global es una gran amenaza para las especies alrededor del mundo, sin embargo, no se tiene bien definido sí en los insectos, las especies distribuídas en las zonas tropicales son más vulnerables a los cambios de temperature que las especies de zonas templadas o viceversa. Para responder a este interrogante, utilizamos un protocolo de campo estandarizado aplicado a especies de mariposas distribuídas en zonas tropicales (Panamá) versus zonas templadas (Reino Unido, República Checa y Austria), con el cual buscamos: (1) Evaluar la capacidad de amortiguación (capacidad de regular la temperatura corporal en relación con la temperatura del aire circundante) en el a nivel de ensamblaje y familia, (2) Determinar sí las diferencias en la capacidad de amortiguación es facilitada por sus características morfológicas, y (3) Investigar cómo las mariposas usan los microclimas y el comportamiento para termorregularse a tráves de mediciones de temperatura ecológicamente relevantes. Nuestra hipotesis incial soportaba que las mariposas templadas estaban adaptadas para amortiguar los cambios de temperatura en comparación con las mariposas neotropicales, ya que las especies templadas experimentan un rango más amplio de temperaturas que sus contrapartes tropicales. Contrariamente a nuestra hipótesis, a nivel de ensamble, las especies neotropicales (especialmente familia Nymphalidae) fueron mejores en la capaicidad de amortiguacion que las especies templadas, explicado por el hecho de que individuos se enfrían más a altas temperaturas del aire. Así, la morfología fué el principal impulsor de las diferencias en la capacidad de amortiguación entre las especies neotropicales y templadas en comparación con el ambiente térmico experimentado por las mismas. Encontramos que las mariposas templadas utilizaron la termorregulación de postura para elevar su temperatura corporal más que las mariposas neotropicales, probablemente como una adaptación a los climas templados, aunque la selección de microclimas no difirió entre regiones. Nuestros hallazgos demuestran que las especies de mariposas tienen estrategias de termorregulación únicas, impulsadas principalmente por el comportamiento y morfología, además nuestros resultados demuestran que a diferencia de lo que se ha pensado, las especies neotropicales son igual de vulnerables al calentamiento de su hábitat que las especies templadas.

Oviposition behaviour and emergence through time of the small blue butterfly (Cupido minimus) in a nature reserve in Bedfordshire, UK.

ABSTRACT: Climate change affects butterflies in many ways, influencing the timing of emergence and reproduction, habitat preferences, and behaviour. The small blue (Cupido minimus Fuessley, 1775) is highly specialised in its host plant requirements, feeding on the seeds of a single species, kidney vetch (Anthyllis vulneraria), on which the larvae occur singly to avoid cannibalism. The butterfly is likely to be vulnerable to temperature-related changes in oviposition, adult emergence, and host plant flowering times, and is, therefore, a good model species for investigating climate change-related impacts. Using 26 years of data from the national UK Butterfly Monitoring Scheme (1993-2019) from one nature reserve, and 4 years of targeted egg searches (2006, 2007, 2008, 2020) from three reserves in Bedfordshire, UK, we investigated the effects of local temperature on small blue emergence date and total abundance, whether flowerhead or local environmental characteristics predicted small blue oviposition behaviour, and whether this changed between years. Small blue adults emerged on earlier dates over time, and earlier in years with higher maximum February temperatures. Total adult abundance was not predicted by monthly temperatures or total abundance in the previous year. Oviposition behaviour was broadly consistent across years, with egg presence more likely and egg abundance higher on kidney vetch flowerheads that were taller than the surrounding vegetation, and surrounded by taller vegetation and fewer mature flowerheads. The effect of solar radiation differed between years, with a negative effect on the probability of egg presence in 2007 and 2008, but a positive effect in 2020. Egg abundance per flowerhead was highly variable between years, with 2006 having four times more eggs per flowerhead than other years. This was likely driven by high adult abundance in 2006, which could have increased competition for flowerheads. IMPLICATIONS FOR INSECT CONSERVATION: Our results indicate that management for greater availability of taller kidney vetch amongst taller vegetation would encourage small blue oviposition on a greater number of flowerheads, providing a possible means of reducing competition and increasing larval survival, and that this would be effective despite variation in adult abundance between years. The high level of competition we observed in the year with the highest adult abundance indicates that higher numbers of host plants should be encouraged to reduce competition and larval cannibalism in peak years, increasing the likelihood of long-term population persistence and growth. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10841-021-00360-5.

How butterflies keep their cool: Physical and ecological traits influence thermoregulatory ability and population trends.

Understanding which factors influence the ability of individuals to respond to changing temperatures is fundamental to species conservation under climate change. We investigated how a community of butterflies responded to fine-scale changes in air temperature, and whether species-specific responses were predicted by ecological or morphological traits. Using data collected across a UK reserve network, we investigated the ability of 29 butterfly species to buffer thoracic temperature against changes in air temperature. First, we tested whether differences were attributable to taxonomic family, morphology or habitat association. We then investigated the relative importance of two buffering mechanisms: behavioural thermoregulation versus fine-scale microclimate selection. Finally, we tested whether species' responses to changing temperatures predicted their population trends from a UK-wide dataset. We found significant interspecific variation in buffering ability, which varied between families and increased with wing length. We also found interspecific differences in the relative importance of the two buffering mechanisms, with species relying on microclimate selection suffering larger population declines over the last 40 years than those that could alter their temperature behaviourally. Our results highlight the importance of understanding how different species respond to fine-scale temperature variation, and the value of taking microclimate into account in conservation management to ensure favourable conditions are maintained for temperature-sensitive species.