Clear-cuts are temporary habitats, not matrix, for endangered grassland burnet moths (Zygaena spp.)

Burnet moths (Zygaena spp.) are day-flying Lepidoptera considered indicative of species-rich grasslands. In the present study, our aim was to clarify whether clear-cuts are habitat, supporting habitat or matrix for three species of Zygaena. We did so by sampling these species with sex pheromones on 48 clear-cuts, varying in amount of host and nectar plants, in southern Sweden. To compare the efficiency of such sampling, we also conducted transect walks on these clearcuts. Overall, host-plants on clear-cuts best explained the abundance of Zygaena spp. recorded, better than nectar-plants or connectivity with nearby grasslands. These results indicate that clear-cuts with an abundance of host plants are used as a fully functional habitat, and not a supporting habitat in the sense of only providing nectar. There is no support in these results for considering clear-cuts as an inert matrix. With about half the work-effort, pheromone traps recorded 100 times more Zygaena spp. as transect walks. The poor correspondence between observations during transects walks and pheromone trap catches suggest Zygaena spp. being difficult to monitor by transect walks. In contrast to grasslands, clear-cuts are short-term in nature requiring repeated recolonization, indicating the importance of permanent grasslands. However, clear-cuts are important temporary insect habitats due to their great acreage, and suitable management can increase the time they remain a habitat

Revealing hidden species distribution with pheromones: the case of Synanthedon vespiformis (Lepidoptera: Sesiidae) in Sweden

Synanthedon vespiformis L. (Lepidoptera: Sesiidae) is considered a rare insect in Sweden, discovered in 1860, with only a few observations recorded until a sex pheromone attractant became available recently. This study details a national survey conducted using pheromones as a sampling method for this species. Through pheromone trapping we captured 439 specimens in Southern Sweden at 77 sites, almost tripling the number of previously reported records for this species. The results suggest that S. vespiformis is truly a rare species with a genuinely scattered distribution, but can be locally abundant. Habitat analyses were conducted in order to test the relationship between habitat quality and the number of individuals caught. In Sweden, S. vespiformis is thought to be associated with oak hosts, but our attempts to predict its occurrence by the abundance of oaks yielded no significant relationships. We therefore suggest that sampling bias and limited knowledge on distribution may have led to the assumption that this species is primarily reliant on oaks in the northern part of its range, whereas it may in fact be polyphagous, similar to S. vespiformis found as an agricultural pest in Central and Southern Europe. We conclude that pheromones can massively enhance sampling potential for this and other rare lepidopteran species. Large-scale pheromone-based surveys provide a snapshot of true presences and absences across a considerable part of a species national distribution range, and thus for the first time provide a viable means of systematically assessing changes in distribution over time with high spatiotemporal resolution

Rewiring of interactions in a changing environment: nettle-feeding butterflies and their parasitoids

Climate and land use change can alter the incidence and strength of biotic interactions, with important effects on the distribution, abundance and function of species. To assess the importance of these effects and their dynamics, studies quantifying how biotic interactions change in space and time are needed. We studied interactions between nettle-feeding butterflies and their shared natural enemies (parasitoids) locally and across 500 km latitudinal gradient in Sweden. We also examined the potential impact of the range-expansion of the butterfly Araschnia levana on resident butterflies via shared parasitoids, by studying how parasitism in resident butterflies covaries with the presence or absence of the newly-established species. We collected 6777 larvae of four nettle-feeding butterfly species (Aglais urticae, Aglais io, Ar. levana and Vanessa atalanta), over two years, at 19 sites distributed along the gradient. We documented the parasitoid complex for each butterfly species and measured their overlap, and analysed how parasitism rates were affected by butterfly species assemblage, variations in abundance, time, and the arrival of Ar. levana. Parasitoids caused high mortality, with substantial overlap in the complex of parasitoids associated with the four host butterflies. Levels of parasitism differed significantly among butterflies and were influenced by the local butterfly species assemblage. Our results also suggest that parasitism in resident butterflies is elevated at sites where Ar. levana has been established for a longer period. In our study system, variations in butterfly species assemblages were associated in a predictable way with substantial variations in rates of parasitism. This relationship is likely to affect the dynamics of the butterfly host species, and potentially cascade to the larger number of species with which they interact. These results highlight the importance of indirect interactions and their potential to reorganise ecological communities, especially in the context of shifts in species distributions in a warmer world.</p

Integrating national Red Lists for prioritising conservation actions for European butterflies

Red Lists are very valuable tools in nature conservation at global, continental and (sub-) national scales. In an attempt to prioritise conservation actions for European butterflies, we compiled a database with species lists and Red Lists of all European countries, including the Macaronesian archipelagos (Azores, Madeira and Canary Islands). In total, we compiled national species lists for 42 countries and national Red Lists for 34 of these. The most species-rich countries in Europe are Italy, Russia and France with more than 250 species each. Endemic species are mainly found on the Macaronesian archipelagos and on the Mediterranean islands. By attributing numerical values proportionate to the threat statuses in the different national Red List categories, we calculated a mean Red List value for every country (cRLV) and a weighted Red List value for every species (wsRLV) using the square root of the country's area as a weighting factor. Countries with the highest cRLV were industrialised (NW) European countries such as the Netherlands, Belgium, the Czech Republic and Denmark, whereas large Mediterranean countries such as Spain and Italy had the lowest cRLV. Species for which a Red List assessment was available in at least two European countries and with a relatively high wsRLV (50) are Colias myrmidone, Pseudochazara orestes, Tomares nogelii, Colias chrysotheme and Coenonympha oedippus. We compared these wsRLVs with the species statuses on the European Red List to identify possible mismatches. We discuss how this complementary method can help to prioritise butterfly conservation on the continental and/or the (sub-)national scale