Host plant selection and differential survival on two Aristolochia L. species in an insular population of Zerynthia cassandra

Abstract

Understanding host plant preference and the relative quality of resource provided by cooccurring host plants is a key step to predict butterfly species abundance and responses to environmental changes, and, consequently, to plan management measures. Zerynthia cassandra is an Italian endemic species strongly dependent on the availability of its host plants, Aristolochia rotunda and A. lutea. The insular population occurring on Elba island (Tuscan Archipelago) is highly threatened, because of limited host plant distribution, small population size and apparent lack of gene flow with the mainland. In 2017, we carried out field surveys and rearing experiments to i) identify the characteristics of the host plants (vegetative status) and the site characteristics (aspect, irradiation, distance from other patches) correlated with the number of eggs occurring on individual plants, ii) compare larval growth, food-conversions rate and larval and adult survivorship on the two host plants species. Egg occurrence depends on patch irradiation, the number of leaves and flowers occurring on individual plants and the occurrence of nearby patches. These findings allowed to identify the optimal Aristolochia patch features for egg laying and development.Laboratory rearing success was higher than 50% and although plant species did not show a significant effect on oviposition, we found that larval and adult survival was higher on A. rotunda. Our results suggest habitat management aimed at increasing resource availability for Z. cassandra and possible ex-situ conservation actions aimed at recovering the population in case of potential catastrophic events.

A sunny spot: habitat management through vegetation cuts increases oviposition in abandoned fields in an endemic Mediterranean butterfly

“…Zerynthia cassandra is strictly dependent on its Aristolochia host plants, such as A. rotunda and A. lutea , for oviposition and larval growth (Vovlas et al ., 2014; Camerini et al ., 2018; Ghesini et al ., 2018; Cini et al ., 2019), which are herbaceous plants with an underground persistent apparatus and aerial annual stems. Aristolochia rotunda and A. lutea show differences in the micro‐habitat preferences, with the former being more common in hill‐mountain areas (Nardi, 1984).…”

“…Aristolochia rotunda and A. lutea show differences in the micro‐habitat preferences, with the former being more common in hill‐mountain areas (Nardi, 1984). The two species are present on Elba island where they are both linked to humid micro‐habitats where they can coexist (Cini et al ., 2019). Previous findings suggest that plant species ( A. rotunda vs .…”

“…Previous findings suggest that plant species ( A. rotunda vs . A. lutea ) did not influence oviposition but has an effect on larval and adult survivorship, with larvae having higher survivorship and adults having a longer lifespan when fed on A. rotunda compared to A. lutea (Cini et al ., 2019). Adults feed on several herbaceous nectar sources (Ghesini et al ., 2018 and personal observation).…”

“…It is a monophagous species (sensu Stephens et al ., 2008) which feeds on few plants of the Aristolochia genus L. (Fig. 1b), that represent the crucial resource determining population size and survival (Vovlas et al ., 2014; Ghesini et al ., 2018; Cini et al ., 2019). Z. cassandra is included in the Appendix IV of the Habitats Directive and in the Appendix II of the Bern Convention and shows two insular populations also recognised as distinct subspecies (Bollino & Racheli, 2012): a very large population on Sicily island and a much more reduced population on Elba island.…”

“…and Aristolochia rotunda L. occur on the island; Nardi, 1984). Indeed, previous studies agreed that Z. cassandra prefers to lay eggs on Aristolochia shoots exposed to a high level of irradiation (Vovlas et al ., 2014; Ghesini et al ., 2018; Cini et al ., 2019). Moreover, shrub growth can reduce larval fitness for several reasons.…”