Effect of mowing on population maintenance of the endangered silver-studded blue butterfly, Plebejus subsolanus iburiensis (Lepidoptera: Lycaenidae), throughout its life cycle

Abstract

Introduction: The decline in semi-natural grasslands is posing a threat to several grassland insect species, including the silver-studded blue butterfly, Plebejus subsolanus ssp. iburiensis, which is nationally rare species of wild fauna in Japan. Aims: This study aimed to investigate the impact of mowing on larval and adult populations of P. subsolanus in a conservation area and to identify suitable habitat management methods for this species and other butterflies. We surveyed the number of larvae and adults of P. subsolanus, other butterfly species, and the height, cover, and number of inflorescences of the host plant (Vicia unijuga), in both mowed and unmowed areas. Results: Larvae only appeared in the mowed area, and the cover and height of host plant were markedly higher in the mowed area. Furthermore, the number of adult P. subsolanus was substantially higher in the mowed areas. However, no statistical differences were observed in the number of other butterfly species, species richness, inflorescences or number of flowering plants between the mowed and unmowed areas. Discussion: The mowed area is an important habitat for both larvae and adults of P. subsolanus. Although there were no differences in the number of other butterfly species and flowering plants between the mowed and unmowed areas, the vegetation height was negatively correlated with these variables. Implications for insect conservation: Our results show that the creation of areas with reduced vegetation height could be effective in the conservation management of butterfly and floral communities, including P. subsolanus and its host plants.