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

Abstract: The decline in semi-natural habitat is posing a threat to several grassland insect species, including the silver-studded blue butterfly, Plebejus subsolanus ssp. iburiensis, which is listed as a “nationally rare species of wild fauna in Japan”. We investigated the effects of mowing on the larvae and adults stages of P. subsolanus in the same population in a conservation area, aiming to identify effective habitat management for this species and all coexisting butterflies. We surveyed the number P. subsolanus larvae and adults, host plant characteristics, butterfly abundance, species richness, and flowering plant metrics in both mowed and unmowed areas. Larvae only appeared in the mowed area, and the cover and height of host plant were significantly higher in the mowed area. P. subsolanus adults and butterfly abundance were higher in the mowed area. No statistical differences were observed in the butterfly species richness, inflorescences and species numbers of flowering plants, or the vegetation height between the mowed and unmowed areas. Mowing has a positive effect on P. subsolanus larvae and adults, while it has a limited effect on reducing vegetation height. The negative correlation with butterfly species richness, flowering plant species, and inflorescences underscores the need to maintain optimal vegetation height in these areas, to control excessive vegetation growth. Implications for insect conservation: Our results show that mowing conducted concurrently with the pupal stage and egg stage could be effective in the conservation management of butterfly and floral communities, including P. subsolanus and its host plants.