Further study of the multivoltine strain of the snout butterfly Libythea lepita (Nymphalidae, Libytheinae) inhabiting Honshu, the main island of Japan

Abstract

Although the snout butterfly, Libythea lepita, is commonly thought of as univoltine or at most bivoltine in regions further north than the Amami Islands in Kagoshima Prefecture, Japan, we previously found a multivoltine strain of this butterfly distributed in Fukui Prefecture. To confirm the reproducibility of the rearing results in 2018, we revisited the same site on May 27, 2019, where we found L. lepita individuals at various developmental stages, i.e., many fourth to fifth instar larvae (group A), old adults with damaged wings (group B), adults with slightly defaced wings (group C), eggs (group D), and a small number of fresh females (group E) laying eggs on Japanese hackberry (Celtis sinensis). The results of rearing these individuals in an outdoor cage showed that only group C produced 4 generations within a year, indicating that at least group C consisted of individuals with a multivoltine trait. In the following year (2020), 3 generations were obtained from the offspring of group C that had hibernated. In addition, another multivoltine strain of L. lepita newly found in the spring of 2023 in Hiroshima Prefecture located in western Japan also had 4 broods in the outdoor cage. This strongly suggests that univoltine and multivoltine populations of L. lepita may coexist in most habitats of the butterfly. Photoperiodic experiments designed to examine the effect of day length on female ovarian development showed that while long-day treatment in adulthood tended to promote ovarian development, day length during the larval stage had no decisive effect on the outcome. The results also suggested the presence of an obligatory diapausing (univoltine) strain that is insensitive to photoperiod.