Development and Reproduction of a Japanese Strain of Ctenolepisma calvum (Ritter, 1910) at Room Temperature

SIMPLE SUMMARY: Ctenolepisma calvum, commonly known as the ghost silverfish, is an insect that lives in buildings, including museums, libraries, and archives. It is regarded as a pest of paper-based objects. Recently, C. calvum was discovered in several areas of Japan for the first time, and it may be a new threat to the conservation of collections that are of cultural and historical importance. Because the biological characteristics of this species in Japan are not well known, we observed their growth and reproduction. We found that eggs were laid from April to November, especially in early June, and eggs usually hatched within two months. The young insects grew through molting, and started laying eggs the next year. Females laid around 10 or more eggs at one time, and they were able to lay eggs once or more per year. Through this study, only females were found, and they were able to reproduce without male individuals. Further research on practical control methods for this species in museums and other facilities is required. ABSTRACT: Ctenolepisma calvum (Ritter, 1910) (Zygentoma: Lepismatidae) is a primitive wingless insect that causes damage to paper, and it is regarded as a pest of collections in museums, archives, and libraries. This species was recently discovered in Japan for the first time and may have already spread over large areas of Japan, but, currently, no information is available on the biological characteristics of C. calvum in Japan. In this study, we observed the processes of development and reproduction of C. calvum found in Japan at room temperature. Oviposition was observed from April to November, with a peak in early June. The average egg period was 56.9 days at average temperatures above 24.0 °C, and was 72.4 days at average temperatures below 24.0 °C. The 1st, 2nd, and 3rd instars lasted 4.7 days, 13.2 days, and 26.1 days on average, respectively, at average temperatures above 22.0 °C. Average instar periods were 23–28 days in 4th–7th instars and tended to increase in later instars. Instar periods also increased when the average temperature was 22.0 °C or lower. In individual rearing, the longest-living individual lived for approximately two years, up to the 15th instar. The head width grew at an approximate ratio of 1.1 per molt. First oviposition occurred at the 10th or 11th instar. Individually observed females oviposited once or twice a year, laying 6–16 eggs at one time, but females at least two years old laid 78.2 eggs per year on average in a mass-culture cage. Through this study, only females were found, and the mature females produced their progenies parthenogenetically.