Studies on synanthropic silverfish fauna insecta zygentoma in selected areas of Kerala

Abstract

Silver fish are small, wingless, primitive cosmopolitan insects under the order Zygentoma. Of the, 677 species described under five families world-wide only 32 species from families Lepismatidae and Nicoletiidae have been reported from India. Many species are synanthropic and are considered pests but silverfish are generally undocumented or poorly documented especially from Asian countries. ZSI based researchers have made substantial contributions to the knowledge of Indian Zygentoma. Based on a recent checklist published in 2024, there is no authenticated reports of silverfish from Kerala. In this context the objectives of this study are to make a checklist of synanthropic silverfish species in selected areas of Kerala; to document the morphology of synanthropic silverfish species in the study area using conventional and modern taxonomic tools; to study the behaviour of selected silverfish species and to document and characterize the gut microbiome of selected silverfish species. Sample collection was repeatedly done from 69 sites during the period of December 2017 to March 2024, from seven randomly selected districts (Thrissur, Palakkad, Ernakulam, Kannur, Kottayam, Pathanamthitta, and Idukki) of Kerala, India. Silverfish habitus was imaged and measured using Leica S8AP0-MC180 HD, LABOMED Lx 300 compound microscope and SEM-EDAX. Identification was done following published taxonomic literature and consultation with experts. Sequencing of the COI of the species was done and compared with authenicated “DNA barcode” sequences from GenBank. Five species belonging to family Lepismatidae (Acrotelsa cf collaris, Thermobia smithi. sp. nov., Ctenolepisma rothschildi, Ctenolepisma longicaudatum and Ctenolepisma calvum-neotype) were documented. This included a species new to science and a neotype. The neotype redesignation led to the reassignment of a species in Europe (C. phantasma sp. nov.) as a species new to science. The behaviour of five synanthropic species of silverfish were observed in both natural and experimental set ups. Twenty unique behaviours were identified and classified into six broad categories Specialized behaviours such as “thanatosis” and “cannibalism” were documented. All the five species of silverfish showed similar types of behaviour and the major difference lay in the amount of time spent for each behaviour. Gut microbiome of four species of silverfish was documented for the first time. A total of 38 phyla belonging to 2 kingdoms - Bacteria (33) and Archaea (5) were isolated from the gut of the four silverfish species. A total of 684 species belonging to 450 genera, 272 families, 171 orders and 74 classes were documented. Succinivibrio dextrinosolvens, a cellulose-digesting bacterium, and many potential pathogenic bacteria were present in the gut microbiome of the silverfish. Recommendations on control of silverfish have been provided.