# A Beetle In Vitro: Establishment of a Short-Term Cell Culture from the Pest Popillia japonica

## TL;DR

Scientists created the first short-term cell culture from Japanese beetle larvae, enabling lab studies to better understand and control this invasive pest.

## Contribution

The first successful establishment of a short-term cell culture from Japanese beetle larvae for in vitro biological studies.

## Key findings

- Cells from Japanese beetle larvae fat bodies were cultured and maintained in the lab for multiple cycles.
- Transcriptomic analysis showed moderate gene expression changes related to stress and iron homeostasis in cultured cells.
- The cell culture contains trophocyte-like cells and lipid droplets, typical of insect fat bodies.

## Abstract

The Japanese beetle is an invasive insect that causes serious damage to agriculture and natural ecosystems. Until now, no means of studying its biology in the lab have been available using living cells, limiting progress in understanding this pest and controlling its invasion. In this study, we developed the first cell culture from Japanese beetle larvae using fat bodies, a tissue important for growth and energy storage. These cells were successfully grown and maintained in the laboratory over multiple cycles, showing stable appearance and healthy structure for a limited period. This new cell culture represents a short-term and accessible in vitro system for studying the beetle’s biology in controlled conditions. Although we failed to establish an immortalized cell line, they provide a useful model for investigating cytological and physiological responses to treatments, leading to understanding how the beetles can be affected by control strategies. This work lays the groundwork for future discoveries that could support better, more targeted approaches to managing this harmful species.

The Japanese beetle (Popillia japonica Newman) is a highly invasive, polyphagous scarab causing significant agricultural and ecological damage across invaded regions. While molecular studies are gaining traction, the unavailability of P. japonica cell lines has constrained in vitro investigations. To overcome these limitations and provide a platform for controlled biological investigation, we developed the first cell culture derived from P. japonica larvae. Fat bodies from field-collected third-instar larvae were dissected and cultured. Cells initially formed floating spheroids before transitioning to adherent monolayers. Cultures remained stable over several splits, whereas a marked reduction in cell number was observed at the eighth split due to the onset of contamination. Fluorescence microscopy confirmed nuclear integrity, while transmission electron microscopy at split 5 revealed cytoplasmic features consistent with insect fat body cells, including lipid droplets. The cell culture predominantly contained trophocyte-like cells, consistent with the known cellular composition of insect fat bodies. Transcriptomic analyses comparing fresh fat bodies and cultured cells revealed moderate transcriptional divergence, with limited upregulation of genes associated with iron homeostasis and stress response, consistent with adaptive responses to in vitro conditions. While not immortalized, this cell culture offers a short-term model for studying P. japonica physiology, toxicology, host–pathogen interactions, and potential gene-targeting strategies under controlled conditions. This work represents a first step toward enabling molecular and cellular research in this economically important pest species.