Pivot burrowing of scarab beetle (Trypoxylus dichotomus) larva

Haruhiko Adachi,Satoshi Yagi,Makoto Seita,Makoto Ozawa,Shigeru Kondo

doi:10.1038/s41598-021-93915-0

Abstract

Many organisms live in the soil but only a little is known about their ecology especially movement style. Scarab beetle larvae do not have appendages to shovel soil and their trunk is thick compared to their body length. Hence, their movement through the soil is perplexing. Here, we established the observation and analysis system of larval movement and found that the last larval instars of Trypoxylus dichotomus burrow in two different ways, depending on the hardness of the soil. If the soil is soft, the larvae keep their body in a straight line and use longitudinal expansion and contraction; if the soil is hard, they flex and rotate their body. It is thought that the larvae adapt to diverse soil conditions using two different excavation methods. These results are important for understanding the soil ecology and pose a challenge to engineer of newer excavation technology.

Highlights

The soil is home to many organisms, and how they move through soil has been studied in several species by analyzing the shape of their burrows or/and using X-ray scanning technology[1,2,3,4,5,6,7,8,9,10,11]
Beetle larvae were placed on the soil surface to make sure they could burrow into the soil (Fig. 1a)
In order to observe the burrowing behavior, a two-dimensional (2D) observation tank (130 × 210 × ~ 20 mm) was constructed (Fig. 1b); we succeeded in observing the dynamics of the larvae under a 2D soil condition (Fig. 1c, Supplementary Movie 1)

Summary

Introduction

The soil is home to many organisms, and how they move through soil has been studied in several species (e.g., rats, lizards, snakes, nematodes, eels, spiders, ants, earthworms) by analyzing the shape of their burrows or/and using X-ray scanning technology[1,2,3,4,5,6,7,8,9,10,11]. Earthworms have attracted much attention as a research model because they can burrow through soil without appendages, and their dynamics have recently been elucidated via an observation system using transparent superabsorbent polymers[12]. Applications of these excavation techniques are being developed[13,14,15]. The larva of the scarab beetle (Trypoxylus dichotomus), which spend their life in the soil until adult emergence Their trunk is very thick compared to their body length; the transverse sectional diameter of an earthworm is approximately 2 mm[16], whereas that of the last instar larvae is ~ 20 mm. The beetle ecology in the soil has been reported in several studies[17,18], little is known about how the beetle larvae move

Methods

Findings

Conclusion