Active sound production of scarab beetle larvae opens up new possibilities for species-specific pest monitoring in soils

Carolyn-Monika Görres,David Chesmore

doi:10.1038/s41598-019-46121-y

Carolyn-Monika Görres, David Chesmore

Open Access

https://doi.org/10.1038/s41598-019-46121-y

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Abstract

Root-feeding Scarabaeidae larvae can pose a serious threat to agricultural and forest ecosystems, but many details of larval ecology are still unknown. We developed an acoustic data analysis method based on active sound production by larvae (i.e. stridulations) for gaining new insights into larval ecology. In a laboratory study, third instar larvae of the Common Cockchafer (Melolontha melolontha) (n = 38) and the Forest Cockchafer (M. hippocastani) (n = 15) kept in soil-filled containers were acoustically monitored for 5 min each, resulting in the first known stridulation recordings for each species. Subsequent continuous monitoring of three M. hippocastani larvae over several hours showed that a single larva could stridulate more than 70 times per hour, and stridulation rates increased drastically with increasing larval abundance. The new fractal dimension-based data analysis method automatically detected audio sections with stridulations and provided a semi-quantitative estimate of stridulation activity. It is the first data analysis method specifically targeting Scarabaeidae larvae stridulations in soils, enabling for the first time non-invasive species-specific pest monitoring.

Highlights

The Melolonthinae, a subfamily of the scarab beetles (Scarabaeidae), comprises 29 tribes (Smith 2006) of which several pose a serious threat to agricultural and forest ecosystems all over the world (e.g. Keller and Zimmer 2005; Jackson & Klein 2006; Frew et al 2016)
The common stridulations of M. melolontha and M. hippocastani consisted of short bursts of sound (Fig. 2)
~1700 Hz, M. melolontha stridulations were of longer duration than the ones of M

Summary

Introduction

The Melolonthinae, a subfamily of the scarab beetles (Scarabaeidae), comprises 29 tribes (Smith 2006) of which several pose a serious threat to agricultural and forest ecosystems all over the world (e.g. Keller and Zimmer 2005; Jackson & Klein 2006; Frew et al 2016). While M. melolontha can be found in more open habitats (e.g. pastures, vegetable crops, orchards, vineyards), M. hippocastani mainly thrives in deciduous forests (Wagenhoff et al 2014; Sukovata et al 2015). These two species occur as pests in Austria, Czech Republic, France, Germany, Italy, Poland and Switzerland, but the available monitoring data is incomplete (Keller and Zimmer 2005), and Melolontha spp. outbreaks are expected to spread again after a decline in population sizes in the middle of the last century (Kahrer et al 2011). The reasons behind the recovery of Melolontha spp. populations are mainly unknown (Kahrer et al 2011), but are of serious concern as e.g. infested forest areas become more susceptible to droughts and secondary diseases, and forest regeneration can be hindered (Immler and Bussler 2008; Wagenhoff et al 2014; Sukovata et al 2015)

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Conclusion