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

Root-feeding Scarabaeidae larvaecan pose a serious threat to agricultural and forest ecosystems, but many details of larval ecology are still unknown. We developed an acoustic data analysismethod based on active sound production by larvae(i.e. stridulations) for gaining new insights into larval ecology. In a laboratory study, third instar larvaeof 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 stridulationrecordings for each species. Subsequent continuous monitoring of three M. hippocastani larvaeover several hours showed that a single larvacould stridulatemore than 70 times per hour, and stridulationrates increased drastically with increasing larval abundance. The new fractal dimension-based data analysismethod automatically detected audio sections with stridulationsand provided a semi-quantitative estimate of stridulationactivity. It is the first data analysismethod specifically targeting Scarabaeidae larvae stridulationsin soils, enabling for the first time non- invasive species-specific pest monitoring.