Diatomaceous earth as insecticide: physiological and morphological evidence of its underlying mechanism

Abstract

BACKGROUND: Wheat grain containers or silos can be perfect habitats for insects, which generate large economic losses to grain production. Natural alternatives to synthetic insecticides had grown in popularity because of health, economic and ecological issues. Diatomaceous earth is a natural compound that has insecticide effect by enhancing insect´s dehydration with no toxicity on mammals including humans. The aim of this study is to confirm the effect of diatomaceous earth as insecticide for the wheat grain pest, the red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae) and demonstrate its underlying mechanisms as insecticide by open-flow respirometry, and Scanning Electron Microscopy.RESULTS: Survival bioassays of T. castaneum revealed a dose-dependent insecticide effect of diatomaceous earth. Gravimetric measurements showed that 2 days exposure to diatomaceous earth produce a significant increase of mass loss. Open-flow respirometry measurements showed an increase of total water emission rate on insects due to an increase of both, respiratory and cuticular water loss. Our study revealed that diatomaceous earth produces an increase of insect´s cuticle permeability, which is responsible of elevated cuticular water loss. Scanning Electron Microscopy images provided visual evidence of the lipid absorbent properties of diatomaceous earth particles, and showed a tendency to higher, although not significant, damaged area of the cuticle´s surface from diatomaceous earth treated insects compared to control ones.CONCLUSION: With state-of-the art techniques like open-flow respirometry and Scanning Electron Microscopy, we demonstrated the underlying mechanism of diatomaceous earth as insecticide and provided new cues for understanding cuticle’s properties and its ecological importance.