Assessing the insecticidal impact of rosemary essential oils on the saw-toothed grain beetle Oryzeaphilus surinamensis

Abstract

This work studied the fumigant toxicity of free and encapsulated rosemary (Rosmarinus officinalis) essential oils against adults of the saw-toothed grain beetle (Oryzeaphilus surinamensis) for three storage periods: 30, 45 and 60 days. Chitosan was used as encapsulation matrix. GC/MS analysis results showed that camphor and 1,8-cineole were the major components with respectively 18.04% and 39.67%. Mortality rates caused by the essential oils at 300 µL/L air after 10 days of storage were about 85.48%. The median lethal concentration (LC50) was 124.80 µL/ L air. Encapsulation efficacy was 25.8% and loading capacity was 1.9%. Encapsulated essential oils achieved an efficacy of 82%, 100% and 100% respectively after 30, 45 and 60 days of storage. Reference treatment with Phosphine revealed a toxicity of 100%, 96% and 71% after 30, 45 and 60 days of storage respectively. Results showed that encapsulated essential oils caused a very slight modification on semolina properties. Protein contents decreased at the end of the storage period less than 1% (from 13.61% after 30 days to 12.91% after 60 days of storage). Encapsulated essential oils might be considered as an alternative fumigant control way for semolina without deterioration of its quality during storage.