Exploring Sitophilus (Coleoptera; Curculionidae) behaviour using a four-arm olfactometer: A step towards sustainable pest management in rice storage

Infestations by Sitophilus spp. (Coleoptera; Curculionidae) grain weevils pose a significant threat to rice storage1, resulting in significant losses. Preventing such infestations is crucial due to rice's importance in diets. Chemical solutions, while common, raise concerns about environmental impact and public health2 necessitating alternative approaches.

This study focuses on understanding and managing Sitophilus behaviour using compounds with possible repellent/deterrent behaviour. Experiments utilized a four-arm olfactometer with four airflow inlets, to assess insect responses to stimuli under controlled conditions. Insects' behaviour towards rice flour on a cotton disk was contrasting with the cotton disk alone. When testing compounds, we utilized two olfactometer arms: one with the attractive compound and the other with normal airflow. The olfactometer central chamber was partitioned into three regions, and insect activity was observed over 10 minutes, annotating the time spent in each region (far, medium/central, and near the odor source). The chamber with the odor source was periodically rotated, and assays were performed under red light at 25°C and 30% RH. For each compound, a total of 15 replicate insects were individually tested.

Results showed that the presence of the cotton disk did not significantly influence insect behaviour (p-value=0.38571). However, insects preferred the rice flour region, spending significantly more time near the attractive flow (p-value=0.001173).

These findings suggest that the olfactometer device did not affect insect behaviour, and future studies will explore the repellent properties of essential oils' primary compounds, including S-(-)-limonene, eugenol, eucalyptol, L-menthol, and thymol (natural and food grade). Essential oils, rich in volatile compounds, offer promising alternatives for preventing rice infestations, as they boast antifungal and repellent qualities, along with insecticidal properties against stored-product pests3. Building upon the encouraging outcomes of this study, we seek to further investigate novel solutions for controlling weevil infestations in stored rice.