Effectiveness of essential oils of Eucalyptus camaldulensis and Cymbopogon citratus in protecting stored rice against Sitophilus oryzae (Coleoptera: Curculionidae) and Sitotroga cerealella (Lepidoptera: Gelechiidae)

Abstract: The increase in sub-Saharan African rice production and the consequent resurgence of storage pests such as Sitophilus oryzae and Sitotroga cerealella require research measures to preserve the quality and quantity of stored crops. Chemical control methods are widely used on-farm for storage issue, but it is necessary to explore new measures to limit the risks of pesticides to producers and consumers’ health. The objective of this study was to develop alternative technologies based on the treatment of storage bags with the essential oils of Eucalyptus camaldulensis and Cymbopogon citratus to protect stored rice against these key pests. Two methods were used: impregnation of gunny bags and treatment of cotton bags. Gunny bags were soaked in oils diluted in alcohol at various concentrations (3%, 4% and 5%) corresponding to 2.34 ml, 3.12 ml and 3.9 ml/bag, respectively. Concerning cotton bags, they were treated either with a single oil (dose: 0.25 ml/bag) or with the two oils (half dose: 0.125 ml/bag). Twenty-four hours after application of the oils, 100 g of rice paddy were placed in each bag, and then each was artificially infested with 10 pairs of adults of S. oryzae and S. cerealella. After 90 days of storage, we assessed the populations of the two pest species and the damage inflicted on the stored rice. Impregnation of gunny bags and treatment of cotton bags with essential oils of C. citratus and E. camaldulensis effectively protected the stored rice against S. oryzae and S. cerealella. Moreover, the mixture of the two oils applied on cotton bags covered with plastic film, was the most effective treatment against these pests. Results obtained with these natural products are promising but before extending these technologies, it is necessary to investigate their effect on the quality of treated food and to ensure for consumer safety.