Volatile-Oil-Based Strategy to Combat the Insect Vector for Most Destructive Citrus Disease in World

A new strategy for combating the vector of the bacterium that causes “citrus greening disease” (huanglongbing or HLB) considered the most destructive citrus disease in the world and present in 17% of orange trees in São Paulo State, Brazil, may be developed from the discovery that three citrus plants produce an essential oil that repels the insect. Brazilian researchers, affiliated with the Federal University of São Carlos (UFSCar) and working under the aegis of the National Institute of Science & Technology for Biorational Control of Insect Pests (INCT-CBIP), funded by the National Council for Scientific & Technological Development (CNPq) and by FAPESP, analyzed the chemical composition of the essential oils produced by 22 species of the genus Citrus, including oranges, limes, and tangerines. Their purpose was to understand the effects of these substances on organisms-- such as Diaphorina citri, the Asian citrus psylli--that interact with the plants. D. citri transmits Candidatus liberibacter spp, including the bacterium that causes HLB. The analysis was performed as part of the Thematic Project "Integrated studies for leaf cutting control", also supported by FAPESP. D. citri is only 3 mm long. It sucks sap from terminal shoots, but does not cause significant direct damage. What destroys the citrus plant is the bacterium transmitted by the insect's eggs--a single female D. citri lays as many as 800 eggs. The researchers discovered that the insect prefers to lay eggs on certain citrus species rather than others. Two in particular are unattractive to D. citri, namely Citrus reticulata, known as the Murcott mandarin, and the Swingle citrumelo, a hybrid of C. paradisi grapefruit with Poncirus trifoliata, the trifoliate orange.
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