Response of <i>Diaphorina citri</i> (Hemiptera: Liviidae) and its natural enemy <i>Harmonia axyridis</i> (Coleoptera: Coccinellidae) to plant odors

Abstract Diaphorina citri Kuwayama ( Hemiptera : Liviidae ) are one of the most common pests in orchards in China and in the United States. D. citri is a vector of Candidatus Liberibacter asiaticus, the bacteria that causes citrus greening or Huanglongbing. Huanglongbing has caused significant harm to the global citrus industry. Control of D. citri mainly relies on the application of pesticides, which can lead to environmental pollution, risks to human health, and does not prevent transmission of Huanglongbing. Determination of effective, eco-friendly, and complimentary prevention and control methods would be beneficial for D. citri management. Harmonia axyridis Pallas (Coleoptera: Coccinellidae) are a predator of D. citri. Identifying plants, which could be planted in citrus orchards, that have repellent effects on D. citri and are the preferred plants of H. axyridis is a promising ecological control method. A Y-tube olfactometer was used to study the behavioral responses of D. citri and H. axyridis to the odors of 40 plants. D. citri were significantly repelled by the odors of six plant species: Emilia sonchifolia DC. ex Wight ( Asteraceae ), Glebionis coronaria Tzvelev ( Asteraceae ), Artemisia selengensis Turcz. ex Besser ( Asteraceae ), Blumea balsamifera DC. ( Asteraceae ), Foeniculum vulgare Mill. (Apiaceae), and Agastache rugosa Kuntze (Lamiaceae). H. axyridis were significantly attracted to the odors of six plant species: Ulmus parvifolia Jacq. ( Ulmaceae ), Ligustrum sinense Lour. ( Oleaceae ), Koelreuteria paniculata Laxm. (Sapindaceae), Cycas revoluta Thunb. (Cycadaceae), Brassica pekinensis Hanelt ( Brassicaceae ), and Solanum melongena L. (Solanaceae). Plants both repellent to D. citri and attractive to H. axyridis have the potential for the development of eco-friendly control strategies for Huanglongbing.