Ladybird beetle trails affect population growth of the brown citrus aphid, Toxoptera citricida

The brown citrus aphid, Toxoptera citricida is a pest of citrus because it efficiently transmits severe strains of Citrus tristeza virus (CTV). Little is known about the behavioral interactions of T. citricida with trail chemicals of its ladybeetle predators, Hippodamia convergens. We investigated the host settling behavior and population growth rate of T. citricida in response to trail chemicals deposited by the ladybeetle, Hippodamia convergens. In addition, the repellency of the ladybeetle to their conspecifics trail was evaluated in laboratory olfactometer assays. We found that host settling behavior of T. citricida on plant surfaces was not affected 5 or 24 hr after ladybeetle trails were deposited as compared with untreated controls. However, the population growth rate of T. citricida was significantly reduced on plants containing ladybeetle trails as compared with control plant surfaces 3, 7, and 10 days after treatment. Similarly, the population growth rate of T. citricida was reduced on plant surfaces treated with H. convergens trail extract 10 and 15 day after treatment as compared with on control seedlings. Behavioral assays revealed H. convergens was not repelled by the trail extracts of conspecifics. We discuss potential practical application of ladybird trails for managing T. citricida without negative effects on ladybird beetle behavioral response.