Abstract
In the northern distribution areas of the Asian citrus psyllid, Diaphorina citri in Japan, psyllid population densities in citrus groves were much lower than on Murraya paniculata hedges. We investigated the preference of D. citri adults for M. paniculata and Citrus unshiu to interpret such different occurrences. When D. citri adults were released into a screen house containing potted M. paniculata and C. unshiu, the number of adults on both plants increased until the 4th day after release. Thereafter, the mean densities remained relatively constant for 18 days on each plant species before the start of new adult emergence. On most M. paniculata trees, new shoots were always produced by late December, and adult densities increased after the increase of new shoots and declined one or two months after the peak density. New shoots of C. unshiu available for D. citri reproduction were produced only once on two trees, on which adult densities become abundant after the growth of new shoots and decreased gradually until late December. On the other four C. unshiu trees, adults migrated from other trees and their densities remained relatively constant. When D. citri adults were introduced into a preference test chamber containing buds and leaves of C. unshiu and M. paniculata, the adults were significantly more aggregated on the buds than on the leaves of both plants. No preference between C. unshiu and M. paniculata for either buds or leaves was detected. The present experimental results suggested that the difference in the population levels of D. citri on C. unshiu and M. paniculata in their northern distribution areas was not caused by the preference of the insect, but may be due to continuous production of new shoots and dense planting of M. paniculata hedges favoring the reproduction and survival of D. citri during the typhoon season and winter.
