Invasive and Quarantine Risks of Cacopsylla chinensis (Hemiptera: Psyllidae) in East Asia: Hybridization or Gene Flow Between Differentiated Lineages.

Pear psyllids are major pests and the causal agents of pear decline disease in orchards. In the past two decades, their outbreaks have raised issues pertaining to invasions and taxonomic identification of the dimorphic Cacopsylla chinensis (Yang and Li) in East Asia. The present study elucidated, as an aid to quarantine management, the invasive origins, differentiation history, and putative gene flow and hybridization between C. chinensis and its sibling species Cacopsylla jukyungi (Kwon). Analyses revealed that the ancestors of C. jukyungi might have diverged from C. chinensis approximately 3.5 million yr ago (Mya) and that differentiation between C. chinensis lineages I and II probably occurred 1.5 Mya. The known overlapping distribution of C. chinensis and C. jukyungi in northeastern China and the two C. chinensis lineages in the Bohai Rim region and Taiwan could be attributed to recent population expansion after the Last Glacial Maximum and/or anthropogenic activities. Analyses of the nuclear gene demonstrated that frequent gene flow between the two C. chinensis lineages and the paraphyletic relationship between C. chinensis and C. jukyungi might be caused by incomplete lineage sorting or hybridization events. On the basis of the current distribution, it is evident that C. jukyungi is not present in middle-southern China, whereas C. chinensis is not distributed in Japan and Korea. Preventing new invasions of Cacopsylla psyllids among geographic regions through the transportation of pear scions is thus pivotal in East Asia, particularly for the possible genetic exchanges among differentiated lineages after secondary invasion events.