Biological invasion by the cycad-specific scale pest Aulacaspis yasumatsui (Diaspididae) into Cycas revoluta (Cycadaceae) populations on Amami-Oshima and Okinawa-jima, Japan

Abstract

The islands of the Ryukyu archipelago in Japan are biologically diverse, supporting numerous plant and animal taxa found nowhere else. One of the most iconic plants is Cycas revoluta Thunb., the only cycad native to Japan. At this moment, the community of cycad researchers is concerned about the impacts caused by the recent invasion of the cycad aulacaspis scale (Aulacaspis yasumatsui Takagi) into the wild populations of C. revoluta in the islands of Amami-Oshima and Okinawa-jima. Within the last three decades, this cycad-specific scale has been inadvertently transported outside its native range in southeastern Asia and is known to cause high mortality on both wild and cultivated cycad species that are not evolutionarily and ecologically adapted to the effects of its infestation. Currently, neither the extent of the spread in Japan nor the attendant ecological impacts are well characterized; thus, several recommendations to mitigate the potential threat are proposed here. Monitoring the impact of the scale pest and evaluating the use of native predators as biological control organisms for A. yasumatsui are recommended. Considering the already known genetic diversity and spatial genetic structure of C. revoluta, we recommend establishing in situ and ex situ colonies to assure the conservation of its genetic composition in case of loss of populations.