Inspection of frass ejection could decrease the risk of white-spotted longicorn beetle Anoplophora malasiaca (Coleoptera: Cerambycidae) infestation of Japanese pine bonsais to negligible levels

To evaluate the infection risk of Anoplophora malasiaca (Thomson) (Coleoptera: Cerambycidae) in two species of Japanese pine bonsais (Japanese black pine and Japanese white pine), feeding and oviposition preferences of female A. malasiaca to pine bonsai and mandarin orange were examined. A female was released into a net cage together with a pair of one pine bonsai and one mandarin orange. All mandarin oranges used in preference tests were damaged by feeding and deep biting scars from females, and larval frass ejection from the trunk was found in some mandarin oranges within 4 months of observation. However, these scars were found on only a few pine bonsais, and frass ejection was not found in any pine bonsais. No A. malasiaca larvae were detected in these pine bonsais. Therefore, frass ejection from trunks might be indicative of the presence of larvae. In field surveys at bonsai nurseries, no A. malasiaca adults were found on the pine bonsais and no pine bonsais exhibited frass ejection. Statistical analyses of these results suggested that the risk of A. malasiaca infestation in pine bonsais could be ruled out as a negligible level by confirming an absence from the trunk of frass ejection.