Nipponaphis loochooensis Sorin, 1996 and N. machilicola (Shinji, 1941) form fig-shaped or globular galls on Distylium racemosum in southern Japan. Nipponaphis machilicola migrates to the lauraceous evergreen Machilus thunbergii. Nipponaphis loochooensis has also been supposed to migrate to M. thunbergii, but its secondary-host generation has not been found in the field to date. Through sampling Nipponaphis aphids from trees of M. japonica in addition to M. thunbergii, and sequencing their mitochondrial DNA, we found that the two species form colonies on twigs of both Machilus species, and that the two at times colonize on the same trees and even form mixed colonies. Only N. loochooensis forms colonies on leaves of M. japonica, but neither species colonizes on leaves of M. thunbergii. The secondary-host generations of the two species could be clearly discriminated from each other, based on morphology. It was confirmed by examining the type specimens of Nipponaphis amamiana Takahashi, that the name is a junior synonym of N. machilicola.
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