A holocyclic life cycle in a gall‐forming adelgid, Adelges japonicus (Homoptera: Adelgidae)

While the family Adelgidae (Homoptera) is typically holocyclic and periodically host‐alternating between a primary and secondary host, some anholocyclic species may persist exclusively on the primary or secondary host. In this study, we investigated the life cycle of Adelges japonicus , an anholocyclic species that utilizes either Picea jezoensis and Picea sitchensis (Pinaceae) as the primary hosts. Transfer experiments conducted in Hokkaido, the northern‐most island of Japan, revealed that A. japonicus also includes holocyclic forms that can migrate to the secondary host, Larix kaempferi . The holocyclic forms differed from anholocyclic forms in the date of gall dehiscence, oviposition preference of gallicolae and development of wax gland plates of gallicola adults. However, we treated these two forms as the same species because of a lack of information on their phylogenetic relationships and genetic isolation. Sequence of generations and developmental stages of each generation in the holocyclic forms were reported. Morphology of wax gland plates of first‐instar exulis was consistent with those of the subgenus Cholodkovskya , but different from those of the subgenus Adelges , to which A. japonicus has been assigned. Morphological comparison of gallicola adults suggests that the holocyclic forms were introduced to Hokkaido from central Japan.