The genus Eriosoma Leach, 1818 belonging to the subfamily Eriosomatinae (Hemiptera: Aphididae) includes 46 species in the world. The genus is mostly distributed in the Holarctic and Oriental regions. Most of the species in the genus form leaf-roll galls on Ulmus species. Until now, there are few studies about the genus on the morphological taxonomy in Korea. Up to date, seven species of the genus have been recorded from Korea. In the present study, a total of nine species of the genus is revised. Among them, two species, Eriosoma alabastrum Pashtshenko, 1988 and Eriosoma ulmi ulmi (Linnaeus, 1758), were discovered for the first time in Korea. We provide a key to the Korean species and full redescriptions in detail.

Woolly apple aphid, Eriosoma lanigerum, overwintered as adult or nymph stage on rootstocks, and crown- and root sucker in the soil. In an unsprayed apple orchard, the number of E. lanigerum colony started to increase from mid-April, showed the 1st peak between late June and early July, thereafter decreased followed by the 2nd peak in late July, and then again peaked in late September as the size in the 1st peak. In this orchard, the number of E. lanigerum colonies per tree did not exceed 3.5 colonies during the peak occurrence period, and was maintained around 2 colonies throughout seasons. In all seasons, parasitism of Aphelinus mali on E. lanigerum was much lower on root colonies than on aerial colonies that located on shoots and tree trunks above the ground. The parasitism of E. lanigerum was high in most orchards examined, showing parasitism of > 70% in maximum in most cases. In the laboratory bioassay for the mortality effects of several insecticides on E. lanigerum, fenitrothion, dichlorphos, machine oil, methidathion, thiacloprid, and imidacloprid showed 97.8, 96.8, 95.4, 91.5, 26.7, and 7.8% morality, respectively. Also, the adult emergence rates from A. mali mummies were 51.2, 72.6, 14.2, 3.5, 72.2, and 85.4% in the treatment of the above insecticides, respectively. Insecticides belong to neonicotinoid, which are newly developed to control aphids, showed low mortality against E. lanigerum. Fenitrothion and dichlorphos were effective on E. lanigerum control and had a low toxic to A. mali. Consequently, the insecticides should be useful in integrated pest management system for E. lanigerum in apple orchards.