Abstract: 【Aim】 The horned-gall aphid, Schlechtendalia chinensis, is the major productive species of Chinese gallnuts. Understanding the biological characteristics and population dynamics of its overwintering nymphs under the condition of soilless moss in the field will provide a basis for further reducing the mortality of overwintering nymphs and increasing the yield of Chinese gallnuts. 【Methods】 The overwintering nymphs of S. chinensis were reared in the field on the host moss Plagiomnium maximoviczii which was planted on the non-woven fabrics. Mosses with S.chinensis at different developmental stages were collected regularly and brought back to the laboratory. The behavioral habits, morphological characteristics, population dynamics and instar distributions of S. chinensis nymphs during overwintering were investigated using a digital microscopic system. The thickness and coverage rate of P. maximoviczii duringtheoverwinteringperiodwere measured as well. 【Results】 Autumn migrants of S. chinensis reproduce ovoviviparously. The nymphs of S. chinensis excrete wax at the base of phyllidia of P. maximoviczii and wrap themselves individually to form wax balls where they feed and overwinter. Usually there is a single nymph in a wax ball. The body color of nymphs from the 1st instar to the 4th instar deepens gradually from light yellow to dark brown. The body length and width of nymphs increased with the nymphal instar, from 552.92±16.95 and 294.70±11.52 μm of the 1st instar nymphs to 1 205.25±10.75 and 593.15±7.66 μm of the 4th instar nymphs, respectively. During the overwintering period, the population density of nymphs dropped from 131 000 aphids/m² in mid-October to 10 500 aphids/m² in next March. The total mortality rate was as high as 91.98%. The developmental progress of overwintering nymphs was irregular and closely related to the changes of local temperature. The thickness and coverage rate of the moss layer increased gradually during overwintering of S. chinensis nymphs. 【Conclusion】 The body length and body width may be used as the main indicators for the identification of different instars of overwintering nymphs of S. chinensis. The total mortality rate of overwintering nymphs of S. chinensis in the field is very high, and the mortality rates during the early overwintering stage and the middle host-transferring stage are higher than those during the other stages.

Key words: Schlechtendalia chinensis, overwintering nymph, behavioral habit, morphology; population dynamics, instar distribution