The orange wheat blossom midge (OWBM),Sitodiplosis mosellana (Gehin), is one of the most important pests of winter wheat in North China. It often feeds on developing wheat kernels and can cause a serious yield loss of this cereal. There were 2.4 million hectares with OWBM occurrence in 2013 in China. On the other hand, from the 1950s to the present time, the northern boundary of the OWBM occurrence area has shifted towards the pole by about four degrees of latitude (440 km) in North China. The northern area of North China, including Hebei, Beijing, Tianjin and northwestern Shandong, has become a novel occurrence region. This investigation was carried out on bagged ears of flag leaf, ear emergent and flowering stages of the winter wheat cultivar, Luomai 24, protected from the OWBM in fields in 2012 at Jiaozhaivillage, Luolong district, Luoyang city, Henan. The OWBM adults were monitored in April and May with yellow sticky traps, and the adult period of OWBM was found to overlap with the ear emergent and flowering stages of the cultivar. There were no damaged bagged ears in the flag leaf stage. The yield losses in bagged ears from 1/4 to 3/4 ear emergence were significantly less than in the fully ear emergent stage, but there were no significant differences between bagged early and late flowering stages. However, the yield loss in bagged flowering ears (average 10.79%) was significantly higher than in the bagged ear emergent stage (average 3.48%).The result revealed that emerging ears are susceptible to OWBM infestation. The damage level was evaluated in terms of synchronization of ear emergence stages of winter wheat cultivars with occurrence periods of OWBM adults in the 2012 and 2013 crop growing seasons. More than 400 susceptible cultivars were evaluated. Because of a 2℃ lower temperature on 19 April 2013, the adult period ran from 4 May to 13 May that year. Synchronization was calculated using the niche overlap formula (Geange et al 2011). In the 2012 growing season, the maximum synchronization value for 23 cultivars was 0.628 when the ear emergent stage ran from 22 April to 28 April, and the average yield loss was 78.1%. The minimum synchronization value was 0.307 for three cultivars when the ear emergent stage ran from 28 April to 2 May, and the average yield loss was 11.7%. In the 2013 growing season, the maximum synchronization value for three cultivars was 0.783 when the ear emergent stage ran from 4 May to 11 May, and the average yield loss was 2.41%. The minimum value for 11 cultivars was 0.062 when the ear emergent stage ran from 15 April to 25 April, and the average yield loss was 0.04%. The results obtained indicate that higher synchronization values led to more serious yield losses and there was a significant relationship between them. The yield losses of wheat cultivars showed a significant positive correlation with the total number of OWBM adults during the ear emergent stage. This conclusion indicates that the control strategy should be aimed at chemical protection of the ear emergent stage in China until resistant wheat cultivars are planted, because the infestive OWBM occurrence period is in the ear emergent stages of winter wheat, and not the flowering stage. At the same time, the result may help to explain why the OWBM occurrence area has shifted towards the pole because the average winter and spring temperature has risen by 1.5℃ since the 1950s in the northern area of North China, and there might now be an synchronous or matched status between wheat ear emergent stage and OWBM adults in the northern area of North China.