The overwintering generation of the grass webworm has once again produced a peak in adult emergence, and there is a clear trend of a resurgence in the first-generation larvae.

Release Date:

2020-06-30

Following the emergence of peak adult moth flights of the overwintering generation in Inner Mongolia, Shanxi, Hebei, and other regions in late May and early June, recent monitoring has revealed even higher moth peaks at light traps across multiple locations in Inner Mongolia, Shanxi, Hebei, and Liaoning, accompanied by a sharp increase in field populations. In some fields, eggs and newly hatched larvae have already been observed. At present, the area affected by overwintering adults nationwide stands at 5.2 million mu, while the area infested with first-generation eggs and larvae totals 260,000 mu.
　　I. Large moth populations under lights in Inner Mongolia, Shanxi, Hebei, and Liaoning provinces
　　Since mid-June, nine leagues and cities in Inner Mongolia—Bayannur, Ordos, Baotou, Ulanqab, Hohhot, Xilingol, Chifeng, Hinggan League, and Hulunbuir—have recorded peak moth catches at light traps. At a total of 14 monitoring sites, high-altitude light traps have registered peaks ranging from tens of thousands to over several hundred thousand moths, with catch levels unprecedented in recent history. In Wulate Middle Banner of Bayannur City, the average daily moth catch at high-altitude lights from June 18 to 20 was 650,000, peaking at 930,000 on June 19; ovarian development stages 1–2 and 3–4 accounted for 70% and 30%, respectively. In Wulate Rear Banner, the high-altitude light trap on June 19 captured 260,000 moths, with stages 2 and 3 representing 70% and 30%, respectively. In Linhe District, the high-altitude and forecasting lights on June 18 each attracted more than 20,000 moths. In Dalad Banner of Ordos City, the average daily catch at high-altitude lights from June 18 to 20 was 67,000. In Tumed Right Banner of Baotou City, both high-altitude and forecasting lights recorded daily catches exceeding 10,000 during June 18–19, with ovarian development predominantly at stages 3–4. In Taibusi Banner of Xilingol League and Balin Left Banner of Chifeng City, cumulative catches from June 16 to 20 totaled 11,000 and 10,000, respectively. In Kezuoyouqian Banner of Hinggan League, the average daily catch at high-altitude lights from May 29 to June 21 was 38,000, with peaks of 328,000 on June 12, 221,000 on June 20, and 163,000 on June 22.
　　In Yungang District, Datong City, Shanxi Province, high-altitude light traps recorded a cumulative catch of over 120,000 moths from June 15 to 22, with peak activity occurring between June 19 and 22. Ovarian development stages 1–2 and 3–4 accounted for 55% and 45%, respectively. In Dai County, since mid-June, daily moth catches at high-altitude light traps have exceeded 1,000 individuals, reaching a peak of 7,000 on June 19.
　　In the Zhangjiakou–Chengde region of Hebei Province, moth catches surged from June 15 to 21. In Weichang County, black-light traps accumulated 36,765 moths, with daily catches exceeding 10,000 on both the 17th and 18th. In Wanquan District of Zhangjiakou City, monitoring lamps recorded a cumulative total of 6,699 moths, with average daily catches surpassing 1,000 from the 19th to the 21st. In Kangbao County, high-altitude lights captured 1,392 moths, while monitoring lamps accumulated 721 moths. In Yanqing District of Beijing, high-altitude lights attracted 9,765 moths between June 15 and 22.
　　In western Liaoning, a peak in moth activity occurred from late June to early July. Specifically, in Jianping County, the high-altitude light trap recorded a cumulative catch of 17,000 moths from June 16 to 22, while the monitoring lamp captured 2,000 moths; ovary development was predominantly at stage 3. In Lingyuan City, the high-altitude light trap accumulated 3,000 moths on June 15–16. In Zhangwu County, the high-altitude light trap attracted 712 moths from June 16 to 19.
　　From June 11 to 24 in Ningxia, the high-altitude light trap in Pingluo County recorded a cumulative catch of 413 moths, while the monitoring lamp captured 18 moths. In Huirong District, the monitoring lamp registered a cumulative catch of 11 moths.
　　Adults were first observed in Heilongjiang and Jilin in late May, 2 to 7 days later than the long-term average. Moth populations remained low across all regions; with the exception of the Beilin District and Zhenlai County, which recorded cumulative trap catches of 174 and 128 moths, respectively, all other localities reported cumulative totals below 50 moths per light trap.
　　II. In Inner Mongolia and other regions, moth populations are high and the affected area is extensive.
　　In Inner Mongolia, the overwintering generation of adult moths was observed across 5.07 million mu of farmland, with 1.91 million mu in Baotou City and 600,000 to 750,000 mu each in Ordos City, Hohhot City, Bayannur City, and Hinggan League; other leagues and cities reported less than 300,000 mu. The peak moth population in fields occurred from June 18 to 20, with an average of 500 to 2,000 moths per hundred steps. In areas adjacent to farmland—particularly on grassy fallows or in localized patches with abundant weeds—the density reached 5,000 to 10,000 moths per hundred steps.
　　In Yunzhou District, Datong City, Shanxi Province, the area infested by adult moths totals 2,000 mu, with a density of 3,000 to 5,000 larvae per 100 steps in alfalfa fields.
　　In Wanquan District, Kangbao County, Weichang County, Fengning County, and other areas of Hebei Province, the area infested with adult moths totaled 109,000 mu, including 43,000 mu in farmland, 63,000 mu on grasslands, and 3,000 mu in forested areas. In typical fields, the density of the ten‑spotted armyworm ranged from 20 to 150 individuals per 100 steps; in Weichang County, where weeds are abundant and gray cress is prevalent on grassy slopes, the infestation was particularly severe, with some plots recording as many as 400 individuals per 100 steps.
　　In Jilin, the area affected by adult insects totals 9,000 mu, with 1,000 mu in farmland, 7,000 mu on grasslands, and 1,000 mu in forested areas. The average number of moths per 100 steps across all localities is 5, while Zhenlai County recorded the highest count at 140 moths per 100 steps.
　　In all parts of Heilongjiang, the number of rice stem borers per 100 plants was below 10, significantly lower than in the previous two years.
　　III. In some areas, first-generation eggs and larvae have been observed.
　　In Inner Mongolia, the area with egg deposits in the field totals 150,000 mu. In Hohhot, egg deposits cover 80,000 mu; in Tumed Left Banner and Wuchuan County, eggs were found on sugar beets, quinoa, and weeds, at an average of 2–5 eggs per square meter, with some beet fields reaching 200–300 eggs per square meter. In Baotou, egg deposits span 30,000 mu, with densities of 20–50 eggs per square meter in Donghe District and 6 eggs per square meter in Tumed Right Banner. In Bayannur City, Urad Middle Banner recorded an average of 4 eggs per square meter on June 20, with a maximum of 30; in Linhe District, findings were reported… Corn The groundsel plant has 250 eggs.
　　In Inner Mongolia, the area affected by larval outbreaks totals 100,000 mu, with Chifeng City, Ordos City, Hinggan League, and Hulunbuir City reporting 60,000 mu, 20,000 mu, 10,000 mu, and 6,000 mu, respectively. Among these, Chifeng City has an average pest density of 3–6 larvae per square meter; Ordos City… Corn The average pest density was 4–11 individuals per 100 plants; in Hinggan League, the average was 7 individuals per square meter; in Hulunbuir City, on grasslands, in forested areas, and around farmland, the average was 2–7 individuals per square meter, with pests at instars 1–2.
　　In Jilin, from June 19 to 21, egg masses and larvae were observed in the fields of Zhenlai County: two egg masses were found on Chenopodium album, containing a total of two eggs. In the first generation, larval damage was recorded on 0.1 ten-thousand mu of pastureland, with six first-instar larvae and two second-instar larvae.
　　In the farmland of Huinong District, Ningxia, the larval density was 0.4 larvae per square meter.
　　Given the grass cutworm’s propensity for outbreak‑induced damage and the high abundance of its overwintering sources abroad, all regions in northern China should closely monitor its population dynamics, conduct field surveys of adult moths, eggs, and larvae, issue timely forecasts, and provide guidance to farmers on effective control measures.