Responses Of The Beet Webworm, Loxostege Sticticalis L. (Lepidoptera: Pyralidae) To The Climate Warming In Northern China

The beet webworm, Loxostege sticticalis L. (Lepidoptera: Pyralidae) is one of the most destructive pests of crops and fodder plants in northern China. It had broken out for three periodicities since the founding of People's Republic of China in 1949 and led to huge economic loss to agriculture and pasturage. In the 3rd outbreak periods (from 1996 on) new characteristics such as increasing of damge areas and damge degree, higher elevation and latitude shift of damge areas and overwintering ground appeared. In order to explain the damge and occurrence mechanism, reform and promote the forecasting and controlling abilities of L. sticticalis, based on ecological principle and methodology, combined with analysis of climate change and occurrence and damage data of L. sticticalis in China about 30 years, we revealed the effect of climate warming on first moth caught date (FMCD), last moths caught date (LMCD) and annual moth occurrence periods (AMOP) of L. sticticalis, and studied the relationship between population dynamics, overwinter source and overwinter ground distribution of L. sticticalis and climate warming. Some new results were gained mainly as follows:It was revealed that damage area of L. sticticalis in China was the most significant district about climate warming all around the country. By analyzing climate warming from 1979 to 2008 among 604 weather stations all over the country, we found that climate warming of the damage area of L. sticticalis (district north off the 12℃isotherm of annual mean temperature) was the most significant compaired with that of other districits, which, with mean increasing tendencies of 0.06℃/a among spring, summer, autumn and winter, was 1.5 to 3 times faster than that of other districts. Further more, mean annual temperature of this district increased rapidly, with a mean tendency of 0.07℃/a, obviously faster than other districts especially the southern district. These results were consistent with researches in and abroad.Advancement of FMCD, postponed of LMCD and prolonged of AMOP was revealed. FMCD of Kangbao (114.60°E, 41.80°N), Datong (113.20°E, 40.06°N) and Siziwangqi (111.41°E, 41.32°N) during 1979-2008 took on a significant advanced trend, which was 0.40d/a, 0.47d/a and 0.74d/a on average respectively. The beginning of peak moth periods, peak moth periods, and the last peak of moth periods of L. sticticalis of Kangbao, Datong and Siziwangqi during 1979-2008 didn't display any significant advanced or postponed tendency during 1979-2008. LMCD of Kangbao, Datong and Siziwangqi during 1979-2008 showed a significant postponed tendency of 1.69 d/a, 1.02 d/a and 0.83 d/a respectively. While AMOP of Kangbao, Datong and Siziwangqi during 1979-2008 exhibited a significant prolonged tendency of 2.09 d/a, 1.49 d/a and 1.49 d/a respectively.It was revealed that local climate warming was the main factor of moth phenology shift. By using of correlation analysis, we test the correlation between moth phenology like FMCD, LMCD and AMOP of Kangbao, Datong and Siziwangqi during 1979-2008 and local mean temperature of different time periods. The results showed that 1) Advancement of FMCD was related to temperature rising in spring. Advancement of FMCD in Datong was due to TMar.-May (mean temperature from March to May) rising. Whie Advancement of FMCD in Kangbao and Siziwangqi was due to TApr.-May and TMar.-Apr. rising respectively. 2) Postponed of LMCD was related to temperature rising in autumn, and the relation varied among different locations. Postponed of LMCD in Kangbao and Siziwangqi was due to TAug. , TJul.-Sep. and TAug.-Sep. respectively. 3) Prolonged of AMOP was related to temperature rising from spring to autumn. Prolonged of AMOP in Kangbao and Siziwangqi was due to TMar.-Aug. , TApr.-Sep. , and TApr.-Sep. respectively. All these result explained that climate warming was one of the main causes of moth phenology shifts of L. sticticalis, but the relation between temperature changes and moth phenology shifts varied among different locations, which would promote and reform forecasting and controlling of this insect in China to some degree.Responses of moth caught amount and damage area of larvae of L. sticticalis to climate warming were revealed. By compairing annual moth caught amount of Kangbao, Datong and Siziwangqi, we found that for the low latitude and high temperature site like Datong (Altitude 1000 m), annual moth caught amount decreased with climate warming year by year. But for the higher latitude, higher altitude and lower temperature sites like Kangbao and Siziwangqi (Altitude > 1400 m), annual moth caught amount increased with climate warming year after year. These results showed that the occurrence and damage of L. sticticalis trended to shift to higer latitude and altitude. By analyzing damage area of L. sticticalis and climate warming of main damage and occurrence area from 1953 to 2008, we found that annual damage area, increased by 571,000 ha every 10 years, was significantly correlated with TMay-Aug. of main damage and occurrence area of L. sticticalis larvae, increased by 0.25℃every 10 years.Responses of overwinter mechanism of L. sticticalis to climate warming in China were revealed. 1) Relationship between the area and extension of overwintering ground and climate warming during the 2nd and 3rd outbreak period of L. sticticalis were studied. Compared with the 2nd outbreak period, we found that the area of overwintering ground of the 3rd outbreak period was obviously larger, and the north line of overwintering area of the 3rd outbreak period was further to the north, and the mean latitude of the top 10 investigation points in latitude in 3rd outbreak period was 5.29°higer, all of which was resulted from climate warming in the 3rd outbreak period of L. sticticalis to some extent. 2) It was revealed that diapause rate of first generation larvae of L. sticticalis from 1956 to 1959 and from 1982 to 1984 in Kangbao was negatively correlated with local mean temperature from Jun 10th to Jul. 31st, meanwhile mean temperature from Jun 10th to Jul. 31st of Kangbao from 1956 to 2009 rose 0.026℃/a, which might have led to the decrease of diapause rate of first generation larvae of L. sticticalis. 3) Relationship between survival rate of overwinter larvae of Siziwangqi and climate change was studied. Based on correlation analysis, we found that survival rate of overwinter larvae of Siziwangqi from 1996 on was positively correlated with local winter temperature. That was to say the higer the winter temperature was, the higher the survival rate of overwinter larvae was.