Source Area of the Immigrant Population of Beet Webworm (Lepidoptera: Crambidae) in Northern Xinjiang, China

The beet webworm, Loxostege sticticalis (Linnaeus) (Lepidoptera: Crambidae), is a destructive pest inhabiting the northern temperate zone. In Xinjiang, China, this species has only occasionally infested certain areas, but has been causing severe damage since 2005. Early studies showed that most of the outbreak populations in northern Xinjiang are immigrant populations. However, the specific source area is still unknown. In this study, we determined the source area of the immigrant population of L. sticticalis in northern Xinjiang from 2010 to 2013 using daily monitoring data of L. sticticalis adults; we explained the causation of why an overwintering area of L. sticticalis could build up in Central Asia. Results showed that the direct source area of L. sticticalis in northern Xinjiang was eastern Kazakhstan, and the initial source area could be traced further to Altai Krai, Russia. Both regions were located at the foothills of the westernmost portion of Altai Mountains. The thermal conditions in these regions could not support L. sticticalis development for two generations before 1990. Hence, a few cocoons could be formed in the autumn. Influenced by global warming, L. sticticalis in these regions could complete two whole generations most years after 2001. The increased generation number, combined with sufficient precipitation, and mountainous terrain in the westernmost portion of Altai Mountains have created an overwintering area for L. sticticalis.