Colonization and Spreading Ability of Artificially Released Coccinella Septempunctata in Tobacco Fields

In order to explore the effects of different environmental factors on the ability to colonize and spread of Coccinella septempunctata artificially released in tobacco fields, in 2019-2020, in Huilong Town, Mianning County, Liangshan Yi Autonomous Prefecture, Sichuan Province, research was carried out to analyze the hatching, spreading and retention of different insect stages of C. septempunctata in tobacco fields. The results showed that the hatching rate of egg masses released in the middle of the tobacco plants was 83.3%, which was significantly higher than the hatching rate released on the top and the bottom of the tobacco plants, and but not significantly different from the hatching rate of the indoor experiments. The hatchability of egg masses released in cloudy days was 91.1%, significantly higher than rainy days, and but not significantly different from that of in indoor environments and in sunny days. When the distance between the first larvae and the target tobacco plant is greater than 0.55 meters, the insect couldn't spread to the target tobacco plant, and the young larvae stayed on the target plant for 7 days. The residence time of adults released in overcast days reached 40 h on the target tobacco plants. Adult dispersal distance reached 150 m. In conclusion, cloudy days are the best weather for releasing C. septempunctata, and the middle part of the tobacco plants is the best part for releasing C. septempunctata eggs.