A system for simulating the infestation of cotton plants by Agrotis segetum larvae in the laboratory

Author of the article:ZHANG Qian, GENG Ting, LU Yan-Hui

Author's Workplace：State Key Laboratory of Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China

Key Words：Agrotis segetum; larvae; cotton plant; root and stem; damage degree

Abstract：[Objectives]  Agrotis segetum Schiff is an important underground pest of cotton in Xinjiang, mainly feeding on the roots and stem. To facilitate research on the effects of A. segetum infestation on aboveground pests and natural enemies, we set up a system to simulate the infestation of cotton plants by A. segetum larvae in a laboratory. [Methods]  Different numbers of different instars of A. segetum larvae were introduced to cotton plants with either 3 or 5 true leaves, and confined to the root and stem of each plant. The optimal larval instar and density per plant was then determined based on the degree of plant damage. [Results]  Agrotis segetum larvae feed mainly on the phloem tissue of the roots and stems of cotton plant in spiral paths. The amount of damage to cotton plants was categorized into six levels; level 0, no evident damage; levels 1-4, in which the height of phloem damaged by larvae was classified as either ≤3 cm, between 3 cm and 5 cm, between 5 cm and 7 cm or ＞7 cm, respectively, and level 5 in which the plant was broken. The degree of damage to cotton plants infested with four, 2nd instar larvae was minor 3 days after infestation, (level 0-2). Plants infested with two, 5th instar larvae, or two, 6th instar larvae, sustained level 5 damage. Cotton plants with 3 true leaves infested with two, 3rd instar larvae, or plants with 5 true leaves infested with two 4th instar larvae sustained moderate damage (level 3-4). [Conclusion]  A system for simulating the infestation of cotton plants by A. segetum larvae was developed in a laboratory by infesting plants with 3 true leaves with two, 3rd instar larvae and plants with 5 true leaves with two, 4th instar larvae and allowing larvae to feed on the root and stem of each plant for 3 days. Although severely infested with A. segetum larvae, all plants in our study survived long enough to complete the experiment.