Tratamento de sementes de algodão contra pragas sugadoras iniciais e interação com insetos predadores

Abstract

The seed treatment with insecticides is usually made with non-selective products as a recommended tactic to protect and∕or to reduce early-season insect infestation in cotton. In theory, this insecticide deployment is considered selective by making insecticide available in plant tissues, which is acquired by insect pests and not by natural enemies. However, non-target insects such as zoophytophagous natural enemies and pollinators can become contaminated when using plant products such as pollen, nectar and sap highlighting the importance of using selective insecticides. We assessed the cotton early-season sucking insect control and selectivity of cyantraniliprole (a selective diamide) and thiamethoxam (a non-selective neonicotinoid) through seed treatment (ST) and foliar application (FA). The insecticide residues on the plants were quantified at 12, 22, and 32 days after emergence (DAE) to assess the survival of the predators Orius insidiosus (Say) (zoophytophagous) and Eriopis connexa (Germar) (chewing) when confined on fresh plant surfaces treated either with insecticides used in FA or ST. Both insecticides had residues detected on plants but significantly reduced between 12 DAE and 22 DAE and, they were not detected at 32 DAE. Ciantraniliprole and thiamethoxam offered aphid suppression but with a more lasting effect with thiamethoxam. Both were not effective against high thrips infestation. Whitefly densities were variable across experiments, with economic threshold observed in all treatments after the expected plant protection with ST, including the untreated controls. The abundance of predators was higher in the control treatment, while treatments with thiamethoxam either ST or FA showed lower predator abundance. Cyantraniliprole ST and FA were compatible with O. insidiosus and E. connexa (>92% survival). Thiamethoxam was not toxic to E. connexa but highly toxic to O. insidiosus through dried residues from FA to ST (1.2% vs. 27.6% survival). Orius insidiosus still showed lower survival when exposed to thiamethoxam in FA compared to ST (51.4% vs. 89.3%) at 22 DAE. Regardless of the insecticides used and mode of use, there was no statistical difference in raw cotton yield across treatments.