Systemic insecticides in cotton plants: seed treatment, protection against early-season sucking insects, and their ecological selectivity with predatory insects of different feeding habits

Abstract

We tested the hypothesis that systemic insecticides should be effective against sap-sucking insects which acquire toxicants from the tissues of treated plants whereas their natural enemies should be unaffected. Under this hypothesis, the suppression of early-season cotton insect infestations and the interaction with predatory insects of different feeding habits were investigated using the systemic insecticides cyantraniliprole and thiamethoxam through foliar application (FA) and seed treatment (ST). Insecticide residues on ST plants were quantified at 12, 22, and 32 days after emergence (DAE) to assess the survival of the zoophytophagous (Orius insidiosus) and chewing (Eriopis connexa), both predators of early-season cotton pests, when confined on treated plant material. Residues of both insecticides were detected on ST plants, but the level was significantly reduced between 12 and 22 DAE and not detected at 32 DAE. Both insecticides offered aphid suppression but with a more prolonged effect of thiamethoxam, and both were ineffective against high thrips infestation. Whitefly densities were at or below economic threshold in all treatments after the expected control provided through ST. Cyantraniliprole was compatible with both predators (> 92% survival) through FA and ST. Thiamethoxam was highly toxic to O. insidiosus through FA (0.5% survival) and diminished through ST (27.6% survival). At 22 DAE, O. insidiosus still showed lower survival with FA than ST with thiamethoxam (51.4% vs. 90.7%). Regardless of the insecticide used in ST, supplementary FA was required against early-season pests. The results show that ecological selectivity through seed treatment depends on the feeding habit of the predator and the insecticide applied.