Cotton harvest aid products can favour the formation of structures that protect Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae) from insecticide application

Abstract Cotton, Gossypium hirsutum L., has an indeterminate growth habit. Therefore, the plant growing season leads to crops with a large amount of immature vegetative and reproductive structures, thus requiring the use of defoliants to promote the abscission of these structures and enable mechanical harvesting. However, the use of defoliants can negatively affect the development of immature fruits. This study examined the influence of defoliants, applied alone or in combination with each other, on the formation of dry and malformed reproductive structures of cotton, known as dry bolls, used as shelter by the boll weevil Anthonomus grandis grandis Boheman during cotton fallow periods. We investigated the influence of defoliants, applied alone, or combined with each other or with insecticide, on boll weevil mortality. In addition, we tested the susceptibility of boll weevils inside dry bolls to the action of insecticide. The results indicate that the defoliants can increase the number of dry bolls by up to 3.4 times, in relation to the control, 20 days after its application. The studied defoliants did not exert toxic effects on boll weevil when applied separately, nor synergistic effects of toxicity when combined with each other or with insecticides. At the end of the insecticide spraying experiments, the number of live boll weevils was 8.4 times greater when the insect was housed in dry capsules than when not housed. Defoliants can increase the formation of dry bolls, which can reduce boll weevil mortality due to insecticide application and hamper pest management.