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.

Infestation of Anthonomus grandis grandis (Coleoptera: Curculionidae) contributes to forming shelter structures in cotton plants

“…Consequently, harvesting and processing costs are increased and fibre quality and profitability are reduced . Weevil infestation almost doubled the number of dry bolls compared to the control, but the presence of these structures in non-infested plants (control treatment) demonstrates that other factors are also involved in the production of dry bolls (do Vale et al, 2023;Osekre et al, 2009;Srivastava et al, 2010).…”

“…In addition, the greater the resources during the weevil immature stage, the better the protection granted from the external environment, such as harsh temperatures and humidity (Pires et al, 2017;Ribeiro et al, 2010). Many arthropods benefit from the favourable microclimates provided by plant shelters to endure periods hostile to their survival (Connor & Taverner, 1997;Giron et al, 2016;Tooker & Giron, 2020), and so, the boll weevil exhibits greater survival during adverse conditions when protected inside dry bolls (do Vale et al, 2023;Greenberg, Showler, et al, 2004;Summy et al, 1993).…”

“…Only part of the boll weevil population, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), survives during the cotton off-season in dry and deformed cotton fruits, known as dry bolls (do Vale et al, 2021;Greenberg, Showler, et al, 2004;Ribeiro et al, 2015). The weevil inside the dry boll is protected from pesticides, natural enemies and the heat and drying of the soil surface, thereby increasing its survival and its reproduction capability (do Vale et al, 2023;Greenberg, Showler, et al, 2004;Summy et al, 1993). However, the relationship between boll weevil and dry boll formation is little understood.…”