Colonização e dispersão intra-planta do bicudo-do-algodoeiro em lavouras de algodão

Abstract

Egg, larva and pupal stages of boll weevil develop inside cotton fruiting structures gaining protection against mortality factors. Therefore, the adult stage becomes the major target for control practices. The dispersal of boll weevil adults on the plant and throughout the cotton fields plus the knowledge about the lethal-time (LT) and residual control of recommended insecticides from different classes against adults of boll weevil were investigated aiming control decisions. Additionally, boll weevil colonization of cotton fields as function of border vegetation was determined using traps lured with boll weevil sex and aggregation pheromone glandlure. The traps were set up at field border (0m), 60, 120 and >200m inside the field and run 23 evaluations from 10 days after crop emergence (DAE) until crop defoliation. Newly-emerged weevils reach the cotton plant through the mainstream and exhibit their activities predominantely on the bottom part of the plants, where spent most of the time on bolls, followed by flower buds. The dispersal within-plant occurs mainly walking throught the fruiting branches and their leaves. Among the tested insecticides, the lowest LT was yielded with thiamethoxam, while the longest control residual was achieved with fipronil. The monitoring of commercial cotton fields showed that adult weevils were caught on pheromone traps during the first evaluation, 10 DAE, irrespective of bordering vegetation and distance from the border for all surveyed fields. Relatively low capture of weeivls and similar irrespective of field borders were observed on pheromone traps across all fields until boll maturation, when a significant increase in collections was noted and maintained until the end of monitoring. Based on the findings, we can infer that boll weevil behaviors colonizing the cotton plant minimizes its contact with treated surface despite the recommended insecticides were efficacious against the adults. Furthermore, the field colonization occurred as early as 10 DAE and do not occur only across the cotton field border and suggest that the precocious colonization is associated to the changes in the agricultural landscape such as adjacent crops and successive cotton cultivation.