Mortalidade do bicudo em algodoeiros irrigados por gotejamento e aspersão

Abstract

The cotton boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae) is considered the main cotton pest in Brazil. However, immature weevil stages are known to be vulnerable to adverse climatic factors, such as high temperatures and low soil moisture, which act by dehydrating cotton squares fallen on the ground and causing high mortality rates at different stages of development of cotton boll weevil that are housed within these structures. The objective of this research was to evaluate the mortality of cotton boll weevil in drip and sprinkler irrigation systems. The work was developed at the Embrapa Cotton Entomology Laboratory and in the experimental fields of this institution, located in Campina Grande, PB and Barbalha, CE. The experimental design was randomized blocks with two treatments: (1) drip irrigated cotton and (2) sprinkler irrigated cotton, distributed in sixteen replications. The experimental unit consisted of one emergence cage of cotton boll weevil adults containing 37 cotton squares with punctures of oviposition, open and yellowish bracts, installed between two rows of cotton by irrigation system. The average number of boll weevil emerged from cotton squares and the causes of mortality of the different stages of development of the boll weevil that did not emerge from cotton squares were determined in each treatment. Third generation life tables of boll weevil were also constructed, using natural mortality data recorded in drip and sprinkler irrigation treatments and quantifying the actual, apparent and indispensable mortality rates and the lethal power of each cause of mortality. The results showed that: (1) there is no emergence of boll weevil adults from punctured cotton squares by oviposition in the soil surface in the drip; (2) the number of boll weevil adults emerging from punctured cotton squares by oviposition on the soil surface per cage in irrigation sprinkler system was higher than those emerged from these plant structures in the irrigation drip system; (3) the major contribution to the causes of natural mortality of the boll weevil was due to desiccation in both irrigation systems, followed by the number of unviable eggs; (4) the combination of high temperatures and low relative humidity recorded in both treatments is responsible for the high mortality rates of egg and larvae of the boll weevil by desiccation; (5) desiccation mortality showed the highest lethal power (Kxc) among the mortality causes of immature boll weevil stages within cotton squares in both irrigation systems and (6) the drip irrigation system can be used in areas cultivated with cotton in the Brazilian semiarid to control of the boll weevil.