Bemisia Tabaci Densities On Cotton And Predatory Insects

The sweetpotato whitefly, Bemisia tabaci (Gennadius), is a pest of primary importance of cotton (Gossypium hirsutum L.) in Mexico because it negatively affects yield and fiber quality. vThis study was conducted with the objective of determining the densities of the sweetpotato whitefly in cotton, and its relationship to the distance to cantaloupe fields, use of insecticides, yield, and quality of cotton lint; as well as determining the abundance of predatory insects and their relationship to the densities of the sweetpotato whitefly. Populations of whitefly adults and nymphs were recorded weekly by visual inspection of the underside of the fifth main-stem leaf from cotton plant terminal in six cotton fields located 300 to 23,200 m away from cantaloupe fields, from 29 May to 27 August 2019. Predatory insect densities were sampled weekly with a sweep net. The number of insecticide applications, seed cotton yield, and lint quality were obtained in each cotton field. A negative relationship between whitefly densities in cotton and distance to cantaloupe fields was observed. Cotton fields close to cantaloupe fields (300 to 1400 m) had high whitefly populations (average of 27.1 adults/leaf); while distant cotton fields (13,600 to 23,200 m) had low whitefly populations (average of 3.2 adults/leaf). Seed cotton yield, as well as lint length, fineness, and strength were not significantly affected by observed whitefly densities. The white color of the cotton lint (reflectance value, Rd) was significantly reduced by increasing the density of whitefly adults and nymphs during the time of open boll formation. Thirteen species of predatory insects were found, with Chrysoperla sp., Orius sp., Hippodamia convergens Guerin-Meneville, and Chrysopa sp. being the most abundant. The cotton fields with 10 to 12 insecticide applications had lower densities of total predatory insects (10.3 to 10.8 predators per 100 sweeps), compared to those with 2 to 7 insecticide applications (22.3 to 75.5 predators per 100 sweeps). A positive (r = 0.54 to 0.89) and significant correlation was found between whitefly densities and those of Orius sp., Chrysoperla sp., Chrysopa sp., and total predators, indicating a good density-dependence relationship between these predators and their prey. Th results indicated need for proper management of the whitefly in cotton, considering the distance to melon-producing areas, the negative effect of abundant pests on fiber color, which has caused punishment or discounts on price, and conservation of beneficial entomofauna by using selective insecticides.