Influência de fatores climáticos na dinâmica populacional de Bemisia tabaci (Gennadius, 1889) e Anthonomus grandis (Boheman, 1843) em algodoeiros Bt e não Bt no Estado de Mato Grosso do Sul

Abstract

Agriculture is highly dependent on climatic factors, so climate change can affect agricultural production in many ways. For example, the occurrence of pra-gas in large crops in Brazil has become even more serious due to climatic variations. Insects are among the organisms most likely to be affected by climatic variations because the climate has significant control over their development, reproduction, and survival. The cotton Gossypium hirsutum L. (Malvales: Malvaceae) is a crop that attracts and harbors a large number of insect pests that affect the plants from the roots to the capuchins, affecting the productivity and important characteristics of the fibers, making it impossible the culture reaches its maximum productive yield. Among the main pests we can mention the cotton boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae) and the whitefly, Bemisia tabaci Gennadius (Aleyrodidae: Hemiptera). In this sense, the objective of this work was to relate the population dynamics of A. grandis and B. tabaci adults to climatic factors (mean temperature, mean humidity and rainfall) in Bt cotton cultivars compared to non-Bt cultivars. The experiments were carried out in the Brazilian Midwest region which is considered to be the main national cotton producer. In the municipalities of Maracaju, MS and Chapadão do Sul, MS. In Maracaju the experiment was established at the MS Foundation Experimental Station in Chapadão do Sul at the Chapadão Foundation. Each field in both municipalities consisted of three sample areas of 25m x 60m, each sampled area being seeded with different cotton cultivars: two fields with Bt (NuOpal® and WideStrike®) and one field with conventional cotton (DeltaOpal®). In the sampling areas in Maracaju, no applications of insecticides were made, in Chapadão do Sul there were insecticide applications whenever the key pests reached the population level of control. The evaluations were distinct for each insect evaluated and consisted in the visual inspection of the plant by noting the number of adults of A. grandis per plant and the number of plants with B. tabaci. Ten samples were taken in each sampling area every two days, in Maracaju the evaluations were in the months of February and March of 2017, and in Chapadão do Sul occurred in the months of March to April of 2017. The evaluated plants were selected in a way completely random, with 50 plants being inspected in each sample field. The meteorological data were recorded during the entire evaluation period in both municipalities. The adult infestation of B. tabaci in Maracaju was higher (33.46), compared to South Chapadão (5,30). The infestation of A. grandis. was higher in Chapadão do Sul (16.20) than in the municipality of Maracaju (3.43). Probably, the applications of insecticides carried out in the Chapadão do Sul areas efficiently controlled whiteflies, but were not efficient in controlling cotton boll weevil, probably due to differences in insect biology and to the fact that numerous applications of insecticides, this insect being able to evolve resistance to the chemicals used. Regarding the climatic factors, it was verified that rainfall has a strong negative correlation with the population of B. tabaci in the two study sites; since atmospheric humidity has a strong negative correlation with the adult population of A. grandis in both municipalities. Therefore, it is expected that, in years of high precipitation and / or atmospheric humidity during the crop development period, there is a low incidence of these pests.