Resistência de genótipos de milho a Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae)

Abstract

Spodoptera frugiperda is a highly polyphagous species, economic damage to various agricultural crops, especially in maize. Thus, the present study aimed to evaluate the resistance categories of S. frugiperda maize genotypes through attractiveness, consumption and biological aspects, in antibiosis and non-preference tests for food, with and without a choice . For the creation of S. frugiperda, insects were collected from maize crops in the city of São Luís-MA, which were kept and multiplied in the Laboratory of Entomology of the State University of Maranhão. The corn genotypes used were: AG1051, BRS 2022, BRS 4104, BRS 4103, BM 207 and BRS Caatingueiro that were grown in plastic pots with black soil and bovine manure under greenhouse conditions. For the antibiosis test, a completely randomized design with six treatments and 50 replicates was used. Newly hatched larvae were fed with leaves of the maize genotypes and kept in an air-conditioned room until reaching the pupae stage. The pupae formed were collected, sexed, weighed in analytical balance and placed in PVC tube cages (10 cm in diameter x 21 cm in height), the emerged adults were grouped in couples in a ratio of 1: 1. The evaluations were initiated 24 hours after the installation of the experiment, were analyzed: larval phase (weight at 7 and 14 days, duration and viability); pupal phase (weight after 24 hours, duration, viability and percentage of deformation) and adult phase (number of eggs / female, longevity of males and females). In the non-preference food test with and without a choice, two freshly hatched caterpillars were used per variety and a 3rd instar caterpillar per variety were used in both tests in which the attractiveness of the caterpillars was evaluated at different time intervals and leaf area consumed. The experimental design was randomized blocks, with six treatments (genotypes) and ten replications, and the experimental design was completely randomized, with six treatments and twenty replicates. In both tests the evaluations were initiated 72 hours after the release of the couples and the data obtained under variance (ANOVA) by the F test, the means compared by the Tukey test at 5% probability. The data obtained in the non-preference tests were submitted to the normality test and compared by the non-parametric Kruskal-Wallis test. The results obtained in the antibiosis test at both 7 and 14 days showed a significant difference between the maize genotypes studied. The duration of the larval period was higher in caterpillars fed AG1051, BRS 4103, BRS Caatingueiro and BRS 2022 genotypes. Genotype AG1051 provided the lowest weight of male and female pupa differing significantly from BRS 4103, which resulted in higher weight. In the food preference test there was a significant difference in the attractiveness of first instar caterpillars of S. frugiperda in the test with no chance of choice, the lowest number of caterpillars was verified in genotypes BRS 4104 and BM 207. In the test with a choice of third caterpillars instar of S. frugiperda, it was observed that genotype BRS 4104 showed the highest attractiveness of caterpillars when compared to BRS 4103. Leaf mass consumed by caterpillars the lowest consumption was observed in genotype BRS 2022 and the highest consumptions observed in genotypes AG 1051 and BRS 4103. The AG1051 genotype shows resistance characteristics in the antibiosis category to S. frugiperda, due to lower larval and pupal weights, lower number of eggs / female and eggs / female posture and lower longevity of S. frugiperda males