ABSTRACT
Insect pests are one of the factors that most impact plant yield. The magnitude of the losses and the spatiotemporal pest distribution in crops is a result of their interactions with the environment. Therefore, the understanding of the causes of production losses and the pest spatial patterns is important for the development of suitable sampling plans and pest management programs. Thus, this study aimed to quantify grain losses caused by insects and to determine the spatial distribution pattern of arthropod pest species in Bt and non-Bt corn. The prevailing insect pests in the corn ears were the earworm and fall armyworm caterpillars (Helicoverpa spp. and Spodoptera frugiperda), the cornsilk fly (Euxesta spp.), the maize weevil (Sitophilus zeamais), and the square-necked grain beetle (Cathartus quadricollis). The non-Bt corn was more attacked by the caterpillars and the weevil, while Bt corn was more affected by the cornsilk fly Euxesta spp. Spatial dependence was significant for the damage caused by the caterpillars, the grain beetle and the maize weevil in both the Bt and non-Bt corn genotypes. The range of the damage caused by the insects was between 9.0-9.7 m for the caterpillars, 6.9-12.20 m for the cornsilk fly, 10.7-80.4 m for the square-necked grain beetle, and 51.9-170.7 m for the maize weevil. The pattern of the spatial distribution of pest damage in both corn genotypes (i.e., Bt and non-Bt corn) was similar with a prevalence of moderate to strong spatial dependence and aggregate damage distribution. The plants near to the sampling points exhibited injury and infestation levels similar to those of the sampled plants.
Subject(s)
Bacterial Proteins/genetics , Bacterial Proteins/toxicity , Endotoxins/genetics , Endotoxins/toxicity , Hemolysin Proteins/genetics , Hemolysin Proteins/toxicity , Insecta/pathogenicity , Zea mays/genetics , Zea mays/parasitology , Animals , Bacillus thuringiensis Toxins , Brazil , Coleoptera/pathogenicity , Diptera/pathogenicity , Edible Grain/genetics , Edible Grain/parasitology , Genotype , Herbivory , Moths/pathogenicity , Pest Control, Biological/methods , Plants, Genetically Modified , Spodoptera/pathogenicity , Weevils/pathogenicity , Zea mays/growth & developmentABSTRACT
A conservação de inimigos naturais é um componente fundamental no manejo integrado de pragas. Neste trabalho, estudou-se a seletividade de sete inseticidas usados no manejo de Plutella xylostella (L.) (Lepidoptera: Plutellidae) ao parasitóide Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae) e aos predadores Discodon sp. (Coleoptera: Cantharidae) e Lasiochilus sp. (Hemiptera: Anthocoridae). Os organofosforados metamidofós e paratiom metílico e o carbamato carbaril foram altamente tóxicos aos três inimigos naturais estudados. Dimetoato apresentou seletividade em favor do Discodon sp., na dose e subdose. O inseticida acefato apresentou alto impacto ao Discodon sp., no momento da aplicação e seu efeito foi reduzido com a metade da concentração do princípio ativo. Deltametrina apresentou seletividade à O. sokolowskii nas duas dosagens. Já permetrina foi seletiva a Lasiochilus sp., somente na subdose. Discodon sp. foi mais tolerante à dose e subdose do dimetoato e à subdose do acefato do que O. sokolowskii e Lasiochilus sp. O predador Lasiochilus sp. foi mais tolerante à dose e subdose da permetrina do que O. sokolowskii e Discodon sp. O parasitóide O. sokolowskii foi mais tolerante à dose e subdose da deltametrina do que Lasiochilus sp. e Discodon sp. Os resultados desta pesquisa foram obtidos em condições de exposição extrema, portanto indicam que os inseticidas seletivos possivelmente não serão prejudiciais aos inimigos naturais, em condições de campo.
The conservation of natural enemies is a fundamental component in the integrated pest management. In this work, one studied the selectivity of seven insecticides, used in the management of Plutella xylostella (L.) (Lepidoptera: Plutellidae), to the parasitoid Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae), and to the predators Discodon sp. (Coleoptera: Cantharidae) and Lasiochilus sp. (Hemiptera: Anthocoridae). The organophosphates methamidophos and methyl parathion, and the carbamate carbaryl showed high toxicity to the three natural enemies studied. Dimethoate showed selectivity in favor of Discodon sp. in the dose and sub-dose. The insecticide acephate showed a high impact on Discodon sp. at the time of the application, and its effect was reduced with half of the concentration of the active ingredient. Deltamethrin showed selectivity to O. sokolowskii in both dosages. Permethrin was selective to Lasiochilus sp. only in the sub-dose. Discodon sp. was more tolerant to the dose and sub-dose of dimethoate and to the sub-dose of acephate than O. sokolowskii and Lasiochilus sp. The predator Lasiochilus sp. was more tolerant to the dose and sub-dose of permethrin than O. sokolowskii and Discodon sp. The parasitoid O. sokolowskii was more tolerant to the dose and sub-dose of deltamethrin than Lasiochilus sp. and Discodon sp. The results of this research were obtained in conditions of extreme exposition. Thus, the results indicate that it is probable that the selective insecticides will not be harmful to the natural enemies in the field.
