ABSTRACT
The cotton plant, Gossypium hirsutum, hosts various pests that damage different structures. Among these pests, Spodoptera cosmioides (Walker) and Spodoptera eridania (Cramer) (Lepidoptera: Noctuidae) are considered important. The objectives of this study were to characterize and to quantify the potential damage of S. eridania and S. cosmioides feeding on different structures of cotton plants. For this purpose, newly-hatched larvae were reared on the following plant parts: leaf and flower bud; leaf and boll; flower bud or boll; and leaf, flower bud and boll. The survival of S. cosmioides and S. eridania was greater than 80 percent and 70 percent for larvae fed on cotton plant parts offered separately or together, respectively. One larva of S. eridania damaged 1.7 flower buds, but did not damage bolls, while one larva of S. cosmioides damaged 5.2 flower buds and 3.0 cotton bolls. Spodoptera eridania and S. cosmioides can be considered species with potential to cause economic damage to cotton plants because they can occur throughout cotton developmental stages causing defoliation and losses of reproductive structures. Therefore, the results validate field observations that these two species of Spodoptera are potential pests for cotton.
Subject(s)
Animals , Gossypium/parasitology , Spodoptera/physiologyABSTRACT
O pulgão Aphis gossypii Glover é vetor da Virose Mosaico das Nervuras (V.M.N.), que pode ocasionar na cultura do algodoeiro, produção reduzida ou nula. O objetivo do estudo foi identificar cultivares de algodoeiro resistentes a V.M.N. quando expostas à ação de pulgões. Os experimentos foram conduzidos na fazenda experimental do Instituto Agronômico do Paraná, IAPAR, Londrina, PR, sendo o delineamento estatístico em blocos casualizados. As cultivares comparadas foram: Delta Opal, Deltapine A90, CNPA ITA 90, Coodetec 401, IAC 22, IPR 95, IPR 96 e IPR 94. Para avaliação foram selecionadas 25 plantas observando-se a presença de pulgões e sintomas de V.M.N. Dois experimentos foram realizados nas mesmas condições, sendo que em um deles realizaram-se aplicações de inseticidas, para o controle dos pulgões, quando sua presença foi constatada em 10 por cento das plantas. O outro experimento não recebeu aplicação de inseticidas para controle de pulgões. A presença do vetor foi constatada em plantas de todas as cultivares. Observou-se que, mesmo com menor infestação de pulgões na cultivar CNPA ITA 90, ocorreram elevados índices de V.M.N. com redução de 68 por cento da produção quando comparada com Delta Opal. As cultivares Delta Opal e Coodetec 401 mostraram-se muito resistentes a V.M.N. pela ausência de plantas com sintomas, IAC 22 foi susceptível, enquanto Deltapine A90 e CNPA ITA 90 foram muito susceptíveis. Os inseticidas ofereceram proteção razoável à ação do vetor, mas os dados permitem inferir que em áreas com elevados níveis de infecção de V.M.N., o método de controle mais adequado seria a adoção de cultivares resistentes à enfermidade como Delta Opal e Coodetec 401.
The aphid Aphis gossypii Glover is a vector of Cotton Vein Mosaic Virus (V.M.N.), which can cause reduced or null yields in cotton crops. The objective of this study was to identify cotton cultivars resistant to V.M.N. when exposed to the action of aphids. The experiments were conducted at the experimental farm of the Instituto Agronômico do Paraná, IAPAR, in Londrina, PR, Brazil, in a randomized blocks statistical design. The cultivars compared were: Delta Opal, Deltapine A90, CNPA ITA 90, Coodetec 401, IAC 22, IPR 95, IPR 96, and IPR 94. Twenty-five plants were selected for evaluation; the presence of aphids and V.M.N. symptoms were recorded. Two experiments were conducted under the same conditions; in one of them, insecticides were applied to control aphids when their presence was detected on 10 percent of the plants. The other experiment received no insecticides for aphid control. The vector was present on the plants from all cultivars. High V.M.N. rates occurred in cultivar CNPA ITA 90 even under lower aphid infestations, with a yield reduction of 68 percent when compared with Delta Opal. The cultivars Delta Opal and Coodetec 401 proved very resistant to V.M.N. based on the absence of plants with symptoms; IAC 22 was susceptible, while Deltapine A90 and CNPA ITA 90 were very susceptible. The insecticides provided reasonable protection against the action of the vector, but data allowed to infer that in areas with high levels of V.M.N. infection, the most suitable control method would be the adoption of cultivars resistant to the disease, such as Delta Opal and Coodetec 401.