Aplicação seletiva, eficiênte e econômica do Malathion contra o Bicudo-do-algodoeiro e seu impacto sobre os inimigos naturais

Abstract

The cotton boll weevil, Anthonomus grandis (Coleoptera: Curculionidae) is the main insect pest of cotton in Brazil. The use of non-selective chemical insecticides such as malathion is the main tactic for controlling this pest. The objective of this research was to evaluate selective, efficient and economical application methods of malathion against the boll weevil and its effect on non-target insect pests and their natural enemies. The experimental design was randomized blocks, with four treatments and four replications (blocks). The treatments consisted of cotton plants sprayed with malathion (1,000 g.i.a. L-1) as follows: control (without spraying) (T1); weekly systematic spraying of all cotton rows with malathion insecticide after the appearance of cotton squares (T2), spraying of all cotton rows with malathion insecticide when the number of plants with cotton squares with oviposition punctures reached the level of 10% (RAMALHO et al., 1990) (T3); spraying alternate rows with the insecticide malathion when the number of plants with cotton squares with oviposition punctures reached the level of 10% (T4). The results obtained in this research made it possible to infer the following conclusions: (1) the number of cotton plants with cotton squares with oviposition punctures for the boll weevil is lower in all treatments sprayed with malathion, regardless of the way this product is applied; (2) malathion applied to cotton leaves is selective for the parasitoid B. vulgaris, but not for J. grandis; (3) malathion is not efficient in controlling aphid populations when applied to all cotton rows systematically or when the number of cotton squares with oviposition punctures reaches the level of 10%; (4) malathion is efficient in controlling aphid populations when applied to alternate rows of cotton because it preserves populations of its natural enemies that end up controlling this insect; (5) the highest gross and net revenues from cotton cultivation were in treatments sprayed with malathion, regardless of the form of application of this product and (6) malathion applied to all rows of cotton and in alternate rows, when the number of cotton squares with oviposition punctures reaches the level of 10% is more economical than that applied systematically.