Bioatividade de extratos vegetais no controle de Sitophilus oryzae (Linné, 1763) em arroz

Abstract

The continuous growth of the world population, intensive competition among humans and plant pests for the same food sources, the resistence to existing inseticides by some insects and the persistence of residues in the environment and food created the necessity for new insecticides. In this research field, vegetable species appear as a promising source of new metabolites with insecticide activity. In the case of stored rice, the most important insect pest in the State of Rio Grande do Sul is the weevil Sitophilus oryzae (Linné, 1763). In order to explore plants with potential insecticide activity against this insect, several plant extracts were tested in the Federal University of Santa Maria (Santa Maria, RS). In a laboratory were evaluated the mortality rate, repellence and adult emergence of Sitophilus oryzae in hulled rice (Oryza sativa L.) treated with powder of Piper nigrum L., Chenopodium ambrosoides L., Nicotiana glauca Graham, Nicotiana tabacum L., Corymbia citriodora Hook., Trichillia catigua A. Juss , Melia azedarach L., Mentha pulegium L., Calopogonium caeruleum Hemsl., Ricinus communis L., and Ruta graveolens L. As standard were used Pyrimifos-methyl, Deltametrin and Diatomaceous Earth. The powder that caused the highest mortality rates was from C. ambrosoides.. The insecticides used as standard were more effective than the vegetable powders. As repellent, powder of Corymbia citriodora was the most effective and as adult emergence inhibitor, none presented a significant effect. As for the species that presented the highest insecticide activity, C. ambrosoides and C. caeruleum, the LD50 was 0.1999g/20g of rice and 0.254g/20g of rice respectively. This work also aimed to determine the damages caused by Sitophilus oryzae in rice using four insect populations in hulled rice samples and the populational growth at four grain moisture levels. It was observed that damage levels increased linearly with insect population althought consumption per capita was higher at lower populations. There was in increase in insect population as grain moisture increased up to 14,9% (U.B.) and the reafter decreased.Other experiment aimed to test the insecticide activity of aquous extracts of Chenopodium ambrosides and Calopogonium caeruleum compared to Artemia salina Leach. This microcrustaceous is used as toxicity bioindicator of chemical substances, agrochemicals, pollutants and other products. The LC50 of Chenopodium ambrosoides and Calopogonium caeruleum was found to be 1.76 mg/ml and 4.78 mg/ml respectively. In order to investigate the acute oral toxicity of the aquous extracts and analyse the biochemical and histological parameters in rats the plants was studied: Chenopodium ambrosoides and the Calopogonium caeruleum. For C. ambrosioides, the group of the males did not only present difference statistics for creatinina, whereas, for all the other parameters had differences between the treat groups and the control. The C. caeruleum presented statistical differences for creatinina, TGO and TGP, in both the sexs, with exception of the urea in the group of the females. In the results of the histopathological studies, the extract of C. ambrosoides of both concentrations, in the males provoked discrete liver cellular swollen, already with C. caeruleum 9%, in the males, verified discrete sclerosis to glomerular and discrete liver cellular swollen in the group of the females.