Caracterização da atividade entomotóxica induzida pelo extrato metanólico de araucaria angustifolia em baratas da espécie phoetalia pallida

Abstract

We have demonstrated, for the first time, the insecticidal activity of Araucaria angustifolia methanolic extract (AAME) and one of its chemical secondary metabolites, quercetin against Phoetalia pallida. Preliminary investigation of AAME phytochemical compounds by thin layer chromatography showed the presence of quercetin. The total phenolic contents measured by spectrophotometry showed high content of phenolic acids (1,03%). High Performance Liquid Cromatography (HPLC) proved the presence of quercetin that was eluted at 10.6min. In doses ranging from 800-1200g/g (animal weight) AAME was effective to kill all cockroaches injected after 24 hours. Quercetin was more effective than AAME whole extract being lethal at 80g/g (animal weight). Both AAME (200μg/g of animal weight) and quercetin (40μg/g of animal weight) were able to induce a significative blockage at insect acetylcholinesterase activity. these compounds also induced increase in the time of grooming activity (138.11±5s /30min; p<0.05) and (2305s/30min; p<0.05), respectively. The injection of atropine (40μg/g) combined with quercetin (40μg/g of animal weight) significantly increased the grooming levels to over the control values of quercetin (3503s/30min; p<0.05). When methoctramine (40μg/g), a selective inhibitor of M2-M3 cholinergic receptor was combined with quercetin (40μg/g of animal weight) there was the highest increase on the grooming pattern (6008s/30min; p<0.01). When the SCH 23390 (40μg/g), a selective DA-D1 receptor blocker was administrated 15min earlier the treatment with quercetin (40μg/g) there was a significative inhibition of the grooming levels (906s/30min; p<0.05). Treatments with Tyramine (40μg/g) and Hydroxylamine (40μg/g), a Guanylate Cyclase (GC) induced a significative increase in the quercetin-induced grooming activity (20415s/30min; p<0.05) and (32515s/30min; p<0.01), respectively. Both AAME and quercetin were able to complete inhibit cockroach neuromuscular transmission in 120 min recordings (50±9% n=6; p<0.05) and (100±7% n=10; p<0.05), respectively . The later result, point out to a direct action of the extract on insect peripheral nervous system. The results presented here validate the insecticide activity of A. angustifolia methanolic extract in P. pallida. Phenolic compounds presents in this extract era likely to be involved in the insecticide activity of AAME. The mechanism of insecticide activity is complex and involve both Central and Peripheral Nervous System. The activation of events that initiate with the activation of Muscarinic Auto-receptors and/or cholinergic interneurons, could lead to an increase of cytosolic IP3 and Ca2+ concentration which could induce a dopamine release in the insect Nervous System. Concerning to the neuromuscular blockage, a further pharmacological investigation would be necessary to clarify this effect. However, one cannot disregard a direct action of quercetin on insect NMDA receptors.