Efeitos dos extratos aquosos de Bidens pilosa Linné e Mikania glomerata Sprengel (Asteraceae) sobre aspectos biológicos e comportamentais de Subulina octona (Bruguière,1789) (Mollusca, Subulinidae)

Abstract

The land snail Subulina octona (Bruguière, 1789) is an intermediate host of helmints that parasitizes humans and domestic animals. In high densities it can also be a crop pest making necessary the application of control measures. The search for plant molluscicide increased in last years due to its advantages. The plants Bidens pilosa Linné and Mikania glomerata Sprengel are widely distributed and are frequently used in folk medicine. They have active principles that are water soluble and with proven action against snails. The aim of this study was to confirm the presence of these active principles, to calculate the reference concentrations (LC50 e LC90) in adult S. octona and to evaluate the effects of the LC50 obtained on biological and behavioral aspects of this snail in different development phases. To obtain the LC50 e LC90 five concentrations were utilized for each plant aqueous extract, and 30 snails (10snails/group) were utilized for each concentration and for control group. The groups were exposed to 5mL of the extracts by direct contact with the solution for 24 hours followed by 24 hours of recovery period and the control groups were exposed to distilled water for the same time period. The reference concentrations were obtained using the Probit analysis through (BioStat 2008 software, version 2.5). The LC50 obtained were tested on eggs, newly hatched, 30 day old individuals and adults that were exposed to the treatments for 24 and 48 hours period. Control groups were exposed to distilled water. For the adults, were utilized three applications of the LC50 every 30 days. The observations to analyse the repellency in adults were made at the realized at the 10 first minutes after the first application. The hatchability, survival and reproduction were evaluated and the data were compared by using the Kruskal-Wallis (p<0,05) (BioEstat software, version 5.0). The phytochemical analysis confirmed the presence of flavonoids, tannins and saponins in the aqueous extracts of both plants. The LC50 and LC90 obtained for B. pilosa was 51.4mg/mL and 74.1mg/mL respectively, and for M. glomerata was 44.6mg/mL for LC50 and 71.9mg/mL for LC90. The repellency of the extracts was verified after the application. The survival of adult snails was signficantly diminished after the second application of the extracts. In the same way, the fecundity was reduced in groups exposed for 24 hours. It was not verified significantly difference in offspring hatchability from adult snails exposed to the treatment. However, the eggs exposed directly to the treatments had significantly reduction in hatchability means. The mean hatchability of the snail from eggs directly exposed to the treatments were significantly reduced. The extracts also influenced the survival of snails hatched from treated eggs, in newly hatched and 30 day old individuals. Alterations on growth were verified in all treatments. The results obtained in this study were probably due to the complex combination of the active principles that can interact synergistically, aditive or antagonist or even facilitating absorption of some compounds. The facility in the plant collection, extract preparation and application of these extracts turn these plants candidates in the control of this species.