Stomoxys calcitrans: estabelecimento de colônia e efeito de Metarhizium anisopliae sobre seus estágios imaturos

Abstract

Stomoxys calcitrans is a hematophagous fly that is related to reduction in animal production due to the stress and dissemination of pathogens. The knowledge in plague control, using entomopathogenic fungi, has been growing year by year, but few works have been done to control S. calcitrans. The aims of this study were rearing a colony of S. calcitrans to make a bioassay of microbial control, verify the pathogenic potential of Metarhizium anisopliae in eggs, larvae and pupae and access three methods of egg s exposition to the studied fungi. After methodologies adaptation of rearing S. calcitrans that are described in literature, the colony was maintained in the Laboratório de Dípteros Hematófagos - UFRRJ. The bioassays were done in the Laboratório de Controle Microbiano de Atrópodes de Importância Veterinária - UFRRJ, using the strain 959 of M. anisopliae in a water suspension. In the first method, eggs were immersed in the suspension (2.2 × 108 conidia /ml and dilutions) and transferred to Petri plates with hydrophilic cotton. In the second methods (2.3 × 108 conidia/ml and dilutions), eggs were immersed and transferred to the larval rearding medium. In the third method (2.1 × 108 conidia/ml and dilutions), eggs were put in the larval rearding medium surface and one aliquot of fungus suspension were added. Larvae with nine days of development were immersed in suspension (2.1 × 108 conidia/ml and dilutions) and after that were transferred to the larval rearding medium while pupae with 16 days of development were immersed in suspension (2.3 × 108 conidia/ml and dilutions) and were held in Petri plates. Experiments were carried out with 107, 106 and 105 concentrations of conidia/ml and positive and negative controls. The mortality was assessed on the 10th day after fungus exposure. It was verified high mortality in all treated and control groups in the first method of eggs exposure. In the other two methods the eggs exposed to 108 conidia/ml concentration were 100% unviable. In the second method the eggs was 92.5% unviable and the third method was 53.33% both in 107 conidia/ml concentration. The subsequent concentrations did not show significant difference when compared to controls, neither between two methods of fungi exposure. Larvae and pupae exposure did not show statistic difference between treated and controls groups. Metarhizium anisopliae suspensions in high concentrations were capable to make unfeasible eggs of S. calcitrans; however, it did not happen in larvae and pupae experiments, in which fungi did not prevent their development. The second method was the best one to control immature forms of S. calcitrans but the third one resembles the nature conditions, in which has significant result only in the highest fungi concentration. Experimental methodologies that simulate nature conditions may optimize the utilization of fungi in arthropods control, in a way that it does not modify its action when applied in the field.