Encapsulamento de conídios de Metarhizium anisopliae: avaliação da estabilidade e potencial no controle de Rhipicephalus microplus

Abstract

Due to the problems generated by the indiscriminate use of chemical acaricides to control ticks, alternative methods have been developed, such as the use of entomopathogenic fungi. However, these entomopathogens have their viability compromised when applied under natural conditions, being indispensable the development of formulations. In this context, microencapsulation technologies for biocontrol agents are promising; since it provides protection against environmental factors as well as increased the encapsulated microorganism shelf life. Ionic gelation is a simple and financially viable technique when employed for the entomopathogenic fungi encapsulation. Thus, the aim of the present study was encapsulate the Metarhizium anisopliae conidia (LCM S01) in 2 and 3% sodium alginate, using the ionic gelation technique and, evaluate the external morphology, concentration, viability, shelf life, tolerance of UV-B irradiation, thermotolerance and efficacy of these microparticles in the control of Rhipicephalus microplus engorged females. The external morphology was characterized by ScanningElectron Microscopy (SEM) and the encapsulated conidia (EC) viability was determined by the germination percentage. For shelf life, conidia encapsulated in 2 (EC 2%) or 3% (EC 3%) of sodium alginate and unencapsulated (NEC) were stored for 1, 3, 5, 7, 9 and 11 months at room temperature and in a freezer. For UV-B tolerance assay, EC and NEC were exposed to 6.0 or 8.0 kJ m-2, while for thermotolerance, they were submitted to 42 ºC in a water bath for 2, 4 and 6 hours. Furthermore, the biological parameters of engorged females exposed to 30, 60 or 90 mg of microparticles under laboratory conditions wereevaluated. 2 and 3% sodium alginate fungal particles were spherical with a more homogeneous and heterogeneous surface, respectively. Encapsulation did not cause severe conidia losses and did not affect their viability. Encapsulation increased the conidia shelf life stored at room temperature for 1, 3 and 5 months compared to NEC. In the freezer, NEC germinated more than EC. The EC and NEC showed greater viability in the freezer when compared to room temperature. Heat exposure for 6 hours reduced the NEC germination compared to EC 2 and 3%. Different UV-B doses exposure also significantly reduced the NEC germination compared to EC. The particles were able to reduce significantly the engorged females’ biological parameters when compared to NEC and the control group, however, there was no significant difference between the particles evaluated. In general, no significant differences were observed between the sodium alginate concentrations used. Thus, the formulations developed in the present study increased M. anisopliae (LCM S01) shelf life, thermotolerance and UV-B tolerance, and were effective in R. microplus engorged females control, showing promising potential to control this tick.