Encapsulamento de linhagens de Bacillus thuringiensis do Maranhão para o controle de Aedes aegypti em condição simulada de campo

Abstract

Biological insecticides are being used as alternatives to control disease vector mosquitoes, including the Bacillus thuringiensis, an entomopathogen, capable of synthesizing toxic protein crystals during the sporulation process, called Cry and Cyt proteins. Currently, biopolymers are widely used for the encapsulation of bioinsecticides, which is an alternative to improving the persistence of products in the field. In the present work, the microencapsulation of two strains of the entomopathogenic bacterium Bacillus thuringiensis (BtMA-750 and BtMA-1114) was investigated, which act as highly toxic bioinsecticides for the mosquito vector Aedes aegypti. To this end, the encapsulation of different concentrations of microorganisms in starch microparticles was evaluated using the inverse suspension polymerization technique. It was possible to observe that greater quantities of bacteria caused a slight decrease in the diameter of the particles, ensuring that even the encapsulated bacteria still has an average diameter suitable for consumption by A. aegypti larvae. Furthermore, it was noted that the presence of both strains of B. thuringiensis did not affect the thermal stability of the particles. The microencapsulated bacterial strains demonstrated a high number of viable spores and preserved the expression of proteins with molecular masses corresponding to the insecticidal toxins Cry and Cyt, reinforcing that the encapsulation process was carried out in a controlled manner. Finally, the encapsulated strains were tested in the laboratory against A. aegypti larvae and maintained 100% larval mortality for 35 days. The BtMA-1114 encapsulate presented LC50 and LC90 with 0.0075 mg.L-1and 0.0872 mg.L-1, respectively. The BtMA-750 lineage presented higher values of LC50 with 0.137 mg/L and LC90 with 10.08 mg.L-1. In simulated field conditions, larval mortality was observed in containers exposed to sunlight during 23 days of experiment applying the LC50 of the encapsulated BtMA-750, whereas in the encapsulated BtMA-1114 high larval mortality was observed until the third week of bacterial exposure. Therefore, it was demonstrated that microencapsulation of B. thuringiensis with starch using the inverse suspension polymerization technique not only guarantees bacterial activity, but also prolongs the action of the bioinsecticide. Such discoveries highlight the great potential of new bioinsecticides, which can help reduce population rates of the mosquito vector A. aegypti in a sustainable way and without harming the environment.