MICROENCAPSULATION OF Bacillus thuringiensis (BERLINER) IN BIOPOLYMERIC MATRICES USING SPRAY-DRYING TO CONTROL Hyphantria cunea (DRURY)

Abstract

Background. The formulation of agents of biological origin with insecticidal activity is one of the most effective methods for the control of lepidopteran pests due to their feeding forms. The insecticidal activity of B. thuringensis is widely known, which is why it is believed that native strains of this bacillus could have toxic activity on larvae of the cobweb worm, H. cunea. Objective. To prepare by means of the spray drying technique microencapsulated formulations of a native strain of B. thuringensis with toxic activity on H. cunea. Methodology. The experimental design was completely randomized and the means were compared with the Tukey test (p ≤ 0.05). The strain selected for the formulation is a key Mexican strain GM-10 belonging to the aizawai variety and presented an LC50 of 0.007 ng cm-2 in artificial diet, and a LT50 of 80.83 h. To prepare the formulations, a phago-stimulant was first selected by means of food preference tests with powdered leaves of walnut, blackberry, ash, loquat and walnut shell powder and a commercial phage-stimulant (Coax®), and ash was selected with 61.4% of the larvae attracted. Once the phagostimulant was selected, encapsulated formulations were developed with a mixture of polymers (Capsul®-bovine gelatin), as a base. Several formulations were then made to select an adhesion additive, and the ingredients tested were guar gum, core® gum and xanthan gum. Results. Food preference bioassays to establish the affinity of H. cunea for some of the formulations showed that the larvae had a similar affinity for feeding on all formulations (p ≥ 0.05), while in the trials to select an adherent for the formulation xanthan gum presented the best adherence (p ≤ 0.05). Implications. The evaluated formulations preserved their toxic activity after microencapsulation with an LC50 of less than 0.05 ng cm-2 of B. thuringensis. Conclusion. These results show the feasibility of using the spray drying method to obtain an effective formulation for the treatment of the immature stages of H. cunea.