Microencapsulation: A Strategy for Formulation of Inoculum

Abstract

A non-toxic phase separation method was developed for microencapsulation of inoculum used in biological control. Aqueous sodium alginate or gelatin and agar was mixed with inocula of various biopesticides and emulsified in a mixture of corn oil, n-hexadecane, and lecithin. Gelatin and agar globules gelled in the emulsion; alginate globules gelled after settling into a lower phase of aqueous CaCl2. A layer of gelatinous material thus surrounded the inoculum as 'capsules'. Mixing with n-hexadecane reduced the specific gravity and surface tension of the oil, allowing aqueous extraction of the capsules. Successful extraction of alginate capsules depended upon lecithin (>0.17%), n-hexadecane (>30%), and CaCl2 (>0.01 M) concentrations. Alginate-encapsulated macroconidia of Fusarium avenaceum caused 23±3% leaf area damage to seedlings of marsh reed grass, versus 4±3% for unformulated controls. In green foxtail seedlings, gelatin and agar-encapsulated conidia of Bipolaris sorokiniana caused 21.3 vs. 7.9 lesions per plant for encapsulated versus unformulated conidia. Mortality of Douglas-fir tussock moth larvae caused by a nuclear polyhedrosis virus was delayed when 23 polyhedral inclusion bodies (PIB) were incorporated into alginate capsules, but it proceeded normally for 2.3 PIB/capsule, where efficacy was also higher versus positive controls. Microencapsulation enhances the activity of biological control agents and protects them from adverse conditions.