| Fungal insecticides are developed with living conidia of Beauveria bassiana, poorly resistent to UV light, and are soon inactivated outdoors by environmental stresses. Various formulations should be developed towards different target insects to enhance their shelf life, raise their stress resistence, increase their easiness for field operation, and elongate their survival. Microcapsule formulation is characterized by substantial protection of core material against environmental from environmental influence, can increase storage stability and extend field persistence. They are suitable for the application in high value crops cost for their preparation is comparatively high. In the present study, a micocapsule of B. bassiana, was developed with the lesser tea leafhopper, Empoasca flavescens, as the target pest, based on the selected isolate of B. bassiana.1. Isolate screening and production of conidia powder Biological characters, extracellular proteinase level and virulence of 10 isolates of B. bassiana from various leafhoppers and tree hoppers were studied and Bb2151, a fast growing, fertillely sporulating, and highly virulent isolate from a tree hopper was selected as the candidate for microcapsule development study. Biphasic culture was made with the isolate, resulting in conidial powder with spore content at 1.7×1011/g, spore vitality at 91.87%, and water content at 3%.2. Screening of the material for microcapsule wall Through a germination test of the conidia premixed with 10 different macromolecular materials respectively for 6h and for a whole year, some well compatible materials were selected, in an order of pre-screened plastic starch, gelatin and methyl cellulose sodium, followed by Arabic gum, alginate jelly, and carboxymethyl cellulose sodium.3. Processing technique of microcapsulation Methods for preparation of microcapsule of B. bassiana were compared, including single phase separation- coacervation, double phase separation-coacervation, and coagulation bath. The result showed that all the specificities, including inwrap rate, average diameter and storage stability, were better by double phase separation-coacervation than by the other methods. By this method, all the specificities including inwrap rate, average diameter, storage stability and UV resistence of the microcapsules made of geletin-Arabic gum were superior to those made of geletin-alginate jelly, geletin-carboxymethyl cellulose sodium.4. Field efficacy of the microcapsulate formulation The microcapsule preparation based on geletin-Arabic gum as wall material was diluted into different concentrations and sprayed onto tea foliage. The population of the lesser tea hopper was suppressed to different extent. Among the treatments, the 500-fold suspension (2×107conidia/ml) resulted in the highest efficacy up to 78.58% after 21d, followed by the 1000-fold suspension (1×107conidia/ml) up to 78.57%, while the 1500-fold one (6×106conidia/ml) in the poorest efficacy at only 53.64%. Consequently, the concentration of 500- to 1000-fold of the present microcapsule formulation is recommended for the leafhopper control in tea plantations.5. Preparation technology and product specificities Through an integrated evaluation, an optimal preparation technology was determined for the water suspension of microcapsule of B. bassiana by the double phase separation- coacervation method, with system temperature at 35℃, stirring speed at 200r/min. The formula for the water suspension formulation is conidial powder 2% (w/v), geletin 3%, Arabic gum 3%. The specificities of the product was in-wrap rate at 81.5%±3.41%, average capsule diameter at 11.6±1.3μm, average conidium nember at3.25±.0.35. The water suspension was absorbed with kaolin (mesh 500) and dried 12h to make wettable powder of microcapsules, with specificies sporulation containing≥5×109/g, water content≤10%, fineness (over 50μm sieve)≥85%.
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