Improvement, Production And Field Efficacy Of Emulsifiable Conidia Suspensions Of Beauveria Bassiana For Aphid Control

The entomopathogenic fungus, Beauveria bassiana, is an important microbial agent for insect control, and has been developed into a variety of commercial formulations worldwide over the past decade. In China, intensive research on various aspects of the fungus has undergone for several decades but no formulation has been commercially registered at present. On a basis of previous work on an aphid-derived isolate (SG8702) of B. bassiana in our laboratory, the present study was attempted to improve techniques involved in production, storage, and formulation of B. bassiana conidia powder. It also included observations for time-specific infection rate of B. bassiana on Myzus persicae and field efficacy of two emulsifiable conidia suspensions for aphid control on cabbage.Time-specific infection rate of B. bassiana on M. persicae. A suspension (5xl06 conidia/mL) of B. bassiana SG8702 conidia was used to inoculate newly emerged apterous adults of M. persicae, on detached cabbage leaves in an attempt to measure time-specific infection rate of the fungal agent. The aphids attached with conidia were disinfected using 0.2% chlorothalonil solution at intervals of 8-56 h after inoculation and then maintained at 10 and 20癈 for daily observation. The number of aphids in each treatment (a specific time interval under each temperature) ranged from 63 to 128 with a total of 1636 aphids being examined in all treatments including controls. There was a significant difference (P<0.05) in mortality attributed to the fungal infection among the time intervals within 56 h at 10癈 or within 40 h at 20癈 after inoculation. In comparison with the control (not treated with 0.2% chlorothalonil), time-specific infection rate at 10癈 was estimated as 22.9%, 48.8%, 64.9%, 80.4%, 72.7%, and 98.3% within 8 h, 16 h, 24 h, 32 h, 40 h, and 56 h after inoculation, respectively. The same estimates at 20癈 were 31.6%, 48.8%, 58.6%, 86.9%, 97.2%, and 98.7%, respectively. The results indicate that the first 24-h period after inoculation was crucial to the infection of B. bassiana to M. persicae. During this period, effective infection accumulated to 59-65% at 10-20癈. This finding supports the use of B. bassiana SG8702 for aphid control.Optional components for emulsifiable suspensions of conidia. In order to improve an emulsifiable formulation of B. bassiana SG8702 conidia previously developed for practical application, numerous components including oil-based solvents and emulsifiers were tested forbiological compatibility to the conidia. Pure conidia powder was added at 10% (w/v) to each solvent containing 0.1-10% of an emulsification called 'OP' (C34H62O2I) and then preserved at ambient temperature. The viability of the conidia was examined using samples from each combination of solvent and emulsifier during the storage. Based on estimates of conidia viability during a 270-day period of storage, a combination of solvent 'H' and 1% OP was found most compatible to B. bassiana conidia and could be used as primary components of emulsifiable conidia suspensions for formulation. The other components selected previously included the use of 0.3% CM-Na (sodium carboxymethyl cellulose) as a suspension stabilizer, 0.1% vitamin C as a desirable UV-protectant, and 1% of 10% imidacloprid WP as a synergic agent.Production of pure powder of U. bassiana SG8702 conidia. Conventional diphasic fermentation technology was used to produce pure powder of B. bassiana SG8702 conidia in a workshop. It was found during submerged fermentation that mycelial biomass in liquid culture fluctuated inversely to pH but well in accordance to pOH (=14-pH), indicating the pOH is a useful index for monitoring the yield of mycelial biomass. The 42-h liquid culture was then transferred at a ratio of 1:1.5 to a mixture of 40% wheat bran and 60% rice chaff in trays for solid fermentation for conidiation. Maintained at 24-26癈 and ?5% RH for 10 d and then dried at 30-35癈 for 3 d, 4 kg of conidia powder was harvested from the mixtures using a harvest machine. The powder contained 7.