[Evaluation for enhanced aphidicidal activity of a noval emulsifiable formulation of Beauveria bassiana conidia].

A noval emulsifiable formulation (EF) of Beauveria bassiana SG8702 containing 10(10) conidia/mL was prepared by suspending dry conidia in mineral oil-based liquid containing emulsifier, stabilizer and UV protectant (emulsion), and then bioassayed on newly merged adults of the green peach aphid, Myzus percisae, in parallel to the unformulated conidia (UC). For inoculation, five gradient concentrations of aqueous EF and UC suspensions (5 x 10(5) - 1 x 10(8) conidia/mL) were separately sprayed on to aphids on detached cabbage leaves (30 - 40 adults/leaf) using a Micro Ulva hand-held sprayer, generating EF dosages of 1.5, 6.3, 32.6, 87.6 and 701.1 conidia/mm2, and UC dosages of 2.8, 9.2, 52.7, 114.8 and 1005.9 conidia/mm2, respectively. All dosage treatments including controls for EF (100-fold dilution of the emulsion) and UC (water spray) were replicated three times (aphid colonies on three leaves), and maintained in Petri dishes at 23 degrees C and 12 : 12 (L: D) for 8-day daily records. Cadavers, whenever found, were moved into a moist chamber to facilitate fungal outgrowths for verification of B. bassiana infection. The resulting data fit very well to time-dose-mortality model with EF having a larger dose effect (1.05 +/- 0.10) than UC (0.82 +/- 0.11) and also faster time effect. The estimates of the dose- and time-effect parameters were then used to compute lethal concentrations (LC50) and time lengths (LT50). The estimates of LC50 with 95% confidence intervals for both EF and UC were 9.0 (6.9 - 11.6) and 634 (263 - 1532) conidia/mm2 on day 4 after spray, and 3.3 (2.4 - 4.6) and 5.3 (3.2 - 8.6) on day 7, apparently decreasing with increasing time lengths after spray. The estimates of LT50 for EF and UC were 4.9 d and 7.2 d at 5 conidia/mm2, 4.0 d and 5.6 d at 10 conidia/mm2, and 3.2 d and 4.5 d at 100 conidia/mm2, indicating a trend of decrease with increasing counts of conidia attached to the leaves. The results indicate that the emulsifiable formulation of B. bassiana conidia had greater aphidicidal activity than the unformulated conidia. Finally, problems with evaluation of mycoinsecticides and other microbial formulations are discussed and technical standards are recommended.