Research On Thermotolerance Of Beauveria Bassiana Against Western Flower Thrips And Development Of Wettable Powder Formulation

Western flower thrips, Frankliniella occidentalis(Pergande) is one of the most destructive pests worldwide, which threatens the crops production of our country. Western flower thrips can not only affect the appearance of crops by feeding the juice, but also transmit virus, the damage caused by virus is far more serious than by thrips. Biological control, especially entomogenous fungi for their innocuity to men and livestock and pollution-free to environment, plays a more and more important role. Beauveria bassiana was tested to have good control effect against western flower thrips. The pathogenicity of 191 isolates of Beauveria bassiana were tested against western flower thrips under laboratory conditions, and conidial production and thermotolerance of highly virulent isolates were tested, then thermotolerance of isolates were compared in each province. The strong thermotolerance isolates were further subcultured for five generations separately and then the conidia were exposed to thermal stress. The formulation of Beauveria bassiana wettable powder was developed under laboratory conditions, control efficacy was tested in field trials, shelf-life was tested in lab. The major results are listed as follows:191 isolates of Beauveria bassiana from different origins were tested for virulence against adult Frankliniella occidentalis, 61 isolates displayed highly virulence, and their LT50 values were less than 4.1 d, and conidial production of these 61 isolates were tested, the results showed that there was significant difference among them(F=31.88,P<0.01), 13 isolates had high conidial production,such as GZGY-2、JLGZL-9、SDDZ-2、JLGZL-14、SCWJ-2、XJWLMQ-32、SDDZ-20、HNLY-39 and so on. The maximum in sporulation of the best isolate HNLY-39(7.38 108 conidia/cm2), was15 times more than the worst HNLY-23(0.47 108 conidia/cm2), the mean value was 3.42 108 conidia/cm2. Isolates were classified high sporulation, medium sporulation and low sporulation.The conidial suspension of each screened isolate, was exposed to the thermal stress of 48°C in water bath. LT50, the time for 50% of conidia which lost viability under thermal stress was defined as thermotolerance index. The results showed that the median LT50 of 61 isolates were 34.28 min(6.94-53.67 min), and ten isolates were determined as high thermotolerance strains, which the LT50 values were longer than 45 min. These ten isolates were further subcultured for five generations separately, and then the conidia were exposed to thermal stress of 48 °C. As a result, thermotolerance of six isolates degenerated, only four isolates, XJWLMQ-49, XJWLMQ-32, JLGZL-14 and SCWJ-9 maintained stable, considering sporulation, XJWLMQ-32 and JLGZL-14 were with application potential. Indices of conidia harvested using liquid-solid dual-phase fermentation method showed that yield of conidial powder was 23.26 mg/g, quantity of conidia was 1.85 1011conidia/g, water content was 7.19 %, viability of conidia was more than 90%, which indicated that isolate XJWLMQ-32 was fit for expended production.Comparison of thermotolerance of isolates from eight provinces showed that thermotolerance presented ruleless among provinces, as each province had strong thermotolerance and weak thermotolerance strains, so screening should not be limited to the southern provinces.We screened the carriers, wetting agents, dispersing agents, and UV protectants, and successfully developed a wettable powder formulation, the formulation contained 30% conidia, 5%wetting agent A, 5%dispersing agent B, 1%dispersing agent C,0.5% UV protectant D, and kieselguhr. The indices of the wettable powder we developed were in accord with the GB, the germination rate was 94%, quantity of conidia was 4.5×1010 conidia/g, the wetting time was 17.33 s, the suspension rate was 72.45%, the water content was 3.67%, the p H value was 7.21, the fineness was more than 98% particle could pass through 325 mesh sieve.In order to test the field efficacy, we carried a field experiment in Langfang Test Base of plant protection institution of CAAS.After spraying WP(108conidia/m L) in greenhouse, the formulation produced no harm to shallots, and 10 days later, field efficacy against western flower thrips was more than 60%, which indicated that it had good control effect. Then the WP were stored at 4°C and room temperature, and indices were tested each month.When stored six months later, relative germination rate of WP stored at 4°C was more than 90%, and more than 80% if stored at room temperature.