Development Of A Wettable Powder Of Isaria Javanica For Control Of The Lesser Green Leafhopper

The lesser green tea leafhopper, Empoasca vitis, is one of the most important pest intea plantations throughout tea production provinces in China. It usually causes greateconomic loss due to its high fecundity in its annual multiple generations.In the present study, a highly productive and virulent isolate of Isaria javanica wasused to develop a wettable powder. Conidia were produced by routine biophasicfermentation with spore count at1×1011·g-1, germination at98.68±0.33%and watercontent at1.21±0.13%for formulation tests. They were mixed with some commonadjuvants for tests of compatability and physical-chemical properties. The first principlefor sieving adjuvants was the compatability to the conidia, i.e., they must affectgermination rate not significantly.5adjuvants were chosen in turn, Sepiolite was chosenfirstly as carrier from4inert carriers, which got wet3~5minutes soon after beingimmersed into water. Sepiolite and conidial powder were then mixed with12wettingagents for wetting agent sieving, resullting in A, which wetted in3seconds. Then sepiolite,A were mixed with conidia for dispersant sieving, resulting in B from7dispersants, withwhich suspension rate up to94.9%. By this method, fluorescein sodium was chosen forUV protectant from2protectants, with protection rate up to69.2%. In addition, C waschosen for antioxidant from2antioxidants according to Zhan’s study. The finalformulation was determined as follows: conidial powder (conidial content1011·g-1)10%,wetting agent A3%, dispersant B5%, fluorescein sodium1%, antioxidant C1%, withcarrier sepiolite added up to100%.A formulation was made by the above formula and was assessed for its quality. Theresult showed that various properties reached and exceeded partly state standard forwettable powder. The wettable powder and pue conidial powder were compred for theirpathogenicity through a bioassay. The result showed that the formulation was notsignificantly less virulent than pure conidial powder, with LT50at6.0days, as compared to5.9days by conidial powder.The wettable powder and the oil suspension with I. javanica developed also here weresprayed in a random block test at a dose of7.5×1013conidia×ha-1in April to May,2013..The leafhopper population was investigated daily. The result showed that the fieldefficacies of the2preparations were not significantly different. The wettable powdercaused the peak mortality of the hoppers at49.2%on the11th day, as compared to50.2%by the oil suspension. One spray is obviously not sufficient to suppress the increase of the hopper population, and a second spray is needed, suggesting that this biopesticide is onlysuitable for economic crops such as tea plantations with high added value.A storage test was run. The result showed that the viability of the unformulatedconidia declined to below50%at room temperature in summer after2months,significantly lower than those in the wettable powder (90.4%). In the7th month, theconidia in the pure conidial powder almost completely lost their viability, while those inthe wettable powder kept above50%, slightly lower than the conidia stored at4℃. Therewas no significant viability difference between the conidia in the wettable powder and inpure conidial powder at4℃. In late stage, the declining rate of the conidia in the wettablepowder was even slightly slower than that in the pure conidial powder. All these suggestthat the formulation developed is of application potential.