Study On Diphasic Fermentation Of Isaria Fumosorosea And Control Potential To Piercing-sucking Mouthpart Pests

Piercing-sucking mouthpart pests are important pests in agriculture and forestry.These pests are often with high reproductivity,multiple generations,easy resurgence,chemical resistance,and wide distribution.Invading insect hosts directly through their integument makes entomopathogenic fungi able to control sucking insect pests as an alternative of chemical insecticides.In this paper,an entomopathogenic fungal strain Isaria fumosorosea Ifu-13-a was selected in previous study from the fungal bank of Provincial Key Laboratory of Microbial Control,Anhui Agricultural University.Fermentation techniques of the fungus were studied both in liquid and solid media.Biomass and fungal growth were monitored every8 hours in the liquid fermentation by periodic sampling.The results showed the fungal biomass of the liquid fermentation in SDY medium at 25°C peaked at the 104th hour,and then decreased gradually.The morphological observation verified that long mycelia with clear cell wall and a large number of blastospores appeared in the liquid medium at 104hours fermentation.So the optimal time for the liquid fermentation of the fungus is 104hours,and fermented liquid at this time can be used in the subsequent solid fermentation as liquid seed.In the research of solid fermentation process,the optimum medium formulation was selected through canned bottle fermentation in the early stage.An optimal basic solid medium containing 11%wheat bran and 76%cotton seed hull produced the largest amount of 2.15×10⁹ spores/g.In the subsequent shallow tray fermentation technique,another factory-used solid medium from Jiangxi Tianren Ecological Enterprise was used as the compare.The results of solid fermentation showed the optimal solid medium was superior to the factory-used medium on conidia production efficiency.The optimal solid medium increased production efficiency by 21.8%in terms of cultural area.In addition,the thickness of the solid media greatly influenced the material temperature inside the fermenting solid media.The different thickness of the same solid medium（2 cm vs.4 cm）resulted in different fermentation temperature curves.The fermentation temperature of the4cm stack of solid medium was 5-6℃higher than that of the 2cm stack at the environment temperature of 18℃.Pathogenicity of the strain Ifu-13-a of I.fumosorosea against multipal sap-sucking insect pests,but there were still more obvious host specializations.The fungal strain Ifu-13-a showed high pathogenicity on T.vaporariorum,A.gossypii,and J.Formosana,and their cumulative mortalities reached 100%at an inoculated concentration of 1.0×10⁶spores/ml.The half lethal time(LT₅₀)of the 3 target insect pests were between 4-5 days.However,S.nashi,A.citricola and T.Kahawaluokalani,their mortalities were 81.25%,61.4%,and 86.36%at the concentration of 1.0×10⁸ spores/ml.The LT₅₀ were between 6-8days.An experimental trial was carried out in a greenhouse,in which the air relative humidity was low.An application dosage of 1.0×10⁷ spores/ml was used to control two target pest insects,T.vaporariorum and A.gossypii by ultro-low-volume spray.The aphid population in the control significantly increased from an initial population density of 40individual/plant to 118 individual/plant by the end of the 13 days experiment.On the contrary,the aphid population density in the fungal treatment decreased from 40individual/plant to 36 individual/plant,with a corrected control efficiency of 46.39%.Compared with the aphid Aphis gossypii,the control of T.vaporariorum by the fungal strain showed a higher control efficiency.The white fly population decreased from 150individual/plant to 36 individual/plant in 4 days,and then fluctuated within a certain range.At the end of the 13 days experiment,the whitefly population density was 78individual/plant,and the corrected control efficiency was 92.86%.The strain Ifu-13-a was sprayed to control cotton aphid at a concentration of 1.0×10⁷ spores/ml in a field experiment with relatively high relative humidity.The population of Aphis gossypii was reduced at the 10th day.Corrected control effects reached 96.2%and95.9%,respectively,demonstrating excellent field control effects.The different control effects of the greenhouse experiment and field trial further confirmed that the environmental humidity is a key factor influencing the fungal infection process and its control efficiency.The laboratory bioassay and field trails verified high virulence of the Ifu-13-a strain against a variety of sucking insect pests.The fungal strain Ifu-13-a is suitable to be developed as an biological insecticide and pose wider application on the prevention and control of many pests such as white flies,leafhoppers and aphids.