| Most of the studies were conducted on multiple fungal strains by targeting a single insect.No much literature was found to control multiple insects with a single fungal strain.Therefore a study was designed to investigate the pathogenicity of entomopathogenic fungal strains against multiple plant sap sucking insects to find out some meaningful findings which not only will be helpful in insect control but also provide a safe free pollution environment,reduce the residual effect of chemicals that were used for the controlling of insects in agricultural,horticulture and in forest protection strategies.The application of different natural enemies with high control potential either by direct feeding or causing diseases by infecting their host is helpful to keep the pest population below the economic injury level without any adverse effect on non-target insect species and on the natural environment as well.In this case,Entomopathogenic fungi can fill the gap and can be considered a valuable asset to the current era of biological control measures.（1）In this study newly collected fungal species（Isaria fumosorosea strain Ifu13a and Beauveria bassiana Bb202）were obtained from the Provincial Key Laboratory of Microbial Control,Anhui Agricultural University,Hefei,China aim to study their control potential on different plant sap-sucking insects such as Jacobiasca formosana Paoli（Hemiptera:Cicadellidae）;Aphididae（Hemiptera）;Bemisia tabaci Gennadius（Hemiptera:Aleyrodidae）and on Stephanitis nashi Esaki et Takeya（Hemiptera:Tingidae）.The initial experiment was done in the laboratory for the screening of fungal isolate at the environmental condition of 21±1°C temperature and 78±5%relative humidity.The recorded results showed that both fungal species had excellent potential to control the target insects.The fungus Ifu13a strain showed mortality rate ranged from 81to 100%in the concentration of 1 x 108 conidia/ml.However,the lowest mortality of 33%was observed in the concentration of 1 x 105 conidia/ml against the S.nashi population.Median lethal times（LT50）were obtained from a regression-probit value which indicated4.1,4.1,4.8 and 7.3 days at a concentration of 1 x 108conidia/ml,whereas,median lethal concentration dosages（LC50）were calculated as 3.9×103,6.8×104,3.0×104 and 6.9×105conidia/ml against J.formosana,A.gossypii,B.tabaci and S.nashi,respectively.（2）When the insect species,Myzus persicae Sulzer（Hemiptera:Aphididae）,J.formosana.,B.tabaci.and S.nashi were exposed to conidia of B.bassiana at 1.0x102,3.5x103,5x104and 6.75x105conidia/mm2 to determine the pathogenicity of B.bassiana strain Bb202.The fungal strain Bb-202 showed the highest pathogenicity to the M.persicae and 100%corrected mortality observed in the treatments over 1.0x102conidia/mm2,followed by the J.formosana with a final corrected mortality of 86.6,94.4,and 97.4%after 10 days of fungal inoculation of 3.5x103,5x104,6.75x105conidia/mm2,respectively.The strain Bb-202 also showed good pathogenicity on the B.tabaci,and corrected mortalities of 77.9and 81.1%were recorded when exposed to 5x104 and 6.75x105conidia/mm2.Relatively weak pathogenicity was observed in the S.nashi,in which the highest corrected mortality of 63.7%appeared in 6.75x105conidia/mm2.Accordingly,the LC50 and LT50values of concentrations 1x105,1x106,1x107,1x108conidia ml-1 were calculated for the M.persicae,J.formosana,B.tabaci and S.nashi that was determined as 6.7x104,1.3x106,3.6x106 and1.2x107 conidia ml-1and LT50 was observed as 5.2～8.24,5.1～6.6,7.2～9.0 and 7.9～9.6in days,respectively.（3）The aphid species,crape myrtle aphid Tinocallis kahawaluokalani Kirkaldy,spiraea aphid Aphis citricola van der Goot and aphid A.gossypii were exposed to conidia of I.fumosorosea Wize strain Ifu13a at concentration levels of 1×105,1×106,1×107 and 1×108 conidia/ml under laboratory conditions.This was noticed that fungus was highly pathogenic to A.gossypii,and a corrected mortality of 67.9%was recorded at the concentration of 1×105 conidia/ml,while 100%corrected mortality was recorded at concentrations over 1×105 conidia/ml.Corrected mortalities of 21.6%and 34.6%were observed at a concentration of 1×105conidia/ml for T.kahawaluokalani and A.citricola,respectively,and the corrected mortalities increased to 86.4%for T.kahawaluokalani and61.8%for A.citricola at a concentration of 1×108 conidia/ml.LC50 values of 6.8×104,2.0×106 and 5.6×106,as well as the lowest LT50 values of 4.1,6.4 and 7.9 days,were calculated for A.gossypii,T.kahawaluokalani and A.citricola,respectively.（4）In order to investigate the effect of low relatively humidity on pathogenicity of both fungal species,an experimental trial was conducted in the glasshouse under the environmental condition of the mean 23 oC temperature and mean 47.5%relative humidity.The target insect B.tabaci was cultured on cucumber plants in the glasshouse and a single application dose of both fungal conidial rate of 1x107 was applied on B.tabaci population.The final 90%corrected decline percentage was recorded in B.bassiana treatment while63.3%decline percentage was observed in I.fumosorosea treatment after 18 days of application of fungal conidia.（5）Similarly,a field trial was conducted in the open field to determine the pathogenicity of both isolates on target insect A.gossypii.The trial was arranged in the month of September2017,under the humid and cloudy weather conditions with a 78%relative humidity and27.3 oC temperature.This field trial revealed that both fungal species showed a good pathogenicity to the target insect and a population reduction rate of 95%and 91%percentage was noticed in I.fumosorosea and in B.bassiana treatment respectively on the6th day after application of fungal suspension.The good field control indicated the entomopathogenic fungi could induce an epizootic of fungal disease in the target insect host’s population and pose an efficient control under a suitable environmental condition.Analysing all the results of laboratory experiments and field trials,this was observed 1)the fungal disease was density-dependent that higher fungal conidial density proved a rapid control,but the phenomenon of dosage-saturation or dosage attenuation was found in some fungal infection.2)The fungal strains showed host-specificity to different insect hosts,but the host-specificity was not related to phylogenetic relationship among them.3)Relative humidity played a key role in fungal infection,and a relatively high RH ensured a successful field control of target insects by the tested fungal strain.4)Initial infection is the most critical stage of causing an epizootic disease in insect population,once fungi built an infection among the insect it can sharply kill their host.5)The strain Bb202 showed a wide range of adaptability with environmental conditions as compared with strain Ifu13a when they were applied in the glasshouse at low relative humidity.However strain Ifu13a can be used as biological control agent under high relative humidity at favorable conditions... |
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