| Green peach aphid?Myzus persicae Sulzer?,belongs to Homoptera,Aphididae,infesting on various plants.Green peach aphid mainly infest on cruciferous vegetables such as cabbage,radish,mustard,rapeseed,etc.Green peach aphid has short life cycle and a large number of descendants.In addition to sucking plant sap,they also secrete honeydew and causes sooty,affecting the growth of plant and spreading a variety of plant viruses.This pest has the characteristics of fast propagation,wide distribution,and serious harm.This paper first selected 4 high virulent strains against greenhouse peach aphid through bioassay experiments,and then studied the effects of concentration,temperature and relative humidity on the pathogenicity of entomopathogenic strains.Re-isolated and purified strains from the infected corpses of aphids were prepared and bioassay was performed.Secondly,the pathogenicity of the highly virulent strain of Bb2488 against P.xylostella was studied.Finally,the green house control effects of B.bassiana Bb2488 and L.lecanii V07 against the green peach aphid were studied.The main results are stated as follows:Screening of highly virulent strains: using the methods of soaking insects to measure the virulence of 10 strains against the second instar larvae of green peach aphids.The results showed that: virulence order was: Bb2488> V07> Bb2032> Bb107,corrected mortality was 100%,97.06%,94.12%,88.24%;The LT50 was: 3.136 d,3.756 d,4.976 d,5.665 d.Three B.Bassiana strains with high virulenceand one L.lecanii were selected for further study.Effects of different concentrations on strain virulence: at 25?,with different concentrations of 1×108,1×107,1×106,1×105 spores/ml,respectively,the virulence of 4 strains against the second instar larvae of green peach aphids were studied.The results showed that the higher concentration of spore concentration,resulted the higher accumulation mortality rate,the lower concentration resulted lower cumulative mortality.The LC50 of the four strains of Bb2488,V07,Bb2032 and Bb107 were 2.162×105 spores/ml,5.183×105 spores/ml,6.968×105 spores/ml,7.258×105 spores/ml.Effects of different temperatures on the strain virulence: at 25?,the virulence of the four strains Bb2488,V07,Bb2032 and Bb107 were strong.At 30?,compared to 25?,the virulence decreased.At 15?,the virulent of the four strains were weak.As the temperature up or down,strain virulence also reduced,25? was the optimum temperature for virulence.Effects of different moisture conditions on the strain virulence: we studied the virulence of the four different strains against the green peach aphids at 97%,85%,75%,53% relative humidity.At 97% humidity,corrected mortalities of the strain Bb2488,V07,Bb2032,Bb107 were 100%,92.27%,84.62% and 76.92%;at 53% humidity,the corrected mortality of 4 strains were 46.14%,30.80%,30.80% and 23.07%,respectively.At the relative humidity of 97%,the four strains had the strongest virulence to M.persicae.The effects of Re-isolation and purification of virulence: the highly virulent strains Bb2488,V07,Bb2032,Bb107 were selected to carry out re-isolation and purification for one,three,and five times.The virulence of the re-isolated strains for three times possessed higher virulence then the re-isolated strains for one time.The virulence of the re-isolated strains for three times possessed almost the same virulence as the re-isolated strains for five times.Biological properties of the highly virulent strains: the morphology of strains Bb2488,V07,Bb2032,and Bb107 were in line with the features of B.bassiana and L.lecanii.Bb2488 has the highest sporulation and growth rate,and the sporulation of Bb107 was the least.The order of colony growth rate was Bb2488> V07> Bb2032> Bb107.Greenhouse control effects of the highly virulent strains: the results of greenhouse biological control showed that: the mixed suspension?107 bassiana spores / ml and 25% benzoylphenal mixture of urine III No.?had the best control effect on green peach aphid,and the relative control effect were 83.5%,followed by B.bassiana spore suspension and L.lecanii.?107 spores / ml?,the relative control effect were 65.9% and 71.4%. |
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