| The brown planthopper (BPH) Nilaparvata lugens Stal is an important rice insect pest that can cause serious damage to the rice production in China and Southeast Asia. Under the serious situation that BPH produced high resistance caused by pesticide misuse, it is necessary to find new biological control method to manage the pest. In this paper, several entomopathogenic fungi strains were tested in this experiment and one strain of Metarhizium anisopliae (Ma22) with higher virulence to BPH was selected. On the basis of bioassay, the time-dose-mortality model of Ma22 strain was established for its ability to affected BPH. In order to laid solid foundation for BPH fungi biocide manufacturing, we detected the biological compatibility of common pesticides with Ma22 and optimized the components of solid-state fermentation medium for Ma22 spore production. The primary results are as follows:1 The virulence of different fungi on Brown Planthopper, N. lugens12 strains of entomopathogenic fungi including Beauveria bassiana, B.brongniartii, M. anisopliae, M. flavoviride were chosen to the bioassay and the virulence to BPH were determined. The results show that the pathogenesis effects of fungi to BPH were significant difference between strains. One of the M. anisopliae strain Ma22 has the highest virulence to BPH, when BPH were infected after five and nine days, the cumulative mortality was 23.76% and 65.42%, respectively, significantly higher than other treatments. Regression equation and half lethal time (LT50) of each treatment were calculated from the bioassay data. LT50 of Ma22 strain was 5.64d, faster than other treatments (9.22～16.66d). Combination of BPH mortality and LT50 data, Ma22 strain can be considered the highest virulence of BPH in all the tested fungi.2 The time-dose-mortality model of M. anisopliae Ma22 affected N. lugensTime-dose-mortality model was applied to evaluate the virulence of Ma22 against BPH. After infection, dead BPH first appeared in the 3rd day and peaked in 5th～6th day. The value of t-tests indicated that dose effects and time effects of Ma22 strain were significant. The estimate values of LC50 were between 5.04×1010～2.24×105 spores/ml from the 3rd to 8th day. With the increase of concentration of fungal conidia used in inoculation, LT50 estimate values of BPH decreased. When the concentrate was 1×106 and 1×107 spores/ml, LT50 estimate values were 5.38d and 4.52d, respectively. 3 Biological compatibility of M. anisopliae Ma22 with pesticidesUse spore germination rate and suppressing rate of mycelia growth of Ma22 as indicators, the compatibility of sub-lethal concentrations of pesticides with Ma22 isolate were evaluate. The results show that the inhibitory effect of three fungicides on Ma22 were very strong, suppressing rate of spores were all higher than 95% and inhibition of mycelia all higher than 70%. The inhibitory effect of insecticides on Ma22 were quiet different, abamectin and Bacillus thuringiensis(Bt) had poor compatibility with the fungus, By contrast, buprofezin, chlorpyrifos and imidacloprid were compatible with Ma22.Buprofezin, imidacloprid and chlorpyrifos were selected to detect its long-term compatibility with Ma22 spores. The results show that, at 4℃and 25℃, the three insecticides all had small influence on the fungal spores when they mixed together for 30 days storage. But long-term mixed storage (50-100d) showed insecticides are still poor compatible with fungus, a high proportion of fungi spores were killed by insecticides. In comparison, buprofezin has the best compatibility with Ma22 spores in the long-term storage.4 Components optimization of solid-state fermentation medium for Ma22 spore productionUsing quadratic general rotatable design method to discover the combination effect of experimental factors rice(X1), rice husk(X2) and Tenebrio molitor excrement(X3) with spore production, and mathematical regression model was established. Single-factor effects and two-factor interaction effects of experimental components on the spore production were simulated through computer. Using variable rotation method and statistical optimization, we get the best level coded value:X(X1, X2, X3)= X(1.682,1.682,0), the amount of rice is 1168g, rice husk is 133.64g, and Tenebrio molitor excrement is 80g.
|
PDF Full Text Request