| Based on understanding of control strategies on grasshopper all over the world, a new oil formulation of the entomopathogenic fungus, Metarhiziwn flavoviride, and its toxicity on different kind of locusts, control effects in natural condition and pathological processes of tissue cell of infected-locusts were studied. 1. Comparing stickiness and volatility of different mixing oils and their effects on germination of spores of M flczvoviride, a new oil formulation of M fiavoviride that be suit to control grasslands was screened. Mixing oils were from two plant oils and three mineral oils at different ratios. Peanut oil and kerosene that were mixed at 1:3 of mixing ratio were determined as appropriate substrate oil. Also, an ultraviolet radiation absorbefacient, UV-i, as protesting agent of oil formulation, was screened. 2. Toxicities of oil formulation of Metarhizium on different kind of grasshoppers were tested. The results indicated that toxicity on Oedaleus decorus asiaticus B-Bienko was significantly higher than toxicity on other tested-grasshopper species, medium ieathal concentration was only 8.75>< 102 spores/mi, all of adult died at different concentration in 10 day afier treatment. More than 90% of mortality rates of three tested locust species, Angaracris rhodopa F - W adult and A baraben.sis (Pall.) adult and the fourth-instar nymph of Locusta migra.toria ,nanilensis (Mey), were observed in 14 day after treatment at different concentrations. Toxicity of the oil formulation on 0. decorus asiaticzss ranked number one, A. rhodopa adult and A. barabensis ranked number two, L. migratoria manilen.sis ranked number three. Results of caged spot in semi-natural condition indicated that mortality of nymph population of 0. asiczticus was almost 99.28% 13 day after application with at a dose of 1.75 X 102 spores/mI of oil formulation. However, mortality of adult population sprayed at a dose of 1.25>( iO~ spores/mi was only 78.4% 14 day later. To control adult in fields, the proper concentration was 1.25>( I O spores/mi, to nymph of grasshoppers 1.75 X i0 spores/mi. The third-fourth instar nymph of grasshoppers was the most effective control period. 3. Grasshoppers in experimental area were controlled well in grassland in 1997-1998, by spraying the oil formulation. Sampling results in field showed control effect was 82.7% in 12 day after treatment, 89.7 1% of population reduced rate was still observed in field 37 days later. Grasshopper of high concentration treatment (5)< iO spores / ml) could be control well in short stage. With continuation of treatment, control effect of low concentration treatment (2.5 X 1 0~ spores/mi) was not significantly different with high concentration in long stage. So composition of mixing population of grasshoppers, population density, vegetation coverage degree and weather should be considered in choosing optimal control period on grasshoppers in fields. 4. Toxicity test and control effects in field were summarized, and then the pathological processes in tissue cells of infected-grasshopper were observed under electromicroscope. The results showed spores of Metarhizium germinated through body of locust at the end of 24 hours after treatment and then reproduced with hyphae body, nutrients in fat tissue cell of host were absorbed and formed many empty circles in late-stage and led to disintegration. Bao-dong Yang Entomology Supersor:Professor Kui-jun Zhao Fang-hao Wan...
|
PDF Full Text Request