Preliminary Study On Epidemiology Of Metarrhizium Anisopliae Disease Of Grasshopper

Epidemiology of Metarrhizium anisopliae was made in the Duolun Caimu Mountain Reservation Area in Inner Mongolian.There are 18 grasshopper species belonging to 7 subfamilies including Arcypteridae,Oedipodidae,Catantopidae,Gomphoceridae,Acrididae,Pamphagidae and Tetrigidae were recorded in the experiment area.The characteristics of grasshopper population diversity in different habitat environment was analyzed and the result showed that the predominant species was Dasyhippusbarbipes(F.-W.)in the early occurrence period,Chorthippus albonemus Cheng et Tu in the middle and Chrothgppus fOIlax(zuboysky)in the late.The Shannon-Wiener index of degraded grassland was less than that of typical steppe and transitional type between meadow steppe type and typical steppe,In addition,desertification of grassland results in the decrease of grasshoppers diversity index and the amount of Oedipodidae and Pamphagidae with bigger appetite and bigger somatotype in degraded grassland was higher than that in others habitat environment.Mathematical models of population dynamic showed the amount of main populations were fluctuating in single peak,and different full incidence period of species resulted in the longest duration of high population density,Thus,the optimum control period should be before June 22 in current year.Results of cage experiment showed that affected grasshopper could spread disease of Metarrhizium anisopliae to health.When the proportion of affected and health grasshopper was 10:50,20:40, 30:30 and 40:20,the transmission rate between individuals within same species was 24.6%,31.0%, 39.0%and 52.0%respectively,while the transmission rate from species occurring early in the season to those occurring late was 15.6%,23.5%,32.7%and 40.0%respectively,and this maybe resulted from interspecific difference.Disease of Metarrhizium anisopliae can spread 400 meters far away from spraying area,and the average of infection rates from 8 directions around treatment area was 8.95%at 40 days after spraying, and the infection rate increased with time delaying.The level of infection rates from different directions was different,and it was the highest in northwest and southwest,east,north,south and northeast took second place,southeast and west were the lowest.The migratory tendency of grasshopper and wind direction may affect the spread of disease.Decrease of grasshopper population has been obtained with the spread of disease from spray area.At 200 metres distance to the treatment area,the average of corrected mortality from 8 directions was 44.05%at 42 days after spraying.The corrected mortality of different directions were different from each other,the level of corrected mortality keep consistent with infection rate in directions.Metarrhizium anisopliae oil was sprayed on band pattern,and the results showed that moving and feeding behavior of grasshopper could spread disease,an effective control was obtained in non-spraying insecticide area between sprayed bands.The spatial distribution of residual grasshoppers and cadavers after Metarhizium flavoviride oil spraying were analyzed by some indexes comprehensively in different sample interval and verified with Taylor's Power Law and improved Iwao's regression method during whole investigation period.The results showed that the spatial pattern of residual grasshoppers had the characteristics of regular aggregation and random distribution with the decrease of population density,and the cadavers were in aggregated pattern of distribution in different sample interval.The analysis of improved iwao's patchiness and Taylor's law showed that the spatial pattern of residual grasshoppers was aggregated within the whole investigation period which the cause was different reduced degree of densities in some plots after sprayed.Cadavers appeared to a false appearance of aggregative distribution with lower density and lesser sampling numbers.