Comparative Ecology Study Of Three Entomogenous Fungi

In the present thesis,comparative ecology of Beauveria bassiana(Bb),Metarhizium anisopliae(Ma),Isaria farinose(If),two isolates of each,was studied in laboratory and in field,including impacts of temperature,humidity,UV on the viability of their conidia,and their resistance to soil antagonism,as well as survival of conidial powder and non-woven fabric sheets pregnant with Bb in forest and virulence change at different time during survival.The impact of temperature on viability of the conidia of the 6 isolates was studied with germination as an estimate.The result showed that the suitable temperature for Bb was 22℃～28℃for Bb,25℃～28℃for Ma,and 18℃～22℃for If.The half germination time(GT₅₀) of the 6 isolates showed that the general germination under different temperature was in the following order:Bb897＞Bb202＞Ma45＞Ma83＞If102＞If104.The comparison on the germination of the fungi under different temperature showed that the germination of all the isolates decreased as humidity declined;the germination of If was lower that those of Bb and Ma at 99%RH,while that was close to or even higher than those of the two fungi at 75%,suggesting that If was more tolerant to drought than Bb and Ma.The result of a germination test on the conidia of 5 isolates of each fungus irradiated with different UV revealed that the damage of UVb declined as wave length increased within its wave length range.A clustering analysis showed that the susceptibility to UVb was categorized into two types:all 5 isolates of Ma were very sensitive and got easily deactivated,while the 10 isolates of Bb and If were less sensitive,with not obvious interspecies difference.In the soil antagonism test,conidium germination of all the isolates rose when the concentration of sterilized soil was increased and declined when the concentration of non sterilized soil increased.The antagonism ability of the 6 isolates to soil microbes was in the following order:If104＜If102＜Ma45＜Bb897＜Ma83＜Bb202 at the concentration of 0.025g/ml,;in the following order:If104＜If102＜Ma45＜Ma83＜Bb897＜Bb202 at 0.05g/ml;and If102＜If104＜Ma45＜Bb897＜Ma83＜Bb202 at 0.075g/m.In general,If had the lowest antagonism ability,while Bb had slightly higher ability than Ma.In the field test,it was found that plot condition exerted obvious effect on the fungi surviving in the soil.In the soil on shade slope,general amount of the fungi was substantially large,with different surviving trends of the 3 fungi:Bb inocula rose twice in Mat to June and October to December,stagnated in December to February,and declined gradually in the other months;the conidial viability of Ma declined in a more obvious trend than Bb,declined quickly from the beginning and got stable from early September, with soil inocula at around 10³/g CFU's per gram soil;the soil inocula of If kept more stable than those of the other 2 fungi,with slight decline although general amount of the inocula declined gradually,and with 2 peaks after the treatment,especially the more obvious rise for October to December.The investigation on the of the survival of conidia on the conidia on the non-woven fabric sheets released in April revealed that the conidia survived differently under different conditions:the conidia maintained their viability substantially on the sheets in forest plots on shade slope with weak sun radiation,while those on the other plots declined obviously. The germination test on the fungi showed that germination of Bb kept high until August, while conidia of Ma lost their viability from the beginning of August,and germination of Is conidia declined in a stable and small rate.The bioassay results of the fungal conidia released in April and recovered at different time showed that virulence of all the 6 isolates changed poorly:virulence of 3 of them declined within just 4～35%,while that of Bb897 and Ma45 rose 4～39%,and only that of If104 declined for 134%;however,virulence of various isolates all declined to different degrees after July,and Ma83,Bb897 and Ma45 among them declined substantially,down by 11.35,10.69 and 7.66 times,respectively after one year.Bb 202 kept its virulence up to 6 months,although its virulence declined only by 1.68 times with the decline peak appearing late.Comparatively,the virulence of 2 If isolates declined to a slightest degree by only 0.55 and 0.76 time,respectively,and even rose back for a while 6 months after the release.