Identification Of A Pathogenic Strain Of Locusts And Its Toxicity And Pathology

Locusts disaster is the worldwide disaster. In recent years, frequency and severity of locusts disaster has been aggravated for some reasons such as weather change, seasonal distribution malajustment and increasing human's acvitivities. In our country, during the course of 90's, spread area of Locusta migratoria manilensis(Mey) added up to 1.2 hundred million mu. Especially in 2000, disaster led by Locusta migratoria manilensis(Mey) happened in 160 counties of 12 provinces, which area was over 30 million mu. According to experts' analysis, locusts disaster tends to aggravation gradually. Prevention and control of locusts disaster became an urgent task. At present, means to control locusts harm is chemical medicament which can reduce insect density. Chemical control had the advantage of speediness, high efficiency, flexible use etc. However, it leaded to a series of problems for example that drug-fast locusts came into being, efficiency of pesticide decreased, enviroment was polluted, rudimental toxicity remained and ecological balance was destroyed. Thus biocontrol technology emerge as the time require, and is increasingly regarded.A pathogen strain HR-3 was isolated from naturally dead grasshoppers, Locusts in 2-3 instar were repeatedly infected by HR-3, then appeared the alike symptom as above. The same pathogen was isolated from dead grasshoppers infected. Itspathogenicity was testified by law of KOCH. HR-3 grows well in common broth peptone culture medium at 28 °C. If 1% surcrose adds into it, HR-3 grows better. The pH range is 6.5-8.5. The growth quantity of HR-3 was measured by flora counting, and its growth curve was measured. The result was that the logarithmic phase of HR-3 was 4-28 h; the stationary phase was 28-48 hours after it was cultured. It was identified as Serratia marcescens by physiological, biochemical test. The molecular identification of HR-3 was performed. Through the comparative 16S rDNA sequences analysis, the 16S rDNA sequence of HR-3 had high homology with typical Serratia marcescens from the RDP library (between 99.2% to 99.3%), which confirmed the former result.Toxicity of HR-3 to grasshoppers was assayed by means of oral infection. Based on stat analysis software SPSS(Vll.O), 48h toxicity results show that the linear regression relationship between the logarithm(y) of HR-3 concentration and the probability (x) of corrected grasshopper morality is y= 1.067+0.809x, and the median lethal concentration is ZCso=1.164X 10 cfu/mL. Virulence mensuration results reveal that HR-3 has the obvious lethiferous effect on locusts. Locusts began to die after 24h, and reached peak value of death after 72h. The larvas act slowly and lumberly, as well as had no appetite. The infection mechanism of HR-3 to grasshoppers was also studied. The histopathological studies show that midgut epithelia are increased after 12h infection; After 24h infection, epithelia cells nucleolus condensed, dissolved, then partial denaturalization and putrescence occur in this area..After 48h infection, all epithelia cells are entirely denatured, vacuoles appear in most regions of midgut epithelia...