The Biological Character And The Pathogenic Mechanism On Myzus Persicae Of Zoophthora Radicans

The resources of Entomophthorales species in some regions of Gansu province were investigated, and Zoophthora radicans (Zryzh) that higher invasiveness on Myzus persicae was screened out , moreover, the biological character, virulence, pathogenic mechanism to Myzus persicae and the compatibility with pesticides of it were studied detailly. The results were as follows: 1. Based on the investigation of Entomophthorales, in seven regions of Gansu province,such as Tianshui,Lanzhou,Yuzhong,Tianzhu,Yongjing etc.These 8 species,which belong to three families and five genus respectively were among them ,two species had great pathogenic mechanism on the aphids , two species could infest Tetranychus urticae.The characters of identification,the range of the hosts,the areas and the methods of culture on these species were described detailly. 2. Bioassay of the 8 Entomophthorales against Myzus persicae were studied, Zryzh which had stronger virulence to Myzus persicae was screened (the mortality was 40.23% under the dosages that was 80.06×103 conidia /mm2), and its biological character was researched systemically. The optimum condition for the conidia germination was RH=100% and T=20℃. The optimum temperature for growth and spore production was 20℃.The acidity and alkalinity also affected the fungi, the range of pH for spores germination was 7.0~10.0, and that for the growth and spores producing was 7.0~9.0.The ultraviolet ray had great killness to the spores. In addition alternationg of light and dark could promote growth and spores producing. 3. The invasiveness and development process of Zryzh to the Myzus persicae was researched with pereffin wax microtome technology.The spores first land on the surface of Myzus persicae,after 20~24h, they germinated on the suitable conditions,and invased completely in 36h. The fungus multiplied with protoplasts in the host, then hyphal body broke through the host cuticle, the conidiophore peduncle produced the spores that began to intrude other host insects. 4. The virulence of Zryzh against Myzus persicae (1-2 instar nymphs) was tested with "spore shower"(20℃,12L/12D).The fastigium of Myzus persicae mortality appeared from third day to fifths day and the cumulative mortality of that were 16.19%~82.69% with the different spore dosage . Through the analysis of a time-dose-mortality model, the LD50 values estimated were 263.03,128.82,91.20,75.86 spores/mm2 ,respectively ,3~6d after inoculation. Thus, the Z .radicans isolate tested is of great virulence to M.persicae. 5. The compatibility between pesticides and entomomycete was researched, which provide scientific basis for applying rationally pesticides during the prevalence of entomomycete, and the influence of 23 pesticides against the colony growth and spore production of Zoophthora radicans with growth rate and Petri dish counting methods.The results showed that the fungicides had great effect on the growth and spore production of Zryzh, moreover, the infection of the insecticides and herbicides to Zoophthora radicans was different with the different kinds. Among 10 insecticides, inhibition rates of 5 insecticides were more than 60%, and that of decis and acetamiprid were smaller; the effect of dichlorvos against the was the highest and that of acetamiprid was lowest.Among the 6 fungicides, the other five fungicides had great inhibiting effect except for propamocarb hydrochloride. Among 7 herbicides, the largest inhibition rate was 79.84% when the herbicides was haloxyfop-r –methyl, while the lowest was 14.25% when the herbicide was tribenuron-methyl; spores production was tested, the maximum of spores production of colonies was 14.27×103 spores/mm2 that treated with tribenuron-methyl ,however the spores production of colonies that treated with others herbicides were smaller.