| Nilaparvata lugens is one of the most important rice migratory pests and has showed high level of resistance to many chemical insecticides.In order to evaluate the potential of entomopathogenic fungi to control N.lugens,Isaria javanica was screened as high virulence entomopathogenic fungi to this pest in this paper.At the same time,sensitive instar,median lethal concentration(LC50)and the enzyme activities in nymph infected by I.javanica were analyzed to evaluate the effect of I.javanica on N.lugens nymph.The oviposition of this adult and effect of I.javanica on insect reproductive system were also evaluated to show the effect of N.lugens reproduction by I.javanica.All the experiments were performed as follows:（1）Screening high virulence entomopathogenic fungi against N.lugens.The conidial suspensions of I.fumosorosea,I.javanica,Metarhizium anisopliae and M.anisopliae UV mutant were used to infect fifth instar of N.lugens,respectively,the result showed that the mortalities of insect was higher in I.javanica treatment with value of 21.8%as compared to I.fumosorosea treatment（19.9%）,Metarhizium anisopliae treatment（14.6%）and M.anisopliae UV mutant treatment（19.6%）.Both the spore harvested from I.javanica and M.anisopliae germinated on rice leaf and stem,the spore germination rate of I.javanica（more than 80%at 19 d）was higher than that of M.anisopliae UV mutant spore（less than 50%at 19 d）when cultured in rice leaf and stem juice,respectively.The conidial germination rates of I.javanica post 12 h cultured were 94.8%,98.6%and 99.6%when culture medium containing insecticide of Thiamethoxam,Dinotefuran and Pymetrozine with the concentration used in field,respectively.In summer and autumn,the survival of I.javanica conidia was observed on rice stem post 13-17 d treatment and on rice leaf after 13-15 d treatment,similar to M.anisopliae UV mutant with 17-19 d survived on rice stem and19-25 d survived on rice leaf.（2）Bioassay of N.lugens nymph against I.javanica.Both second and forth instars of N.lugens nymphs were susceptible to I.javanica than other nymph.The result showed that the mortalities of the 2,3,4,5 instar of N.lugens nymph were67.1%,42.6%,45.6%and 21.8%,respectively,after treated by I.javanica with the concentrations of 1×107 conidia/ml.The median lethal concentration of I.javanica against the forth instar of N.lugens nymph was 1.1×1013conidia/ml,in 5 d,with regrssion equation:Y=3.3638+0.1254X.The median lethal concentration of I.javanica against the forth instar of N.lugens nymph was 3.4×107conidia/ml,in 9 d,with regrssion equation:Y=3.4640+0.2040X.（3）Effect of Isaria javanica on 4 enzyme activities in Nilaparvata lugens nymph.The superoxide（SOD）,phenoloxidase（PO）,catalase（CAT）,perioxidase（POD）activities of N.lugens nymph were tested after the the forth instar nymph infected by I.javanica.The activities of four insect enzymes were increased with time pass on and then decreased during the time course of insect nymph infected by I.javanica,reaching peak values at 36～48 h post infection.In 1x108 concentration of fungal treatment,the highest values of SOD,PO,POD,CAT activity were 485.6U/mg,230.7 U/（g*min）,1181.6 U/（g*min）,657.7 U/（g*min）,respectively.（4）Effect of Isaria javanica on Nilaparvata lugens reproduction.The effect of I.javanica on N.lugens reproduction was evaluated by infecting the forth instar N.lugens nymph with I.javanica.Results indicated that the accumulated egg production of N.lugens adult emergence from the forth instar nymph infected by I.javanica decreased significantly as compared to that of the insect treated with no fungi,with accumulated egg production decrease 44.6% and 80.6% at the concentration of1×105 conidia/ml and 1×108 conidia/ml treatments post 29 d treatment,respectively.The average egg production per day of N.lugens adult emergence from the forth instar nymph infected by I.javanica decreased sharply after 6 d treatment as compared to that of control.And the average egg production per day of N.lugens adult at the concentration of 1×108 conidia/ml treatment decreased significantly as compared to that of the insect at the concentration of 1×105 conidia/ml treatment and the insect treated with no fungi.The survival rate of N.lugens adult emergence from the forth instar nymph infected by I.javanica decreased sharply as compared to that of the insect treated with no fungi,and the survival rate of N.lugens adult from the concentration of 1×108conidia/ml fungal treatment was lower than that from 1×105 conidia/ml treatment.The reproductive system of new emergence adult was damaged when the forth instar N.lugens nymph infected by I.javanica,with the number of ovarian ducts decrease of 6.5-11.5%in 1×105 conidia/ml fungal treatment.After inoculating the I.javanica spores,mycelium intruded into the isolated ovary and eggs,and then covered the ovary and ovarian ducts,deformed the ovary.There was significant effect on insect sex ratio of N.lugens adult emergence from the forth instar nymph infected by the concentration of 1×105 conidia/ml I.javanica,and with no effect on the rate of wing dimorphism. |
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