| Isaria fumosorosea, one of the most important entomopathogenic fungi, is a widely distributed fungus in the world and has a strong ecological adaptability. It showed a good potential to infect up to 25 families insect pest, including Bemisia tabaci(Gennadius)?Aphis gossypii Glover?Plutella xylostella L. and Spodoptera litura(Fabricius). In this paper, the survival rates of the 1, 3, 5 generations of B. tabaci nymph and the enzyme activities in nymph infected by I. fumosorosea were analyzed to evaluate the effect of I. fumosorosea on B. tabaci nymph. At the same time, the oviposition of the 1, 3, 5 generations of B. tabaci adult, effect of I.fumosorosea mycelium and ethyl acetate extracts on insect reproductive system were also evaluated to show the effect of B. tabaci reproduction by I. fumosorosea. All the experiments were performed as follows:(1) Effect of I. fumosorosea on survival rate of the 1, 3, 5 generations of B. tabaci nymph. The conidial suspension of I. fumosorosea was used to infect different generations of B. tabaci second instar nymph. The result showed that the survival rates of the 1, 3, 5 generations of B. tabaci treated by one concentration of fungus had no significant difference. The survival rates of the 1, 3, 5 generations of B. tabaci were 51.0%, 54.3%, 59.4% and 39.3%, 41.7%, 44.6%, respectively, after treated by I. fumosorosea with the concentrations of 1×104 conidia /ml and 1×107 conidia/ml, respectively. The survival rates of B. tabaci treated by the same concentration of S22(knocked out chitinase gene) and Z-m T(knocked out protease gene) strains were significantly higher than that treated by the wild-type strain.The survival rates were 67.1%/60.8% and 75.4%/67.1% treated by S22 and Z-m T strain with the concentrations of 1×104 conidia/ml / 1×107 conidia/ml, respectively.(2) Effect of Isaria fumosorosea on 4 enzyme activities in Bemisia tabaci nymphs. The SOD, PO, CAT, POD activities of B. tabaci's nymphs were evaluated after the second instar nymph infected by the wild-type strain and S22 strains of I. fumosorosea. After infection, these enzymes activity of nymph increased with time pass on and then decreased, reaching peak values at 36~60h post infection. In 1×107 concentration of wild-type treatment, the highest values of PO, SOD, POD, CAT activity were 1.3U/(g*min), 33.5U/mg, 164.3U/(g*min), 80.5 U/(g*min), respectively. The PO and POD activities treated by S22 strain were no difference between 0 conidia /ml and 1×107 conidia/ml treatments.(3) Effect of Isaria fumosorosea on Bemisia tabaci reproduction. Effect of I. fumosorosea on the 1, 3, 5 generations of B. tabaci reproduction was assessed, resulting no significant difference among the egg production of 1, 3, 5 generations of B. tabaci infected by the wild-type strain. There was a significant difference in the egg production of adult from the wild-type strain, S22 and Z-m T strain infected populations. Compared with the egg production of B. tabaci treated with no fungi, the egg production of new emergence adult decreased significantly, with decrease of 58.5%, 53.4%, 51.3% in 1×104 conidia/ml treatment and 89.7%, 85.4%, 84.0% in 1×107 conidia/ml treatment of the 1, 3, 5 generations, respectively. The rates of the 1, 3, 5 generations adult ovary infected by fungi were 66.7%, 33.3%, 14.3% and 75.0%, 50.0%, 20.0% in 1×104 conidia/ml and 1×107 conidia/ml treatment, respectively. Compared with the egg production of B. tabaci treated with no fungi, the egg production of new emergence adult decreased significantly, with egg production decrease of 52.1% / 70.4 and 48.1% / 68.7% in 1×104 conidia/ml / 1×107 conidia/ml of S22 and Z-m T strain treatments.(4) Effect of Isaria fumosorosea on Bemisia tabaci's reproductive system. The ovarian morphology of new emergence adult was damaged in different degrees after B. tabaci second instar nymph of the 1, 3, 5 generations infected by I. fumosorosea. The number of ovarian ducts and matured eggs decreased sharply after B. tabaci treated with fungi, with decrease of 30~45% / 40~55% and 45~60% / 55~75% in 1×104 / 1×107 conidia/ml treatment. After inoculating the I. fumosorosea spores 42 h, mycelium intruded into whiteflies' isolated fat body tissue, livetin and eggs densely, deformed the ovary. After adding I. fumosorosea crude extract 6h to the whiteflies' isolated ovary, fat body of whiteflies began to degrade, eggs started to shrivel, and the structure of livetin became loose, then livetin degrade gradually. The phenomenon of degradation turned obvious after 24 h. |
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