Seleção genetica e interação de baculovirus em Diatraea saccharalis (F,1794)

AUTOR(ES)
DATA DE PUBLICAÇÃO

1985

RESUMO

The effects of serial passages of the Nuclear Polyhedrosys Virus of Anticarsia gemmalis (AgNPV) and the Nuclear Polyhedrosys Virus of Trichoplusia ni (VPNTn) through the alternate host, Diatraea saccharalis one of the main pests of sugar cane throughout America, was studied. For each of these experiments more than 5000 larvae of D. saccharalis were individually analysed. It was noted through the reduction of DL50 values that a substantial increase in the virulence of these two baculovírus occurred after being submitted to serial passages through the D. saccharalis. On the first serial passage of the AgNPV the DL50 value was 7,87 X 105) PIBS/larva whereas on the thent passage that value was reduced to 6,65 X 103 PIBs/larva showing that the virus became about one hundred times more virulent to these insects after being submitted times more virulent to these insects after being submitted to ten serial passages. The TnNPV presented in the first serial passage the DL50 value of 9,68 x 104 PIBs/larva whereas in the eleventh serial passages the TnNPV had its virulence increased about eight hundred times when comparted to the original isolate. It was noted that the isolate of the AgNPV adapted to the new host exhibited a reduction of its virulence to the original host, Anticarsia gemmatalis. The isolate of the TnNPV was not tested against its original host, Trichoplusia ni. The results of the present work do not represent the limit of possibilities of selection of these virus (AgNPV and TnNPV), in fact they gave clear evidence of their potential and of the necessity of continuation of these studies aiming a better comprehension of the subject. The AgNPV and the TnNPV had and an expressive improvement of its efficiency by the serial passage method, which represents a simple and low cost method. A study of the effect of the inoculation of the Granulosis Virus of Diatraea aacaharalin (DsGV) associated to both NPV above mentioned was also object of this work. Three types of mixed inocula were used: 1) AgNPV + TnNPV 2) AgNPV + DsGV and 3) TnNPV + DSGV on D. saccharalis larvae. For these experiments more than 3500 larvae of D. saccharalis were individually analysed. Its was observed that, when individually inoculated AgNPV and TnNPV exhibited peaks at around 10 days after ingestion. The inoculum resulting from association of these two viruses (AgNPV + TnNPV) showed a clear dispersion of these peaks from to 10 to 50 days after the inoculation. The two mixed inocula resulting from the association of one NPV and one GV (AgNPV + DsGV and TnNPV + DsGV) presented a clear mortality peak at around 10 days, and other peaks after 20 days with main peaks present at around 30 and 40 days after inoculation. The first mortality peak can be related to the effect of the AgNPV and TnNPV and the peaks after 20 days of inoculation to the effect of DsGV. It was observed that the DsGV is more virulent that TnNPV which, in turn, is more virulent to the larvae of D. saccharalis than the AgNPV; and it was verified that even when in association this pathogenicity order was maintained. The resu1ts of this study demonstrated in a quantitative manner that the interference or antagonism phenomenon occurred in the three types of mixed inocula. For the various combinations of virus and dosagens the resulting mortality response from the associated virus was not higher than that produced on the larvae of D. saccharalis from the action of a single virus. This demonstrates that for practical purposes the AnNPV, TnNPV and the DsGV should not be associated for this type of pest control. Our results showed that the baculovirus here analysed can be genetically manipulated and once associated they show a reciprocal interference as if they were competing for the same tissues and resources of the insect. This interference indicates a homology of systems manifesting in different viruses originated from hosts coming from different Families. In conclusion, our data sugest the existence of great homology in this insect virus group, and that probably due to this fact we can genetically manipulate these important pathogens through relatively simple methods

ASSUNTO(S)

lavoura insetos - seleção virus de plantas

ACESSO AO ARTIGO

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