Study On The Stability Of Hyphantria Cunea Nuclear Polyhedrosis Virus(HcNPV)

This study investigated the factors including temperature, pH, ultraviolet (UV) radiation, field conditions and storage that influence the stability of Hyphantria cunea nuclear polyhedrosis virus (HcNPV) by bioassay, and the stability of HcNPV was evaluated by the mortality of infected fall webworm larvae and LT50. The main results were as follows:1. The time-dependent mortality regression equation of HcNPV suspension treated by55℃bath inactivation was y=83.44-0.31x (p<0.01), and LT50rised from12.18d to15.81d. The mortality remained above50%after90min at55℃.The HcNPV powder had a higher tolerance to temperature than the water suspension. Treated after15min, The temperature-dependent mortality regression equation of HcNPV suspension treated by bath and NPV powder treated by oven were y=104.16-0.93x (p<0.01) and y=101.31-0.46x (p<0.01), and the mortalities were17.41%at100℃and53.91%at120℃, respectively.The activity of HcNPV suspension remained about30%after150min at55℃and15min at80℃treated by bath, so HcNPV suspension could tolerate mild temperature (40～60℃) within a sub-long time and high temperature (above80℃) within a short time.2. Under213μw/cm2UV intensity by an UV lamp (30W,200～300nm and253.7nm strongest), the UV radiation time-morbidity regression equation was y=102.46-0.41x (p<0.01). After30min, the radiation intensity-morbidity regression equation was y=110.70-0.06x (p<0.01). The activity of HcNPV remained above55%after120min at213μw/cm2UV intensity and30min at765μw/cm2UV intensity, so HcNPV could tolerate low intensity within a longer time and high intensity within a short time.The infection processes of HcNPV under both different UV radiation time and intensity showed a similar response. The effect mainly appeared at the later infection stages (7to12days), especially infected9days later, rather than pre-infective stage (3to6days).3. HcNPV was most stable in a neutral solution (pH7.0). Both increase and decline of pH values reduced its mortality, but there is no significant difference in mortality of infected larvae under solution of pH6and8to12. With the pH value increasing, the LT50were shortening. In addition, since the solution of pH10and12were not buffer, the final pH became between7and8, but others were stable.4. HcNPV can stay activity in field conditions. The activity of HcNPV remained63.35%after exposed10days in field. Hot and sunny weather was not conducive to keep the activity of HcNPV in June. On the whole, the relative inactivation of hot and sunny weather was higher then the wet weather’s, but the relative inactivation rate of HcNPV after the first day exposed was the lowest.5. The stability of HcNPV was different because of different storage methods. The cryopresevation activity was higher than cryopreserved activity saved for7years; in addition, it was no significant difference among cryopresevation saved for7and3years, cryopreserved for1years and new purification, so cryopresevation was better for long-term storage than cryopreserved.HcNPV saved for5years compares with other preserved years, it had a remarkable rise in LT50and significantly reduces morbidity in host. In the process of its saving, a part of virus had been purified. In this section, cycle of freezing and thawing appeared which was harmful for HcNPV to keep its activity.