Spodoptera Litura Nuclear Polyhedrosis Virus Spread In Host Populations

In this study, we investigated the vertical transmission of Nuclear Polyhedrosis virus on S. litura, and the oviposition behavior of Microplitis sp. on virus infected and noninfected S. litura larvae.Through the investigation, we can well realize the development and propagation of present generation especially the progeny generation while infected with virus, and the interactions between virus, S. litura and Microplitis sp..1 The sublethal effects and vertical transmission of SINPVThe experiments were conducted to determine the effects of vertical transmission to the present and progeny of S. litura. In this experiments, we conducted 2 ways to infected the S. litura.The one is to infect the adults, the other is to infect the larvae. While infected the adults, the results showed that through the vertical transmission, the larva mortality of F1 progeny was 10.62%-30.23%, and the larva mortality of F2 progeny was 6.26%-23.33%. The percents of pupation and eclosion were both decreased while infected with virus. Compared to the control, F1 progeny of pupation percent was decreased 34.63%, and the eclosion percent was decreased 19.61%; F2 progeny of pupation percent was decreased 9.84%, and the eclosion percent was decrease 12%. Also, the period of oviposition and the quantity of eggs was decreased while infected with virus, and it increased with the generation. Compared to the control, the period of oviposition was decreased 1.20 days at the most, and the quantity of eggs was decreased 352.33 at the most. The sex ratio of adults was also affected by the virus, the percent of female adults was decreased while infected with virus. And the longevity of infected adults was decreased.While infected in the larvae stage, we set the virus to infect the 2-6 instar larvae, The experiments were conducted to determine the effect of vertical transmission to the present and progeny of S. litura while infected in different instar. The results showed that mortality of F₁ progeny reached at 16.67%³3.33%, the F₂ progeny reached at 6.25%⁸.75%. And the highest mortality reached at 6-8days after infected. The percent of pupation and eclosion were both decreased while infected with virus, and they were increased with the generation. F₁ progeny of pupation and eclosion percent were 73.08%⁷8.94%, 73.68%⁷5.00%; F₂ progeny of pupation and eclosion percent were 79.45%⁸3.78%, 80.00%⁸2.76%. The periods of oviposition and the quantity of eggs were decreased while infected with virus, and it was increased with the generation. Compared to the control, the period of oviposition and the quantity of eggs was decreased 1.06 days and 268.82 separately. The sex ratio of adults was also affected by the virus, the percent of female adults was decreased while infected with virus. And the longevity of infected adults was decreased.2 Investigations on transmission of SINPV induced by sex attractantIn this experiment, we set 3 virus concentrations, and the adults were carried with virus induced by sex attractant in fields.The TDM model was used in this experiment, and it was conducted to determine the mortality time dynamic of vertical transmission to the progeny of S. litura. The results showed that the adults in the field can transmit the virus to the F1 progeny, and 5days after hatched, F₁ progeny of virus treated reached the highest mortality. while the virus concentrations increased, the values of LT₅₀ decreased, while the concentration was 200X, the value of LT50 was 8.9928, while the concentration was 50X, the value of LT₅₀ was 6.4256.3 Cooperative effects of S. litura nuclear polyhedrosis virus with parasite wasp, Microplitis sp. on the S. litura larvaeParasitoid behavior and oviposition were monitored to investigate the ability of Microplitis sp. to distinguish between SINPV-infected and noninfected larvae of S. litura, and the capacity of parasite to vector virus was also determined in laboratory. The results showed that the parasitoid prefered to lay eggs on noninfected larvae after 3 days post virus inoculation. Searching time, however, differed significantly after 3 days post virus inoculation. Time of attacks differed significantly after 2(virus concentration was 9.44×10⁶ PIB/ml), 3 (virus concentration was 1.89×10⁶ PIB/ml)days post virus inoculation. First attack of virus treatment was lower than noninfected treatment, and the longer the time interval between exposure to virus and subsequent exposure to parasitoid females, the more parasitoid chose the noninfected larvae. The percent of cocoons was decreased with the time interval between exposure to virus and subsequent exposure to parasitoid females. Compared to the controls, percent of adults was lower, and it was not related to the time interval between exposure to virus and subsequent exposure to parasitoid females. The female parasites which developed or oviposited in virus-infected hosts , and manually contaminated the ovipositor of the females with virus suspension could all carry infective doses of the virus, and transmit virus from infected larvae to healthy larvae through ovipositor. A female parasite which developed or oviposited in virus - infected hosts transmitted infective doses of the virus to an average of 2.14, 2.45 healthy host larvae exposed to it respectively. Ability of parasite which manually contaminated with virus to transfer the virus increased as the inoculation virus doses increased. A female parasite from the cocoon contaminated with SlNPV of different doses virus could transfer infective doses of the virus to an average of 1.45 healthy host larvae; A female parasite exposed to the mixture of different doses virus and 10% honey-water solution could also transmit virus to an average of 0.94 larva.