Fast accumulation of few polyhedra mutants during passage of a Spodoptera frugiperda multicapsid nucleopolyhedrovirus (Baculoviridae) in Sf9 cell cultures

Baculoviruses are a group of viruses that infect invertebrates and that have been used worldwide as a biopesticide against several insect pests of the Order Lepidoptera. In Brazil, the baculovirus Spodoptera frugiperda multicapsid nucleopolyhedrovirus (SfMNPV; Baculoviridae) has been used experimentally to control S. frugiperda (Lepidoptera: Noctuidae), an important insect pest of corn (maize) fields and other crops. Baculoviruses can be produced either in insect larvae or in cell culture bioreactors. A major limitation to the in vitro production of baculoviruses is the rapid generation of mutants when the virus undergoes passages in cell culture. In order to evaluate the potential of in vitro methods of producing SfMNPV on a large-scale, we have multiplied a Brazilian isolate of this virus in cell culture. Extensive formation of few polyhedra mutants was observed after only two passages in Sf9 cells.     

Population genetic structure determines speed of kill and occlusion body production in Spodoptera frugiperda multiple nucleopolyhedrovirus

A Nicaraguan isolate of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfNIC) survives as a complex mixture of genotypes (named A to I). The speed of kill, time-mortality distribution, and occlusion body (OB) production of single genotypes (A, B and F) and co-occluded mixtures of genotypes, in a 75% + 25% ratio, were compared to determine the contribution of each genotype to the transmissibility of the viral population. Pure genotypes differed markedly in their speed of kill in second instar S. frugiperda. The speed of kill of SfNIC was attenuated compared to that of the dominant genotype B, indicating that interactions involving two or more genotypes likely determine host killing traits in the virus population. Genotypes A, F and defective genotype C, had no significant effects on the distribution of insect deaths over time when present as minority components in mixtures comprising 75% of genotype B. Similarly, the mortality pattern over time of insects infected by genotype F, the fastest-killing genotype tested, was not affected by the presence of genotypes A or C. Semi-quantitative PCR studies indicated that the genetic composition did not differ significantly between SfNIC-infected insects that died soon (67 h) or late (139 h) after inoculation, suggesting that stability in genotypic composition is important for virus survival. Median OB production per insect was correlated with mean time to death so that attenuated speed of kill of SfNIC resulted in high OB yields. We conclude that (i) minority genotypes play a functional role in determining the timing of mortality of infected hosts and (ii) the genotypic structure of the virus population is stably maintained to maximize the likelihood of survival.     

草地贪夜蛾核型多角体病毒对我国草地贪夜蛾不同地理种群毒力的比较分析

草地贪夜蛾Spodoptera frugiperda(J. E. Smith)入侵我国多个地区,逐渐形成地理种群。在草地贪夜蛾核型多角体病毒Spodoptera frugiperda multiple nucleopolyhedrovirus(SfMNPV)生物农药的生产过程中发现,不同地理来源的宿主对SfMNPV的敏感性和产量存在明显差异,显著影响了SfMNPV的生产效率。为解析其敏感性差异及其产生的原因,本研究首先对云南德宏、广东广州、广西钦州、西藏林芝4个地区草地贪夜蛾种群基因型进行了鉴定,采用生物测定法测试SfMNPV对4龄幼虫的口服毒力,然后,通过向幼虫体内注射草地贪夜蛾核多角体病毒出芽型病毒粒子(budded virions, BVs)的方式,越过口服感染中肠的过程,分析敏感性差异发生的阶段。最后比较了高敏感和低敏感种群中肠肠液pH,并基于16S rDNA测序测定了肠道菌群组成。结果表明,广西种群属于纯合玉米型,其余种群为带有水稻型COI标记的杂合玉米型。广西种群对SfMNPV的口服敏感性最低,西藏种群的敏感性最高,但两者注射BV后死亡率差异无统计学意义,暗示病毒敏感性差异...