Transmission Patterns of Natural and Recombinant Baculoviruses

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. The advent of genetically modified organisms such as pathogens has raised ecological questions that need to be addressed in order to assess any risks involved in their use. The baculovirus Autographa californica nucleopolyhedrovirus (AcNPV), which infects a number of lepidopteran species, has been modified to express an insect-selective toxin. This genetic modification increases the speed with which it kills its host. However, in addition to this intended feature of the modified virus, there may be other consequences for the host-pathogen interaction. We report a field experiment in which transmission patterns of the wild-type and the genetically modified baculovirus are measured within and between a model target (susceptible) and nontarget (less susceptible) lepidopteran species. Two foliar feeders were chosen: Trichoplusia ni, the cabbage looper, is highly susceptible to this pathogen, while Mamestra brassicae, the cabbage moth, is semipermissive. These two species are used as both the source and the recipients of infection for both virus types. A series of models are fitted to determine the probabilities of infection (given survival from other sources of mortality) over a 7-d period within contained field cages. Fitting these models to data illustrates that a substantial fraction of the population escapes infection, and it is the size of the pathogen-free refuge that varies between treatments. When infected individuals from the less susceptible species die, the yield of virus is greater than from susceptible hosts, yet this does not significantly alter the risk of transmission to other hosts. In contrast, the genetically modified baculovirus always results in a lower risk of infection in the field compared to the wild type. This is because the recombinant virus causes paralysis, and as a result, the cadaver may fall from the plant before death and virus release. Hence the number of cadavers remaining on the foliage has a greater influence on transmission than the yield of virus from those cadavers.

Transmission dynamics of an iridescent virus in an experimental mosquito population: the role of host density

“…the fraction of the population that occupy the pathogen-free refuge. Parameter estimation was performed in S-Plus (Crawley, 2002) and model simplification, by sequential removal of terms from the full refuge model, was undertaken as described by Hails et al (2002). Models were corrected for minor overdispersion (scale parameter ¼ 2.27).…”

“…Heterogeneity in host susceptibility can also generate nonlinearities in the probability of transmission (Dwyer et al, 1997;Reeson et al, 2000). Recently, Hails et al (2002) have addressed non-linear patterns of transmission by considering that a fraction of the surviving host population may not come into contact with an infective dose of pathogen or may be innately resistant to infection. This sub-population occupies a pathogen-free refuge, the size of which may vary according to host or pathogen densities.…”

Deletion ofv-chiAfrom a Baculovirus Reduces Horizontal Transmission in the Field

“…The functions of these liquefaction-related genes and their products may have serious ramifications for the efficacy and persistence of control agents derived from them. However, because most studies of microbial pesticides focus on the initial response of pests to a sprayed product, the effect of genotype on subsequent horizontal transmission remains largely unexplored, with the exception of some engineered viruses (1,27).…”

“…BV is then produced within larvae early during infection, budding from the plasma membrane and infecting other cell types to cause a systemic infection. During the late phase of infection, ODV are produced and become embedded into polyhedra, and the infection process terminates upon larval death (1). Many NPVs code for proteins that degrade the larval integument, aiding in the release of polyhedra contained within the larvae (2).…”

“…N ucleopolyhedroviruses (NPVs) are viruses belonging to the Baculoviridae, members of which infect insects and other arthropods (1). NPVs possess large circular and double-stranded DNA genomes and have a unique infection cycle.…”