Submitted to: Gordon Research Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: February 3, 2002
Publication Date: February 3, 2002
Citation: BECNEL, J.J., WHITE, S.E. A NEWLY-DISCOVERED BACULOVIRUS FROM THE MOSQUITOES CULEX NIGRIPALPUS AND CULEX QUINQUEFASCIATUS REQUIRES MAGNESIUM FOR TRANSMISSION. GORDON RESEARCH CONFERENCE PROCEEDINGS. 2002. p.3. Technical Abstract: Baculoviruses that are pathogenic for insects have been intensively investigated due to their potential as biological control agents and because of their importance as gene expression vectors in invertebrate and vertebrate cells. They naturally infect only arthropods and most have been isolated from the Lepidoptera but they are also known from the Hymenoptera, Diptera, Trichoptera and Crustacea. Dipteran (mosquito) baculoviruses, unlike those from Lepidoptera, have been difficult if not impossible to transmit to the mosquito host and therefore basic biological studies have been greatly hindered. We have discovered a baculovirus that caused repeated and extended epizootics in field populations of the mosquitoes Culex nigripalpus and Culex quinquefasciatus over a two-year period in Florida. These mosquito species are important vectors of St. Louis and Eastern equine encephalitis in the United States. Our initial attempts to transmit this baculovirus to larval mosquitoes in the laboratory were unsuccessful. A salt mixture similar to that found in water supporting infection in the field was used in laboratory bioassays and indicated that certain salts were crucial to transmission of the virus. Further investigations revealed conclusively that transmission is mediated by divalent cations: magnesium is essential, whereas the presence of calcium inhibits the activity of magnesium to mediate transmission. A cascade of events is required for infection of a host with a baculovirus. This involves: i) release of virions from occlusion bodies in the insect gut, ii) the movement of virions across the peritrophic matrix (PM), iii) the attachment of virions to the midgut epithelial cells and the transfer of the nucleocapsids to the nucleus where they undergo replication, iv) virions then bud from the midgut cell and spread the infection within the insect. To produce high levels of infection, Mg2+ must be present during the first 8-12 hours of CuniNPV exposure indicating that the activity of Mg2+ occurs early in the process with either entry into the cells or nuclei. Electron microscopic observations of occlusion bodies in the midgut lumen revealed that Mg2+ was not required for dissolution. Other possible targets are receptors on migut epithelial cells or PM or enzymes associated with the virion or midgut that are required for initiating infectivity. Receptors may require divalent cations for the attachment to and/or passage of virions through the PM, midgut cells or entry into nuclei.