Submitted to: Society of Invertebrate Pathology
Publication Type: Abstract Only
Publication Acceptance Date: July 26, 2003
Publication Date: July 26, 2003
Citation: POPHAM, H.J., SHELBY, K., BRANDT, S.L. Virucidal activity against HzSNPV in naive plasma of Heliothis virescens (Lepidoptera: Noctuidae). SOCIETY OF INVERTEBRATE PATHOLOGY. 2003. Abstract p. 39. Technical Abstract: Lepidopteran larvae are known to resist baculovirus infection by selective apoptosis or sloughing off of infected cells from the midgut. Once the baculovirus infection breaches the midgut barrier, however, there are few known mechanisms to account for the resistance and clearance of infection observed in some virus/host combinations. For example, encapsulation and melanization of AcMNPV infective foci in tracheoblast cells of H. virescens and M. sexta have been reported, and these processes were inhibited by prior polydnavirus infection or parasitization. Phenoloxidase of H. virescens has also been reported to inactivate several viruses in vitro. We tested the hypothesis that a factor(s) present in the plasma of infected pest larvae could act to limit the spread of baculoviruses within the hemocoel. We have developed an in vitro bioassay in which Helicoverpa zea single nucleopolyhedrovirus (HzSNPV) particles are incubated with plasma collected from uninfected Heliothis virescens larvae. The TCID50/ml (50% tissue-culture infectious dose) of surviving HzSNPV were then titered on HzAM1 cells. In vitro incubation with diluted naive plasma from larval H. virescens exhibited a virucidal effect against HzSNPV, reducing the TCID50/ml by more than 40 fold (7.7 + or - 3.3 x 10**5 to 1.8 + or - 1.3 x 10**4). The virucidal activity was freeze-stable but heat- and protease-labile. Activity was highest in plasma from early fourth instar larvae. We will report on the biological and biochemical characterization of this constitutive humoral antiviral resistance mechanism in insects, and the linkage of this activity to the inducible antimicrobial response.