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Pathogenesis of Autographa californica M nucleopolyhedrovirus in fifth instar Anticarsia gemmatalis larvae

California State University, Long Beach

¹ E-mail: ehaas{at}csulb.edu

We have investigated infection and pathogenesis of Autographa californica M Nucleopolyhedrovirus in Anticarsia gemmatalis larvae (velvetbean caterpillar), using a lacZ recombinant virus (AcMNPV-hsp70/lacZ) to track the temporal progression of infection in the midgut intestine and haemocoel. A. gemmatalis was highly resistant to fatal infection by occlusion bodies (OB; LD₅₀>5.5 x 10⁵ OB) and budded virus (BV; LD₅₀>3 x 10⁵ BV) administered via the oral and systemic routes, respectively. Orally administered occlusion derived virus (ODV) efficiently attached and fused to midgut cells, however high levels of infection-induced apoptosis limited infection in the midgut. Transcriptional analysis of AcMNPV genes expressed in the midgut tissues of OB-inoculated A. gemmatalis larvae showed high levels of mRNA encoding the major capsid protein VP39 in the absence of immediate-early transactivator 1 (ie-1) expression. In the midgut, virus was efficiently transferred from infected midgut epithelial cells to nearby tracheolar cells and circulating haemocytes to initiate systemic infection in the heamocoel. However, haemocoelic BV did not efficiently disseminate infection and only cuticular epidermal cells displayed high levels of viral infection. Flow cytometry analysis of haemocytes isolated from BV-inoculated A. gemmatalis larvae showed low level expression of the BV envelope protein GP64 on the cell surface, pointing to a limited capacity for A. gemmatalis heamocytes to amplify virus. These results show that AcMNPV is not an effective biological control agent for limiting crop damage caused by A. gemmatalis larvae.

Received 10 March 2009; accepted 2 May 2009.