The baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV) is able to block viral induced apoptosis in cells derived from the fall armyworm Spodoptera frugiperda by expressing the P35 caspase inhibitor. We tested the hypothesis that apoptosis may serve as an antiviral mechanism in S. frugiperda by examining the pathology of AcMNPV infections using a GFP tagged strain of wild type AcMNPV and AcMNPV lacking the p35 gene. Caterpillars injected with high doses of wild type virus show a strong and rapid infection of the epithelial, fat body, and tracheal tissues as well as a slow build up of virus in the blood resulting in the death of the caterpillar after 5-6 days. In contrast, most caterpillars injected with the p35 deletion virus show no signs of infection in the blood or tissues. In the majority of caterpillars that do show infection with the p35 deletion virus, infection is cleared from the fat body within 48 hours and most of the trachea within 72 hours, with some highly localized persistent infection occurring in the muscle, nervous, and tracheal tissue. In a small percentage of caterpillars the infection spreads gradually through the body, destroying much of the fat body and tracheal tissue. Caterpillars infected with P35 deletion virus have low haemolymph viral titers and have few infected haemocytes. Apoptosis has been detected in the fat body tissues of caterpillars infected with the p35 deletion mutant using the TUNEL assay, and tissues from these caterpillars show clear morphological evidence of apoptosis and cell loss.
Species 1: Lepidoptera Noctuidae Spodoptera frugiperda (Fall Armyworm)
Keywords: Autographa californica nucleopolyhedrovirus, insect pathology
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