Deletion genotypes influence occlusion body potency and production in insects infected by a Spodoptera frugiperda nucleopolyhedrovirus isolate from Colombia

Abstract: The Colombian field isolate (SfCOL-wt) of Spodoptera frugiperda multiplenucleopolyhedrovirus (SfMNPV) is a mixture of different genotypes. To evaluate the insecticidalproperties of the different variants in SfCOL-wt a plaque assay was performed and ten distinctgenotypes were identified. Genotype SfCOL-A was the most prevalent (71%) and showed a PstIrestriction profile identical to that of SfCOL-wt. The remaining nine genotypes presentedgenomic deletions of 3.8-21.8 Kb that affected the region between open reading frames (ORFs)sf20 and sf33. The potency of SfCOL-A occlusion bodies (OBs) was approximately 4-fold higherthan SfCOL-wt OBs, whereas the speed of kill of SfCOL-A was similar to that of SfCOL-wt.Deletion genotype OBs were similarly or less potent than SfCOL-wt, but six deletion genotypeswere faster killing than SfCOL-wt. The potency of mixtures of OBs and co-occluded mixedgenotype OBs were consistently reduced in two-genotype mixtures involving equal proportionsof SfCOL-A and one of three deletion genotypes (SfCOL-C, -D or -F). Speed of kill and OBproduction were improved only when certain genotype mixtures were co-occluded, although OBproduction was higher in the SfCOL-wt isolate than in any of the genotypes or genotype mixturesthat we tested. The SfCOL-wt population appears to be structured to maximize the production ofOBs in each infected host suggesting this to be the principal limitation to transmission.