High levels of genetic variation within Helicoverpa armigera nucleopolyhedrovirus populations in individual host insects

It has been well documented that baculovirus populations exhibit high levels of genetic variation. Due to the lack of sensitivity of the techniques currently used to study baculovirus genetic variation, relatively little is known about baculovirus genetic diversity at the individual insect level. Since denaturing gradient gel electrophoresis (DGGE) has key advantages over other methods used to study genetic variation in baculoviruses, DGGE assays were used to obtain a better understanding of the genetic variation within baculovirus populations in individual host insects. Helicoverpa armigera nucleopolyhedrovirus (HearNPV) was used as a model baculovirus system, and neonate H. armigera larvae were infected with one of two geographically distinct HearNPV isolates. DGGE assays for two lepidopteran-specific baculovirus genes, me53 and dbp1, detected many HearNPV genetic variants within individual host larvae, with up to 20 genetic variants detected in a 434-bp fragment of the dbp1 gene in a single neonate larva. High levels of HearNPV genetic diversity were detected in individual host larvae irrespective of the HearNPV isolate used to infect the larvae. This study sets a benchmark for HearNPV genetic variation in individual H. armigera larvae. The levels of HearNPV genetic diversity detected are higher than reported previously for a baculovirus population at the individual insect level.