The European Spruce Sawflies Pose a Potential Threat to Spruce

The European spruce sawflies pose a potential threat to spruce forests.Baculoviruses have proven to be highly effective biological control agents against these sawflies.Why would pest managers prefer to use a baculovirus rather than a predator feeding on the pest?

A) The baculovirus particles are harmless to vertebrates.
B) Each type of baculovirus only kills a small number of host species.
C) The virus cannot replicate outside of a host cell.
D) All of the above are reasons a baculovirus would be preferred over a predator.