What are the components that are harmful to crops in the field of agriculture commonly called?

Consider the following statements:
$I.$ Ladybirds and dragonflies are used to get rid of aphids and mosquitoes.
$II.$ The bacteria $Bacillus$ $thuringiensis$ $(Bt)$ are used to control butterfly caterpillars.
$III.$ $Trichoderma$ $sp.$,free-living fungi,are present in root ecosystems where they act against several plant pathogens.
$IV.$ $Rhizobium$ is a symbiotic bacterium that lives in the stem of legumes.
Which of the statements given above are correct?

Which virus is responsible for the biological control of insects and arthropods?

Describe the main ideas behind the biological control of pests and diseases.

The phenomenon of using a predator for controlling a pest is known as:

Compared to chemical controllers,how are biocontrol agents for pest control in agriculture?