Biological control of pests is

Which insect is used to control the spread of prickly pear cactus $(Opuntia)$?

The common biological control agent for plant diseases is ......

'Rotenone' is

Assertion $A$: The use of biocontrol agents prepared by microorganisms has become necessary as an alternative to chemical pesticides.
Reason $R$: The use of biological control agents helps maintain the balance of the ecosystem.
Which option is correct for Assertion $A$ and Reason $R$?

What type of fungus is $Trichoderma$?