Much work on biological control of insects has been done in

Which of the following is an effective medicine for diseases in cereal crops and vegetables?

Which microorganism is used to control pests that are harmful to cotton?

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?

Trichoderma harzianum has proven to be a useful microorganism for ...........

Which weed has been eradicated by biological control?