Stomach poisons are those:

Sporeine was developed in

Which of the following is not the belief of an organic farmer?

The first bioinsecticide developed on a commercial scale was

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?

What is the main difficulty in the biological control of pests?