I can't remember exactly what they use, and it's probably changed anyway since I trained, but they will have a rigorous and extensive regime of pesticide use at regular intervals - I wouldn't enquire too closely, it'll put you off ever eating commercially grown produce again! I should also point out that the pesticides and herbicides available to commercial growers are often not available to the general public, being classed as extremely hazardous substances for controlled use only.

They spray as Bamboo says. If yours have problems (ours do occasionally) then first action is to power spray the plants at the first sign of trouble, this keeps the sprouts clean while they form and after that nothing gets inside them.
Hand pick caterpillars.
Bishop bug (big grey floury aphids) we bite the bullet and spray with a horticultural soft soap again before the sprouts form and get tight.