An army helicopter flies over verdant mountains in the state of Guerrero, Mexico, the scene of unusual coca crop discoveries that suggest drug cartels are adapting to shifts in the multimillion-dollar narcotics trade. For years, poppies -- the raw material for heroin -- and marijuana have provided a livelihood for thousands of farmers. But in recent years, the growing US addiction crisis surrounding fentanyl has caused opium demand to fall. The result is that Mexican traffickers are now increasingly growing coca leaves, whose production has historically been dominated by Bolivia, Peru and Colombia. IMAGES AND SOUNDBITES