In the mountains of Mexico's tropical sierra, an ever-growing expanse of pink poppy flowers has pushed prices so low for opium paste, the gummy raw ingredient of heroin, that farmer Santiago Sanchez worries how he will feed and clothe his family. The area of Mexico that illegally farms opium poppies grew by more than one-fifth last year, to an area the size of Philadelphia, according to a U.N.-backed study published in November. That, along with a trend toward mixing synthetic opiate fentanyl in Mexico's tarry black heroin, has slashed what criminal gangs pay farmers like Sanchez for a kilo of opium. Now, Sanchez earns about $260 per kilo, a fifth of the average price two years ago. While Mexico's top drug traffickers still make billions of dollars supplying U.S. addicts, at the bottom of the supply chain, the villagers are hardly surviving. REUTERS/Carlos Jasso SEARCH "JASSO OPIUM" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGES OF THE DAY. Matching text: MEXICO-DRUGS/