http://www.msnbc.msn.com/id/19233858/

After months of study, researchers are finding it difficult to tie the die-off to any single factor, said 
Maryann Frazier, a senior extension associate in Penn State University's entomology department.

"Two things right now ... that are really keeping us focused are the pathogen and the role of 
pesticides," Frazier said.

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