At least six instances of bee theft have been reported this year in five Californian counties as the almond pollination season begins, according to CNBC. The price for bee rentals has soared this year due to high demand among almond farms, fueling the theft.

Almost 2 million hives have been brought to California this year to pollinate the almond farms at rates as high as $200 a pop.

The California State Beekeepers Association has posted notices about the thefts, offering a reward of up to $10,000 for information leading to the thieves. “We take the issue of hive theft very seriously and are willing to generously reward those who help us stop this growing problem,” the association wrote in a post. The heists appear to be executed by professional beekeepers, since in at least one theft, the perpetrators used a bee forklift.

As Modern Farmer has reported, the theft of bee hives has been on the rise as the number of bees has shrunk. A new study finds that wild bee populations in the US fell 23% in five years, from 2008 to 2013. Climate change, pesticides and other causes have been linked to the decline.

Almond growers are already watching their balance sheets as the price of the nut has recently plummeted due to oversupply. Since late 2014, almond prices have dropped by almost one-quarter.