Hundreds of thousands of bees may have been accidentally poisoned at properties in Murchison, near Nelson.
Honey producers are facing massive losses as they discover hundreds of dead hives in the area.
Beekeeper Ricky Leahy made the grim discovery of dead bees at his Murchison property on Friday.
"Oh, I just about burst into tears to be quite frank," he said.
A carpet of carcasses surrounds around 200 hives on the property and another 60 next door.
Mr Leahy suspects accidental poisoning.
"Somebody with the best intent to try and solve their wasp problem, and they've just used a poison which has attracted our bees."
It's recommended that baited 'meat' is used to poison wasps, rather than sugar-based bait, like jam, which also attracts bees.
Mr Leahy said bees which have just hatched are dying.
The Ministry for Primary Industries is investigating and dead bees have been sent to a lab for testing. But results aren't expected for a month.
"To go and buy a queen bee on the market is somewhere around $50 each at the moment," Mr Leahy said, adding that he had about 400 queen bees in a mating yard.
Mr Leahy expected to produce up to 1200 queen bees this season, but now all the affected hives will have to be burnt to prevent poisoning others.