It was a hot topic at a National Beekeepers' Association meeting he attended on Monday.
The problem was especially hard on people with five to 50 hives wintering near willow trees. Mr Farrer was told wasps had reduced a Hawke's Bay man's 100 hives to 40.
Rob Butcher has been keeping bees for 50 years and fears the aphids will harm conservation as well as the bee industry. He had always had wasp problems, but never the "ruthless destruction" of this season.
The honey made by bees eating the honeydew was in "a comb, set like plastic glass, with sticky runny fluid that resists extraction," Mr Butcher said.
Mr Farrer said the honey had a different sugar, and he called it "concrete honey". It fed bees over winter, but clogged filters and had no other use.
The other reason the aphids were bad news for beekeepers was their effect on willow trees.
"We rely on the willows in spring, because they're a great producer of pollen and nectar for bees," Mr Farrer said.
Beekeepers are looking for scientific research that will help, and will discuss the aphids at their national conference in two weeks.