Poisoning of bees


Bees are in quite a unique position as they cover a lot more area than the normal farmed animal.   Their territory will take them through farm land, households and commercial land.  They can therefore be exposed to a wide range of potentially toxic compounds from pollen of exotic plants to insecticides and pesticides.


The clinical signs of poisoning will vary depending on the toxin.  The ones that are going to be noticed by the beekeeper are going to be:

 Acute – typically colony collapse, neurological disorders or piles of dead bees.

Chronic – deformities of the young.



Stages affected




Toxic chemicals


Dead forages.  Perhaps nurse bees affected.  Queen may be ok.

Usually few

Colony collapse.

Weakened colony.

Lots of dead bees in entrance

Plant poisons





California buckweed

Aesculus californica

Young brood

Forage bees

Deformed workers hairless with neurological problems. 

Call look like Chronic paralysis. Queens may become infertile

Drone brood produced.  Workers die after emergence.  Brood becomes uncapped

Progressively weakened hive.

Queen becomes superseded.  Dead workers at entrance.

Yellow Jessamine

Gelsemium semperviens


Young adults die. Older adults normal

Pupae die in cells and become mummified

Hive slightly weakened

Loco plants

Pupae, Adult – queen.

Forage bees die away from hive.  Those return with neurological issues.  Queen may die

Many cells contain dried pupae

Colony collapse.

Dwindling colony

False Hellebore

Veratrum californicum


Forage bees die away from hive.  Adults die in a curled state.  Queen normal

No effect

Forage bee loss – reduction in production

Southern Leatherwood

Cyrilla racerniflora


No effect

Many blue or purple larvae.

Slight to severe weakening of the hive.


Milkweed pollinia (Aslepias spp)

The pollen is coherent – in pairs connected by a slender filament (the pollinia) – which looks like a bird’s wishbone.   When the forager collects the pollen they can become ensnared and cannot free themselves from the plant.  Those that do can have difficulty getting back to the hive with the pollinia still attached to their bodies.