Bees usually fit into one of two patterns as foragers. Specialist bees are flower-dedicated, usually seeking the nectar of just one or maybe two types of flowers, and even then, usually only one at a time. Then there are generalist bees, and they forage from any and all flowering plants except flowers that are known to make them sick.
Many plants have produced active toxins against which certain specialist insects have developed an evolutionary counter-adaptation. Foothills death-camas, Toxicoscordion paniculatum (Nutt.) Rydberg (formerly Zigadenus), is one such flower.
A study shows that its pollen and nectar contain zygacine, the steroid alkaloid whch causes this notorious plant’s toxicity to mammals. Such flowers are specialists’ pollen hosts but they can also frequently attract a broad number of floral generalist insects too to flowers that are chemically defended.
This 4:36-minute video by Rocky Mountain Edibles shows how to tell the difference between a wild onion and the poisonous look alike, which is Death-camas, or the Death Lily:
When hungry naïve adults of a generalist solitary bee like the orchard mason bee or blue mason bee, Osmia lignaria Say (Megachilidae) briefly drank death-camas nectar, or zygacine in syrup in biologically relevant doses, a few things happened. The neurotoxic alkaloid in the pollen and nectar caused extended bouts of irritable tongue grooming. Many such bees were paralyzed. Some died. If bee larvae provisions were laced with toxic doses, they stopped feeding and sometimes died.
When the generalist solitary bee Osmia lignaria suffers from this poisonous substance, there can be prolonged irritation and even avoidance of foraging.
A survey conducted over a five-state area illustrates why the Osmia lignaria and over 50 other generalist vernal bee species were absent from death-camas flowers.
This 3:39-minute video by Jepson Herbarium shows you what the death-camas looks like:
In contrast, the specialist sole visiting bee, Andrena astragali, foraged exclusively on death-camas flowers for its nectar and pollen. It is the toxic alkaloid found in the nectar and pollen of the death-camas flower that deters generalist bees from such pollinator-dependent flowers. It restricts and dissuades single specialist bees from visiting and permits a single specialist bee that can tolerate the death-camas toxins to pollinate it.
This just goes to show that even in the world of bees, loyalty has it rewards.