The poisonous toxin in New Zealand tutu plants that can contaminate honey is tutin.
Tutin is a potent plant-derived neurotoxin found in several Coriaria species, collectively known in New Zealand as tutu. It is a convulsant that interferes with glycine receptors, and serious exposure can cause nausea, vomiting, dizziness, delirium, seizures, coma, or death.
The honey connection is unusual because bees generally do not collect tutin directly from tutu flowers. Instead, passion-vine hoppers feed on tutu sap and excrete honeydew containing the toxin. Bees may gather this honeydew, allowing tutin to enter honey and occasionally cause toxic-honey outbreaks.
Tutin was first isolated in 1901 by New Zealand chemists Easterfield and Aston. Historically, poisoning also affected livestock and settlers. A common mix-up is picrotoxin: it has similar convulsant effects, but tutin is the named toxin associated with New Zealand tutu honey.