Ryanoid

Ryanoid refers to a class of natural products derived from the plant Ryania speciosa and related species, including the well-known compound ryanodine. Collectively, these compounds are called ryanoids. They have been studied and used for their insecticidal properties, particularly in the mid-20th century, when botanical insecticides were explored as alternatives to synthetic chemicals. Ryanoids are typically described as diterpenoid alkaloids with complex, polycyclic, and often lactone-containing structures. The exact structures vary among individual ryanoids, but they share a common origin and mechanism of action.

The defining characteristic of ryanoids is their interaction with ryanodine receptors (RyR), which are calcium release channels located on the sarcoplasmic reticulum of muscle cells. Ryanoids bind with high affinity to RyRs, modulating calcium release into the cytoplasm. In insects, this disrupts calcium homeostasis, causing uncontrolled muscle contraction, paralysis, and eventual death. The effect is highly potent and selective to some extent for invertebrate RyRs, though vertebrate RyRs can also be affected, which has implications for safety.

Uses and regulatory status have evolved over time. Ryanoids have been employed as contact insecticides to control pests in agriculture and forestry. However, concerns about vertebrate toxicity, environmental impact, and the development of resistance led to restrictions and the decline of broad use in many regions. Today, ryanoids are primarily of historical interest, with occasional use in specialized or research contexts, and they remain important for understanding RyR biology and the development of new calcium-channel–modulating agents.