Geranium bronze

The Geranium bronze (Cacyreus marshalli) is a small butterfly of the Lycaenidae family that has become a major pest for Pelargonium species worldwide. Originally native to South Africa, it has successfully established itself in many temperate regions, causing significant economic damage to nursery production and private gardens.

The host plants are primarily species within the Geraniaceae family. The butterfly prefers to lay eggs on the flower buds, sepals, or stems. Because the larvae are small and cryptic, infestations often go unnoticed until visible structural damage to the host plant is already quite advanced.

The life cycle begins with eggs, which hatch into larvae that bore directly into the flower buds. As they mature, these caterpillars move into the stems to feed on the interior pith. This boring behavior provides them with protection from predators and many contact-based insecticide sprays, making them difficult to eradicate.

The damage is characterized by hollowed-out buds that fail to open, wilted shoots, and the presence of frass (larval excrement) near the entry holes on the stems. In heavy infestations, the entire plant structure weakens, leading to stunted growth, secondary fungal infections, and eventual death of the specimen.

Effective control strategies require an integrated approach. Growers should conduct regular inspections for entry holes and withered buds. Applying systemic insecticides that are absorbed into the plant vascular system is the most reliable method for targeting internal larvae. Additionally, strict sanitation by removing infested material helps to limit the pest's spread.