Geranium bronze

The Geranium bronze (Cacyreus marshalli) is a significant pest belonging to the order Lepidoptera and the family Lycaenidae. Originally native to South Africa, it has become a major invasive species across Europe, causing extensive damage to cultivated geraniums and pelargoniums.

The larvae (caterpillars) of this moth are highly specialized feeders, primarily targeting species within the genus Pelargonium. They are cryptic feeders, meaning they often tunnel inside stems, buds, and flowers, making them invisible to the casual observer until significant damage has already occurred.

The life cycle begins when adult butterflies lay eggs on the leaves or flower buds of the host plant. Once hatched, the larvae immediately start feeding on the tissue. As they grow, they bore into the stems, where they live and feed, protected from external predators and many contact insecticides.

The damage caused by Cacyreus marshalli is characterized by withered buds, stunted growth, and hollowed stems, which often break under the weight of the plant. A heavy infestation can lead to the death of the entire plant, as the caterpillars disrupt the nutrient flow by feeding on the internal stem tissue.

Effective management strategies include:

• Frequent inspection of plants for signs of entry holes and frass near the base of buds.
• Physical removal and destruction of infested stems and flower buds.
• Application of systemic insecticides that are transported within the plant tissues to reach the larvae.
• Monitoring the presence of adult butterflies using pheromone traps.
• Implementing biological control measures, including the use of entomopathogenic nematodes or bacteria.