Lucerne moth

The lucerne moth (Cydia medicaginis) belongs to the Tortricidae family of the order Lepidoptera. The adult moth has a wingspan of approximately 12–14 mm. The forewings are brownish-grey with a metallic sheen, while the hindwings are lighter in color.

The larvae, or caterpillars, reach 8–10 mm in length. They are typically whitish or yellowish with a dark brown or black head. As they mature, their bodies become more robust, and they display distinct dark markings on their thoracic segments.

The pupae are light brown and roughly 6 mm long, encased in a silk cocoon. The species overwinters as a mature larva in the soil, which allows it to remain protected from winter temperature fluctuations until pupation occurs in the spring.

This pest is a significant threat to alfalfa seed production. The larvae specifically target the reproductive structures of the plant, focusing on developing pods to feed on the growing seeds inside.

A single larva can consume multiple seeds within a pod, drastically reducing the quality and quantity of the harvest. The damage is most severe during the milky to dough stages of seed development, where the nutritional content is highest.

High infestation levels can result in premature pod ripening and shedding. Without proper management, farmers may experience severe losses, rendering the seed crop economically unviable due to the destruction of the embryos within the seeds.

The emergence of the adult moths typically aligns with the onset of the alfalfa flowering period. This synchronization is crucial, as the females rely on the blossoms and young pods for egg-laying sites.

Each female can lay up to 100 eggs, often placing them individually on sepals or young fruit. The larval stage lasts about 7 to 12 days, during which they bore into the pods to feed on the developing seeds before maturing.

The number of generations per year varies depending on the climate, typically ranging from one to three. Late-season generations conclude their life cycle by migrating to the soil to initiate the overwintering process.

Symptoms of an infestation include the presence of fine webbing connecting the alfalfa inflorescences. This webbing is created by the larvae as they move between the seed pods to access food sources.

Visual inspection of the pods often reveals small entry holes surrounded by larval excrement. Once opened, the pods show clear signs of feeding, with seeds appearing hollowed out, partially consumed, or reduced to fine debris.

• Fine silk webbing on the floral clusters.
• Yellowing or premature drying of seed pods.
• Visible entry holes on the pod surface.
• Hollowed-out seeds found inside the pods upon dissection.

Cultural control practices, such as deep autumn plowing, are highly effective in destroying the overwintering larvae in the soil. Proper spatial separation between different alfalfa seed fields also helps prevent the spread of the pest.

Chemical control should be applied during the peak flight of the moths or shortly before egg-hatching. Effective insecticides, including pyrethroids, are used to manage populations before the larvae gain entry into the protective pod environment.

Biological control methods, such as the release of egg parasitoids like Trichogramma, are encouraged. Integrated Pest Management (IPM) strategies emphasize monitoring population levels to ensure that chemical applications are timed correctly to minimize environmental impact.