Hemp moth

The hemp moth (Grapholita delineana) is a lepidopteran insect belonging to the family Tortricidae. It is considered a major pest of cultivated hemp, as its larvae feed specifically on the tissues of Cannabis sativa. Due to its specialization, it can cause severe economic losses in both fiber and seed production operations.

The primary host plant is the hemp plant. The moth attacks the plant at various stages of its development, showing a preference for tender apical shoots and floral structures. This behavior makes it particularly destructive during the flowering phase, when the plant is investing energy into seed and metabolite production.

The biological cycle consists of four stages: egg, larva, pupa, and adult. The insect typically undergoes several generations per year depending on the climatic conditions. Pupation occurs within the stems of the plant or in plant debris near the soil surface, where they overwinter to emerge in the spring once temperatures stabilize.

Damage symptoms include wilting and deformation of the main stem, commonly referred to as «top-galling». Larvae bore into the stalk, which weakens the plant structurally and disrupts nutrient flow. When they attack inflorescences, they consume floral parts and developing seeds, directly impacting the final yield and oil content of the harvest.

Integrated Pest Management (IPM) is crucial for controlling Grapholita delineana. Recommended practices include:

• Destruction of crop residues post-harvest to remove overwintering sites.
• Monitoring adult populations using pheromone traps to time insecticide applications accurately.
• Application of bio-rational insecticides such as Bacillus thuringiensis or specific chemical controls during the egg-hatching period.
• Maintaining field hygiene to prevent the buildup of pest pressure over successive seasons.