Black stem weevil

Systematic position. The black stem weevil, Tyloderma nigrum, belongs to the order Coleoptera and the family Curculionidae. This species is characterized by its endophytic lifestyle, meaning it spends the majority of its larval stage protected inside the host plant's stem, making it a challenging pest to manage with surface-level applications.

Host plants and damage. The pest primarily targets plants within the Asteraceae family. Larvae burrow into the stems, creating galleries that disrupt the plant's vascular system. This infestation often leads to stunted growth, wilting, and stem breakage, which significantly impacts both the aesthetic value of ornamental plants and the biomass production of forage crops.

Biology and life cycle. Tyloderma nigrum undergoes complete metamorphosis. Adults typically overwinter in soil or leaf litter, emerging in the spring to feed and mate. Females oviposit on the stems or leaf axils, and upon hatching, the larvae bore into the interior of the plant. The larvae complete their development within the stem, eventually pupating inside the gallery they have created.

Nature of damage. Signs of infestation include small entry holes on the stems, often accompanied by gall-like swellings or necrotic tissue. As the larvae consume the internal pith, the structural integrity of the stem is compromised. Infested plants show symptoms of chlorosis, reduced vigor, and in severe cases, the affected stems may snap under environmental stress or heavy wind.

Control measures. Effective management requires an integrated approach focusing on prevention and targeted chemical intervention:

• Strict sanitation practices, including the removal and destruction of crop residues after harvest to reduce overwintering populations.
• Crop rotation to break the pest's life cycle by removing preferred host plants.
• Application of systemic insecticides during the peak activity period of adult weevils before egg-laying begins.
• Monitoring of stem integrity throughout the growing season to detect early infestation signs.