Stem weevil (Lixus divaricatus)

Systematic position. This species belongs to the order Coleoptera and the family Curculionidae (true weevils). The Lixus genus includes various species specialized in feeding on Amaranthaceae plants, with Lixus divaricatus being a notable representative that interacts with host plants in the Chenopodioideae subfamily.

Affected crops. The pest primarily colonizes wild plant species such as Chenopodium (goosefoot) and Atriplex (saltbush). However, in agricultural settings, Lixus divaricatus can cause significant damage to sugar beet, table beet, and fodder beet fields. The presence of nearby wild hosts often facilitates the migration of the pest to cultivated crops.

Biology and lifecycle. The weevil undergoes a complete metamorphosis. Adult beetles typically overwinter in the soil or under debris. In spring, they emerge to feed on wild host plants before mating. Females deposit eggs by puncturing the stems or leaf stalks of their host. Upon hatching, larvae burrow into the stem, where they consume the inner tissues for the duration of their development.

Nature of damage. The primary injury is caused by the larval feeding activity inside the plant stems. This creates internal galleries that disrupt nutrient and water transport, leading to wilting, plant stunting, and reduced root development in beet crops. These internal wounds can also become entry points for various bacterial and fungal pathogens, further exacerbating the decline of the plant.

Control measures. Management strategies should be multifaceted to be effective:

• Removal of wild host plants, particularly Chenopodiaceae, to eliminate breeding sites.
• Crop rotation practices to prevent the build-up of overwintering populations in the soil.
• Tillage techniques, such as deep autumn plowing, to disturb the habitat of overwintering adults.
• Judicious use of chemical insecticides when monitoring confirms population levels exceed the economic injury threshold.