Cabbage stem weevil

Systematic position: Calosirus terminatus is a species of weevil belonging to the order Coleoptera and the family Curculionidae. It is a well-documented pest known to cause economic losses in agricultural regions where brassicaceous crops are intensively cultivated.

Host crops: This insect primarily attacks plants within the Brassicaceae family. Its main hosts include oilseed rape (canola), various cultivars of cabbage, mustard, and turnip. The presence of wild cruciferous weeds often sustains pest populations outside of the cropping season.

Biology and life cycle: The adult weevils overwinter in the soil or within plant debris. As temperatures rise in spring, they emerge to feed on the foliage of emerging host plants. Females lay eggs directly into the leaf petioles or main stems. Upon hatching, the larvae tunnel into the plant tissues, feeding internally before dropping to the soil to pupate. The species typically completes one generation per year.

Damage and harmfulness: The larval stage is the most destructive, as they create internal tunnels within the petioles and stems. This physical damage stunts plant growth and causes leaf deformation. Furthermore, the larval feeding sites act as entry points for various fungal and bacterial pathogens, which can lead to stem rot and systemic weakness of the crop, significantly reducing yield quality and quantity.

Protection measures: Effective management requires an integrated approach. Crop rotation is essential to prevent the accumulation of soil-dwelling pupae. Mechanical control, such as deep autumn ploughing, helps disturb the overwintering sites. Monitoring for adult weevils in early spring is crucial; if population densities exceed the economic threshold, targeted applications of systemic insecticides should be employed before egg-laying begins.