Alfalfa seed weevil

The alfalfa seed weevil (Tychius tomentosus) belongs to the order Coleoptera and the Curculionidae family. It is a small beetle, typically measuring 2.5–3.5 mm in length.

The body of the pest is oval-shaped and covered with dense, yellowish-grey hairs, which gives it a distinctive matte appearance.

Adult weevils have a characteristic moderately long, slightly curved rostrum (snout) typical of this family of beetles.

The larvae are legless, fleshy, and white or yellowish with a distinct dark head capsule, growing up to 3–4 mm long.

Adults are quite active during sunny weather, but they exhibit a "death-feigning" behavior, falling to the ground and remaining motionless when disturbed.

The primary host plant is alfalfa, specifically its reproductive organs during the budding and flowering stages.

While adults feed on plant tissue, the larvae cause the most damage by consuming the seeds from within the developing pods.

Under favorable conditions for the pest, an infestation can lead to significant yield losses, often destroying over 50% of the seed crop.

Besides alfalfa, the pest may occasionally be found on other perennial legumes growing in the vicinity of primary infestations.

Infestations typically begin at the edges of the field, spreading gradually throughout the stand, which necessitates localized monitoring.

Adult weevils overwinter in the soil or under plant debris in fields where alfalfa was grown during the previous season.

Emergence from hibernation occurs in spring, aligning with the early budding stage of alfalfa, providing the beetles with necessary nutrition.

After a period of maturation feeding, the adults mate, and females deposit their eggs directly into the developing legume pods.

The life cycle of one generation is completed over the summer, after which the larvae exit the pods to pupate in the soil.

New adults emerge from the soil pupal chambers, though they remain dormant until the following spring, completing their annual cycle.

The most visible sign of an infestation is the presence of tiny, circular exit holes on the surface of mature alfalfa pods.

Opening the pods often reveals hollowed-out seeds that have been entirely consumed by the developing larvae.

Adults can be observed during the flowering period, as they are often found nestled within the floral racemes feeding on pollen.

Severe infestations cause premature yellowing and shriveling of the seed clusters, which fail to reach full maturity.

Fields with heavy populations show a notable reduction in total seed yield per hectare compared to uninfested sites.

Deep autumn plowing of harvested seed fields is a key cultural control method that disrupts the overwintering habitat and reduces populations.

Maintaining adequate spatial isolation between new and old alfalfa stands is recommended to limit the migration of the pest.

Chemical control should be implemented during the budding stage, before egg-laying begins, using appropriate registered insecticides.

Monitoring using sweep nets is essential to determine if beetle populations exceed economic thresholds before initiating chemical sprays.

Early harvesting of alfalfa for hay can serve as a non-chemical method to remove the larval host material before the pests finish their development.