Adults of the root feeding weevil overwinter and appear shortly after purple loosestrife shoots begin to grow in spring. Adults are nocturnal (they may be observed feeding on the plant at dusk or on rainy and overcast days) and consume foliage and stem tissue. Females lay white, oval-shaped eggs in plant stems or in the soil close to the host plant from May-September and may live for several years. Larvae burrow into the roots where they feed for 1-2 years. Pupae chambers are found in the upper part of the root and adults emerge between June and October. Adult feeding is of little consequence; however, larval feeding can be very destructive. With increasing attack rates, larval feeding reduces shoot growth, seed output, shoot and root biomass and can ultimately result in plant death. Attack rates vary widely with rootstock age and size (up to one larva per 10 grams of fresh root weight) and up to 40 larvae have been found per rootstock. Large rootstocks can withstand substantial feeding pressure and several larval generations will be necessary before significant impacts can be expected.
Left to right: Hylobius egg, larvae and damage to purple loosestrife.