Herbivory below ground and biological weed control: life history of a root-boring weevil on purple loosestrife.
The life history of the root-boring weevil Hylobius transversovittatus was studied in N. and central Europe. The weevil was found to develop on purple loosestrife (Lythrum salicaria), a perennial marshland plant that has become a problem weed in N. America. It was found in all habitats of its host plant with the exception of permanently flooded sites. H. transversovittatus attacked L. salicaria in an early successional stage, devastating large parts of the plants storage tissue. The beetle was found in two-thirds of the field plant populations examined, with a mean attack rate of 76.3%. Larvae developed according to a 1- or 2-year generation cycle depending on the time of oviposition. Adult beetles developing within 1 year emerged between July and Oct., whereas beetles with a 2-year larval period emerged within 3 weeks in July and Aug. Adults were long-lived and could hibernate several times. Beetles of the new generation mated immediately after emergence and some oviposited prior to overwintering. Hibernated females had a oviposition period from May to early Sep. and produced 3-4 eggs/d during the peak ovipositing period. Specific mortality factors were scarce. Dispersal flights ensured the regular occurrence of H. transversovittatus in scattered L. salicaria populations. The severe impact of the weevil is expected to reduce the competitive ability of its host plant after its introduction into N. America.