Current Status of the Stem-boring Weevil Listronotus setosipennis (Coleoptera: Curculionidae) Introduced Against the Weed Parthenium hysterophorus (Asteraceae) in Australia

Effects of the stem-boring weevil Listronotus setosipennis (Coleoptera: Curculionidae) on different growth stages of the weed Parthenium hysterophorus (Asteraceae) was evaluated in a glasshouse and field cages, and its field prevalence in Queensland, Australia was assessed. In the glasshouse, L. setosipennis reduced the plant height by 51%, number of leaves by 78%, flower production by 63% and plant biomass by 54% in rosette stage plants. Damage by L. setosipennis in rosette stage plants in the field cage reduced the primary stem height by 26% and flower production by 38%, but the impact on total plant height, basal stem width, root length, number of branches, root biomass and total plant biomass was not significant. In both glasshouse and field cages, the impact of L. setosipennis on preflowering and flowering stages of parthenium was not significant. L. setosipennis was recorded in 48% of the parthenium-infested sites (n=132) sampled and 16% of the sites showed high to very high levels of incidence. L. setosipennis was more prevalent on alluvial and black soils than on clay and sandy soils. L. setosipennis is a promising biocontrol agent for regions with prolonged dry periods and erratic rainfall pattern.