Towards understanding field performance of introduced insect agents on Parthenium hysterophorus in South Africa

Towards understanding field performance of introduced insect agents on Parthenium hysterophorus in South Africa
Lorraine W. STRATHIE, Frank Chidawanyika, Sakhi Sambo, Milly Gareeb
Agricultural Research Council – Plant Protection Research Institute, Private Bag X6006, Hilton 3245, South Africa 

Successful management of Parthenium hysterophorus (Asteraceae; known as parthenium or famine weed) in various invaded environments requires a suite of natural enemies. Each agent has unique attributes and limitations that contribute to levels of success that may be achieved. In recent years, three imported insect agents (Listronotus setosipennis (Coleoptera: Curculionidae), Zygogramma bicolorata (Coleoptera: Chrysomelidae) and Smicronyx lutulentus (Coleoptera: Curculionidae)) have been introduced into multiple sites within subtropical regions of South Africa that are severely invaded by parthenium. Highly variable establishment and field performance is apparent, likely due to a combination of intrinsic and external factors. Despite several desirable biological characteristics and reasonable field establishment of the endophagous stem-boring weevil L. setosipennis, distribution is localised. Field evidence of temperatures that reach critical or lethal limits, together with demonstrated variability in the thermal tolerance of the defoliating beetle Z. bicolorata of different ages, feeding status and thermal pre-treatments under laboratory conditions, suggest some causative influences on its field establishment. Resultant implications for improved biological control of parthenium, and the need for additional complementary agents that can address local limiting factors, are discussed.