Classical biological control of exotic weeds

Abstract

Biological invasion has become a serious ecological and economic concern in the international community as well as in China. Invasive exotic plants have caused vast damage to the biodiversity and the economy in China. Classical biological control of weed aims to suppress and achieve long term regulation of weed populations by introducing host-specific natural enemies from the native range of the weed. It is a self-sustainable and self-regulating management approach widely used in the world, while being systematically explored in China since the 1980's. This paper reviews the current status, main challenges and prospect of classical biological control of weeds in the world, highlighting some important and successful cases, and discusses the priorities, recent development and successes, and main challenges in China. More than 70 countries have developed weed biological control programs. The U.S.A., Australia, South Africa, Canada and New Zealand have actively been using more agent species against target weeds than the other countries. There have been at least 63 families 369 species of invertebrates and fungi utilized against 133 species of target weeds belonging mainly to the plant families of Astereae, Cactaceae and Mimosaceae. One case reviewed in the paper has demonstrated to be successful for more than 100 years in biological control of weed history. And more successful cases are recognized as examples in controlling exotic weeds by classical biological control, such as Opuntia inermis O. stricta, Hypericum perforatum, Alternanthera philoxeroides, Salvinia molesta, Hydrilla verticilla, Chondrilla juncea etc.. Biological control of Eichhornia crassipes remains the most difficult and important program in the world.Classical biological control of weeds began to be systematically studied and practiced since the mid 1980's in China, although there had been attempts and even community campaigns of using fungus as bioherbicides in the 1960's. So far, 14 species of biocontrol agents have been introduced to control 4 species of target weeds, viz. Eupatorium adenophorum, Alternanthera philoxeroides, Ambrosia spp. and Eichhornia crassipes. The introduction of Agasicles hygrophila from USDA to control Alternanthera philoxeroides has been by far the most successful in China. Through collaboration with USA and Canada by the Chinese Academy of Agricultural Sciences, 23 species of insects and fungi were found in China and exported to North America for the control of Euphorbia esula, Tamarix spp., Cirsium arvense, Myriophyllum spicatum,Hydrilla verticillata,Trapa natans, Polygonum perfoliatum. Introducing Agasicles hygrophila to control Alternanthera philoxeroides is by far the most successful case in China. Classical biological control as a promising approach for the long-term control of invasive exotic weeds is faced with many challenges in China, such as the development of the science, research in host specificity testing, biosafety issues, funding for the long-term programs, just to name a few. With its rich and unique biodiversity, China needs to develop and implement a sound management system to conserve and protect the biodiversity. Classical biological control against invasive exotic weeds will, if given a priority and support, play a promising and important role in the protection and utilization of the biodiversity.