How widespread is Parthenium hysterophorus and its biological control agent Zygogramma bicolorata in South Asia?

Parthenium hysterophorus is a weed of global significance causing severe economic, environmental, human and animal health problems in Asia, Africa, Australia and the Pacific. In South Asia, P. hysterophorus occurs in India, Pakistan, Sri Lanka, Bangladesh and Nepal. A host-specific leaf-feeding beetle Zygogramma bicolorata from Mexico was introduced into India in 1984, as a biological control agent for P. hysterophorus. In this study, a GIS-based distribution map of P. hysterophorus and its biological control agent Z. bicolorata in South Asia based on meta-analysis is presented. The map highlights the limited published information on P. hysterophorus incidence in many of the states and territories in India, as well as in neighbouring Bangladesh, Bhutan, Nepal and Pakistan. Incidence of Z. bicolorata was recorded as three distinct clusters, covering many states in India. In Pakistan, Z. bicolorata was recorded in the Punjab region bordering India. A CLIMEX model based on the current distribution of Z. bicolorata in India suggests that the geographic range of this agent in India and Pakistan can extend to other P. hysterophorus-infested areas in the region. The CLIMEX model also suggests that all of Bangladesh and Sri Lanka, and parts of Nepal are climatically suitable for Z. bicolorata.

Overcoming barriers to the successful implementation of a classical biological control strategy for the exotic invasive weed Mikania micrantha in the Asia-Pacific region

Mikania micrantha (Asteraceae) commonly known as mikania, is a major invasive alien plant (IAP) in the tropical humid agricultural and forest zones of the Asia-Pacific region. This fast-growing Neotropical vine is able to smother plants in agricultural ecosystems, agroforestry and natural habitats, reducing productivity and biodiversity. Fungal pathogens were first investigated for the classical biological control of this weed in 1996. This resulted in the selection and screening of the highly host-specific and damaging rust pathogen, Puccinia spegazzinii (Pucciniales). It was first released in India and China in 2005/6, although it is not believed to have established. Since then, it has been released successfully in Taiwan, Papua New Guinea (PNG), Fiji and most recently Vanuatu. The rust has established and is spreading rapidly after applying lessons learned from the first releases on the best rust pathotype and release strategy. In PNG, direct monitoring of vegetation change has demonstrated that the rust is having a significant impact on M. micrantha, with no unpredicted non-target impacts. Despite this, the authorities in many countries where mikania is a problem remain cautious about releasing the rust. In Western Samoa, introduction of the rust was not pursued because of a conflict of interest, and the perception that mikania suppresses even worse weeds. For some, ‘pathophobia’ is still a major obstacle. In Indonesia, where insects for weed CBC have been introduced, pathogens will currently not be considered. In other countries such as Bhutan and Myanmar, there are no baseline data on the presence and impact of IAPs and, with no history of CBC, no institutional framework for implementing this approach. Malaysia has a well-developed framework, but capacity needs to be built in the country. Overall, it remains critical to have champions at decision making levels. Hence, even with an effective ‘off-the-shelf’ agent available, implementation of mikania CBC still requires significant inputs tailored to the countries’ specific needs.