Finding a biocontrol for Himalayan raspberry
Yellow Himalayan raspberry is a major threat to native Hawaiian forests. A single plant can grow into a 4m tall impenetrable thicket, and its aggressive growth and rapid colonization enables it to outcompete native species. Current control methods are both labour intensive and costly. The aim of this project is to find biological control agents (both arthropod and fungal) from the plant’s native Indian and/or Chinese region of the Himalayas to control its spread in the Hawaiian introduced range.
So, what’s the problem
Rubus ellipticus var. obcordatus, or yellow Himalayan raspberry, is regarded as one of the world’s 100 worst invasive species and is a major threat to native Hawaiian forests. A single plant can grow into a 4m tall impenetrable thicket, with its main stem exceeding 10cm thick. Its prickles and sturdy stems make it extremely unpleasant for livestock and humans alike.
Native to the tropical and subtropical Himalayan region (ie India, China), yellow Himalayan raspberry was first introduced to Hawai’i in the early 60s and began to naturalize in the vicinity of Volcano in Hawai’i. It has been spread by birds and humans to the outskirts of Hilo and as far as Laupahoehoe. In addition to being a weed of pastures and disturbed areas, it demonstrates an alarming ability to deeply invade pristine wet forests such as the Olaa Tract of Hawai’i Volcanoes National Park.
Its aggressive growth and rapid colonization enables yellow Himalayan raspberry to outcompete native species, and its impenetrable monocultures and the extensive root system are degrading existing pristine natural habitats. Its method of seed dispersal also allows it to spread rapidly and current control methods are both labour intensive and costly.
What is this project doing?
To remedy this situation, a team from CABI is aiming to find potential biological control agents (both insect or fungal) from the Indian or Chinese region of the Himalayas which are damaging to Himalayan raspberry, but don’t attack other plant species. An initial scoping study evaluated the potential for using biological control for yellow Himalayan raspberry. In parallel we carried out extensive reviews of natural enemies recorded on yellow Himalayan raspberry in the plant’s area of origin, using published literature, CABI databases and our unique herbarium data.
The team conducted several surveys in the Indian region of the Himalayas, first in collaboration with the National Bureau of Plant Genetic Resources (NBPGR) and later with the National Bureau of Agricultural Insect Resources (NBAIR), to assess and collect potential agents. Specimens of collected species were sent for identification at the appropriate Indian depositories: New Delhi and Bangalor (insects) and Mau (fungal pathogens). Following formal identification we applied for and were granted with an official license to export four prioritized insect species to CABI’s quarantine facility in the UK in order for us to undertake any potential further research. An initial survey to compile comparative data of natural enemies was also conducted in China.
The first survey for natural enemies of Rubus ellipticus var. obcordatus was conducted in the Indian Himalayas in 2012. The plant is prevalent in a variety of habitats here including forests, grasslands and fringes of high altitude meadows. The team sampled distinct populations and collected numerous invertebrate and fungal species, some of which were visibly highly damaging to the plants.
In 2014/15 two further surveys were conducted in the same region and, additionally, the Nilgiri Hills of southern India. Based on formal identification by Indian taxonomists, field observations and literature searches, seven insect species, including a leaf rolling moth and five genera of a beetle species, as well as a rust and a leafspot fungus were prioritized for further assessment as biocontrol agents. In 2016 an export permit to the UK was officially granted by the Indian authorities for four of the insects, but as yet none of these has been exported. The survey conducted in the Chinese provinces of Yunnan, Guizhou and Sichuan in 2014 prioritized two beetle species, a sawfly, a tortricid moth as well as a rust and a leafspot pathogen as potential biocontrol agents. Further evaluation of all agents has yet to be undertaken.
In 2018/19, collaborations in India will be re-engaged with the aim to conduct further surveys to export prioritised species for host specificity testing against key Hawaiian Rubus spp. Other insects and pathogens collected will be evaluated for potential, as appropriate.