In November, MWLR and our partners in Vanuatu released the pico beetle (Leptinotarsa undecimlineata) to tackle the spread of the invasive weed prickly solanum (Solanum torvum), known as pico weed in Vanuatu. This follows on from the successful release of the hibiscus bur lace bug (Haedus vicarius) in July last year, all part of a larger and ongoing effort to restore pasture lands that have been overrun by invasive weeds in Vanuatu.
Image: pico beetles.
Prickly solanum is a thorny shrub or small tree with broad, hairy leaves. It overtops most herbs, grasses, and shrubs, limiting the growth of other species. The weed has long posed a serious problem for farmers, particularly in cattle-grazing regions, where its thorny structure and toxicity make it unsuitable as fodder.
The plant’s rapid spread has forced some farmers to reduce livestock numbers or abandon parts of their grazing land. The weed produces attractive berries that are rapidly dispersed by birds, and in some Pacific countries these berries provide habitat for pests such as fruit flies, which damage valuable crops, compounding the challenges faced by local farmers.
“Prickly solanum has created a serious challenge for our livestock sector,” said Biosecurity Vanuatu’s Senior Plant Health Officer Leisongi Bulesulu. “Farmers have struggled with limited grazing land, and we’ve had to explore alternative methods to control its spread. The introduction of the pico beetle is a critical part of our long-term strategy to restore our pastures.”
The pico beetle, which is native to Mexico, Central America, and northern Colombia, and is also found on some Caribbean islands, including Jamaica, is the first natural enemy ever released globally to target prickly solanum. Both the adult beetles and their larvae feed on the leaves, effectively stripping the plant and allowing pasture to regenerate.
A team from MWLR delivered the beetles to Biosecurity Vanuatu on Efate in early November last year after spending 5 years studying the beetle, determining its suitability as a biocontrol agent, and assessing the potential risks of releasing it. Another team delivered beetles to the Vanuatu Agricultural Research and Technical Centre (VARTC) on Santo a few weeks later.
“This release is of great significance for Vanuatu, where it was recently estimated that 34% of grazing land is lost to weeds. The most problematic pasture weed is prickly solanum, which was ranked the worst or second worst weed on 81% of farms,” said Quentin Paynter, who leads the Vanuatu Pasture Weeds Programme. “The release of the pico beetle means a natural enemy has now been released for three of the four worst pasture weeds in Vanuatu.”
This release builds on previous introductions, including the nail grass psyllid (Heteropsylla spinulosa) and the hibiscus bur lace bug, which were released on Efate in July, with the lace bug also being released on Santo at the same time as the pico beetles in November. Work on natural enemies for wild peanut (Senna spp.) is still in progress.
“Invasive weeds like hibiscus bur and prickly solanum have devastated grazing lands across Vanuatu. Farmers have faced reduced livestock numbers, lower yields, and escalating costs for chemical or manual weed removal. The introduction of natural enemies is a game-changer, offering a sustainable, cost-effective solution to these challenges,” said Steglar Tabi Aga, CEO of VARTC. By allowing the natural enemy to control the weed’s growth, it is hoped the beetles will significantly reduce the weed’s presence over time, providing much-needed relief to farmers and allowing pasture cover to thrive once again.
“When in abundant numbers the pico beetle can completely defoliate and debark the prickly solanum weed, killing it. It is also important to note that this beetle only affects prickly solanum in Jamaica, where it has not been recorded affecting any crops of economic importance. Its safety has also been demonstrated in laboratory tests. We’re optimistic that this novel natural enemy will significantly reduce the weed’s presence and allow pastures to recover over time,” said Quentin.
Following the release, researchers, and staff at Biosecurity Vanuatu and VARTC are closely monitoring the beetles’ establishment and effectiveness in controlling prickly solanum. If successful, the project could serve as a model for other Pacific nations facing similar invasive species challenges. Sustainable biocontrol solutions strengthen the region’s resilience to natural disasters, such as the recent devastating earthquake and cyclones in Vanuatu, and to the impacts of climate change.
The Vanuatu Pasture Weeds project is a part of the Pacific Regional Invasive Species Management Support Service’s (PRISMSS) Natural Enemies – Natural Solutions programme. PRISMSS is administered by the Secretariat of the Pacific Regional Environment Programme. The Vanuatu Pasture Weeds project is funded by New Zealand’s Ministry of Foreign Affairs and Trade.
