Lace Bug Release In Vanuatu To Combat The Invasive Hibiscus Bur

Researchers from Manaaki Whenua – Landcare Research (MWLR) are undertaking the first global release of a lace bug species in Vanuatu at the end of July to combat the invasive hibiscus bur (Urena lobata ) shrub.

The hibiscus bur lace bug (Haedus vicarius) is a leaf-feeding insect native to Malaysia, and as a natural enemy of hibiscus bur has shown great promise in damaging and potentially controlling this invasive, and destructive pasture weed.

Manaaki Whenua has been working to develop novel natural enemies for invasive pasture weeds in Vanuatu since 2018 in its role as project lead for the international Pacific Regional Invasive Species Management Support Service (PRISMSS) Natural Enemies – Natural Solutions (NENS) project. “Hibiscus bur was a focus because it infests pastures, reducing grazing for cattle,” says senior researcher Dr Quentin Paynter who leads the NENS Vanuatu Weeds Programme.

“Vanuatu has been a leader in the Pacific for adopting NENS and the lace bug will be the 12th natural enemy to be introduced to control invasive weeds in the country, and the sixth species to be released as part of the current NENS project,” said Quentin. “What sets this release apart is that it is the first agent in Vanuatu for a ‘novel’ target weed that has never previously been targeted for control using natural enemies anywhere else in the world.”

In an effort that highlights the importance of international collaboration in addressing environmental challenges, the team from Manaaki Whenua will be in Vanuatu next week. The team will oversee the first release, supported by local partner Biosecurity Vanuatu, who will, over the coming months, continue mass rearing and releasing the lace bug throughout Efate and on other islands where hibiscus bur infests pastures.

“We are very much looking forward to establishing this agent in Vanuatu,” says Acting Principal Biosecurity Officer, Biosecurity Vanuatu Leisongi Bulesulu. “Hibiscus bur is a real problem for some farmers because it is hard to remove manually and most farmers here are not able to use chemicals.

“The only other option is the use of natural enemies to reduce the population of Hibiscus burr in their paddocks or garden areas.” It is estimated that a third of the pastures in Vanuatu are currently lost to pasture weeds, of which three species (all targets of the current NENS programme) are most significant: pico (Solanum torvum,) wild peanut (Senna tora), and hibiscus bur.

The hibiscus bur lace bug damages the plant by inserting its needle-like mouthparts into the leaf tissue and extracting fluids leading to yellowing and death when severe. “In the native range of the lace bug, it has been reported to cause extensive defoliation of hibiscus bur, so we believe it will be effective.” says Quentin. “Ongoing monitoring of the impact of the lace bug in Vanuatu will be crucial to evaluate its effectiveness.”

“Our colleagues at Biosecurity Vanuatu will assess the bug’s ability to disperse and establish in new areas and use this information to plan further redistribution efforts.”

The hibiscus bur, characterised by its pink hibiscus-like flowers and prickly burs with hooked spines which easily attach to animal fur and people’s clothing, enabling the weed to spread, originates from Asia and is also possibly native to parts of Africa. It has spread globally, often introduced accidentally or as a fibre crop. It now forms dense, monospecific stands that choke out native vegetation and reduce pasturelands.

Using the natural enemy of a plant is a promising alternative to herbicides or mechanical removal, which are often costly and labour-intensive. Herbicides can be expensive and pose environmental risks, while mechanical control requires significant investment in equipment. “Hand-pulling weeds is impractical for large-scale infestations,” says Quentin. “The lace bug, however, offers a sustainable solution by naturally targeting and damaging the hibiscus bur.”

Extensive trials have been done on the lace bug and the insects have shown no potential impact on non-target species.

Manaaki Whenua senior technician Stephanie Morton, who researched the host specificity of the lace bug, says testing has shown the lace bug is highly host specific and likely to only attack hibiscus bur in field conditions. “We also saw the lace bug could only reproduce successfully and persist on hibiscus bur.”

Manaaki Whenua’s NENS programme falls under the Pacific Regional Invasive Species Management Support Service (PRISMSS) which is supported by NZ’s Ministry for Foreign Affairs and Trade, and the GEF-6 Regional Invasives Programme.

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