Air potato (Hoi) and the air potato leaf beetle

The origin of air potato is uncertain. Some believe that this species is native to both Asia and tropical Africa, while others believe it is only native to Asia and was introduced to Africa. Air potato is now widely naturalised in tropical and subtropical areas in the USA, the West Indies, and in the Pacific region. Air potato has become invasive in the Caribbean region, the southern USA, and on some Pacific Islands including Fiji, French Polynesia, Niue, Palau, Tonga, and Wallis and Futuna.

Edible varieties of air potato exist, particularly in India and West Africa, but the most common wild form is usually bitter and can be toxic if not prepared properly. Consequently, air potato was only ever used in the past as a famine food in the Pacific. It has been used extensively for traditional medicine in some parts of the world, but not the Pacific.

Impacts

Air potato foliage dies back in the winter/dry season, but quickly regrows from the tubers a few months later. Air potato can climb tall trees and block out sunlight below. Thick mats of air potato can quickly smother native vegetation causing native plant communities and other biodiversity to decline. These changes can mean that ecosystem functioning is impaired.  

Air potato can also have negative economic impacts. It can infest agricultural land, reducing crop yields. It can also clog waterways and damage infrastructure. The cost of controlling air potato can be significant.  

New areas can be colonised by air potato when the bulbils are spread around by flooding or storms. The bulbils can last a long time on the ground before sprouting and starting to grow.

Control methods

Since air potato grows on and becomes entangled with other plants, including native and beneficial plants, it is difficult to apply herbicide without also killing them. Manual removal is very time consuming. The plant can quickly resprout from the network of underground tubers and grow from cut vines and bulbils which can survive a long time, even if they are buried under soil. A natural enemy is available, a beetle (Liliocheris cheni), which has been used successfully to control air potato in Florida.

History in the Pacific

A leaf-feeding beetle was introduced to Niue in April 2024 to control air potato (Dioscorea bulbifera), also known locally as hoi.

This is a new natural enemy for the Pacific.

However, the beetle has been extensively studied in the United States and was first released in Florida and other southern states in 2012. There are plans to also introduce this beetle to other parts of the Pacific where air potato is a problem.

How would I recognise the beetle and what is its lifecycle?

The adults are 9mm long and bright red. To find them look on the underside of damaged leaves. Have your hand or a container ready to catch, as the adults tend to drop to the ground when disturbed. Adults are long-lived, lasting 5 months or longer.

You may also see big batches of yellow eggs on fresh leaves. The females each lay more than 1000 eggs in their lifetime. The brown larvae take about 4 days to hatch out and are usually found clustered together feeding at the tips of leaves.

After about 8 days the larvae are large enough to pupate in the soil for a couple of weeks. The whole lifecycle only takes about a month, so multiple generations can be achieved each year.

Don’t bother looking for the beetles in the winter/dry season when air potato dies back. Adults will be around then but hiding away.

How does it damage the air potato vines?

Adult beetles chew lots of round holes in the leaves. Larvae eat the leaf tissue, leaving the skeletonised veins of the leaf. Adults will also nibble on the bulbils, but both prefer leaves especially the fresh ones. This stops the vines from growing as large.

Will it attack other plants?

No, the beetle only feeds on Dioscorea bulbifera, but all varieties of air potato will be susceptible to the beetle.

How effective is it?

In Florida, these beetles have resulted in a massive reduction in leaves, bulbils and spread of the vine. They have proven to be an effective and low-cost way of controlling and reducing air potato vines and are considered a major success.

How can I get the most out of it?

The adults can fly and will spread around over time slowly by themselves. However, if it is necessary to speed up dispersal the beetles could be collected at sites where they are abundant and moved to where they are needed. They are safe to touch, and don’t bite. If necessary, the beetles can be kept in a container with fresh leaves for a few days, but the sooner they can be released the better.

Are there other natural enemies for this weed?

A beetle (Liliocheris egena) that feeds on the bulbils of air potato has recently been approved for release in Florida. It is expected to complement the leaf beetle and achieve even greater suppression of air potato. The bulbil beetle could be considered for the Pacific, if necessary, in the future.