Invasive species: A global threat to trade and livelihoods

29Nairobi-Market

Copyright: CABI. Credit: Sven Torfinn, Panos Pictures

 

A new report supports the fact that invasive species have the potential to undermine global food security and sustainable development, a vital statement supported by Goal 15 of the Sustainable Development Goals which states that we need to: introduce measures to prevent the introduction and significantly reduce the impact of invasive alien species on land and water ecosystems and control or eradicate the priority species.

Invasive species are a plants, fungi or animals that are not native to a specific location (an introduced species) which spread and can cause damage to the environment, human economy or human health. If not managed sustainably, these invasive species often negatively impact natural biodiversity and ecosystems, and consequently, farmers’ livelihoods.

Rapid globalization and increased trade is compounding this problem. As agricultural and non-agricultural products move from one country to another, the risk of introducing invasive species to non-native regions is also increased.

Research carried out by Dean Paini (senior research scientist – CSIRO) on the Global threat to agriculture from invasive species was carried out across 124 countries. He found that 40 of the countries in the study had the possibility of being invaded by at least one of the 1,297 invasive pests reviewed. The research identified a correlation between the type of crops grown in a country, the level of trade with other countries and invasive pests present in trading countries. He reported that China and USA were the greatest potential sources of invasives species due to the scale of their agricultural production and high levels of trade with other countries.

The report found that countries in sub-Saharan Africa were more vulnerable to the impacts of invasive species. This is because of their less resilient farming systems and increased reliance on the natural ecosystem. Impacts of invasive species are mostly experienced by rural farmers but it’s also felt at the national economic level as agriculture contributes significantly to their Gross Domestic Product (GDP). It is therefore pertinent to understand the source, nature and method of spread of invasive species so that they can be prevented, mitigated or managed – if they’re already established.

We at CABI have launched a global initiative to raise awareness of the global threat of invasive species on food security, trade, sustainable development and rural livelihoods – see our dedicated website. CABI has over 100 years of scientific expertise and knowledge on invasive species and we are using this knowledge to help tackle the worst invasive species across Africa, Asia and Latin America. For instance, Opuntia stricta – an invasive cactus – has colonized vast grazing areas in Kenya, resulting in minimized grazing land and the death of livestock. We have therefore used our scientific expertise to help address this invasive by introducing a sap-sucking bug (Dactylopius opuntiae) which is known to feed only on Opuntia stricta without causing harm to any other native plant species. This bug has previously been successful in controlling Opuntia stricta in South Africa and has already started being effective in addressing the same issues in Kenya.

As sustainable agriculture and rural development is at the core of our work, we aim to tackle invasive species by improving the knowledge of local people on the different methods of preventing the arrival and spread of invasive species. We also want to support agencies responsible for early detection and eradication of invasive species as well as mitigate invasive species through sustainable measures. This will ensure that invasive species are addressed without causing further harm to the environment and livelihoods.

Malaria incidence and invasive plants – is there a link?

Mosquito

3.2 billion people are still at risk of getting malaria. Although progress has been made, if we are to achieve a 90% reduction in global malaria incidence and mortality by 2030 we must do more. Controlling invasive species may be part of the solution.

The path will not be easy. Mosquitoes are becoming increasingly resistant to pesticides – the front line of defence from malaria today. But there are other aspects we can consider, like the potential link between the incidence of malaria and invasive, non-native weeds.

It is widely known that mosquitoes need plant sugars, among other things, to survive and proliferate. Studies in Israel show that mosquitoes are much more likely (250 times more likely) to transmit malaria in areas rich in plant sugars. Could the improved management of invasive plants abundant on the African continent lead to a reduction in the incidence of malaria?

It is this question that brought together experts on malaria and plant invasions to a workshop in Kenya in December 2015, funded by the Bill & Melinda Gates Foundation. The broad objective of the workshop was to explore whether mosquitoes benefit from invasive plants and whether these plants have a positive influence on the rate of malaria transmission. The workshop also looked at whether invasive plants could be managed on a large scale.

Experts agreed that access to particular plant sugars increases the ability of Anopheles mosquitoes to transmit malaria. Although it is not known if invasive plants produce more sugars, they are more widespread and abundant than native plant species. In fact, many have the ability to invade semi-arid and arid areas, possibly increasing the prevalence of malaria in regions where mosquitoes could not survive in the past. Invasive plants also actively grow and produce flowers and fruit for longer periods than native plants, thereby extending the availability of plant sugars over longer periods than in the past. This may allow mosquitoes to retain high population numbers for much longer periods in invaded areas than in areas where there are no suitable invasive plants.

If there is an obvious link between invasive or weedy plants and Anopheles mosquitoes, can we significantly reduce the incidence of malaria by managing invasive plants?

There is no doubt that problematic plants can be controlled. Landowners, especially farmers, do it all time. The Government of South Africa allocates approximately US$120 million a year to control invasive plants, especially in water catchments, biodiversity hotspots and protected areas. It also invests in biological or natural control of invasive species. This is considered one of the most cost-effective management options, ideal for use in developing countries that do not necessarily have the resources for chemical or conventional control.

So, we can control weeds but would it reduce the incidence of malaria?

Lowering the abundance and density of any plant species favoured by Anopheles mosquitoes should lower malaria incidence. Managing many of these non-native weeds will also result in a multitude of other benefits for poor rural communities – like protecting farmland, for example.

This possible malaria-invasives linkage must be explored further. We need to do more research to fill in knowledge gaps. This includes looking at what plant species the Anopheles mosquitoes use within a given environment. Methodologies are being developed to see if rapid assessments of mosquito gut contents can provide information on what plant species they have been feeding on. We also need to look at the impact of removing certain species of invasive plants on mosquitoes. If we can compare mosquito abundance, longevity and ability to transmit malaria in areas where the invasive plant is dominant and where it is less dominant, we can build a fuller picture of the potential problem and solution.

Malaria is a terrible disease that still affects too many people. We must do all we can to understand the possible link between the incidence of malaria and invasive, non-native weeds. If a link can be found, management of invasive weeds could offer hope to many living under the threat of malaria.

By Dr Arne Witt, Coordinator, Invasive Species, CABI

For more information about CABI’s work managing invasive species, click here.

The impacts of invasive weeds in Chitwan National Park, Nepal

Mikania (Mikania micrantha) is a tropical vine which is native to the Americas. Often referred to as the ‘Mile-a-Minute Weed,’ mikania grows rapidly in areas of high rainfall and has become highly invasive in parts of Asia and the Pacific. Under the Convention on Biological Diversity, invasive species are defined as alien species that threaten native ecosystems, habitats or species and in Nepal, mikania and other invasive plants such as chromolaena (Chromolaena odorata) are becoming increasingly problematic within the Chitwan National Park (CNP). There, the plants are having a serious negative impact on native grasses, shrubs and the one-horned rhinoceros, and by implication, deer and tiger populations. They are also affecting the local people who reside in the buffer zones and rely on the park for fodder and other materials.

A rhino amongst chromolaena

A rhino amongst chromolaena

Rhinos

In a specific study on mikania, scientists from the National Trust for Nature Conservation, Nepal with support from CABI and the Zoological Society of London have found a significant negative relationship between high mikania coverage and the population of rhinos. This is because the mikania vine smothers the fodder plants that the rhinos feed on. This could also be influencing their movement to other areas of the park where they feed on resources and crops important to local people. This in turn may exacerbate conflict between the residents of the buffer zones and the wildlife in the area.

Deer and Tigers

The reduction in fodder plants is likely also to cause a mirrored decrease in the number of deer in the park. Deer feed on similar plants to the rhinos and the impact of mikania on native vegetation is therefore likely to affect their feeding behaviour in a comparable manner. As a result a decrease in deer numbers is likely to have a negative impact on tiger populations, with tiger numbers being directly related to the populations of their prey.

Local people

The residents of the buffer zones surrounding the CNP are known to rely on the core area of the park for resources such as fodder, which they use to feed their livestock. These residents recognise that fodder availability within the park has decreased and report that collecting materials now takes three times as long as it has in previous years to gather the same amount of fodder. Reduced fodder has been attributed to flooding of the park and the spread of invasive plant species. In particular, a high proportion of local residents report that mikania has a significant negative impact on the fodder growing in the park.

Sustainable control of mikania weed

CABI piloted using a rust fungus (Puccinia spegazzinii) as a classical biological control agent for mikania weed in India. This highly host specific and damaging pathogen has now been released in Papua New Guinea and Taiwan, where it is having a significant impact on the growth of the weed. The rust has recently been released on a number of other Pacific Islands, and could be considered for release in Nepal.

Ebola and IAS

A conversation with Dr Arne Witt

Dr Arne WittThe recent outbreak of Ebola virus disease in West Africa made headline news around the world. During the outbreak this fatal disease, endemic to parts of Central and West Africa, rapidly spread from Guinea, Sierra Leone, and Liberia to other countries in the region such as Nigeria, Mali and Senegal and then further afield to the USA, UK and Spain, mainly through infected health workers. This prompted decisive action from governments around the world and led to the implementation of strict controls at most national points of entry – as a result of this action and increased awareness, the further spread of this disease was effectively halted. No new infections have been reported for a number of months now but the cost has been significant – more than 10,000 people lost their lives, mainly in Guinea, Sierra Leone, and Liberia. However, it is highly probable that without significant interventions the costs could have been far higher. For example, the outbreak of bubonic plague or Black Death in Europe in the 17th century resulted in the death of 34 million people. The accidental introduction of potato blight, a crop disease which affects potatoes, from the Americas to Ireland in the mid-1800s contributed to the starvation of about 1 million people. Rinderpest, a disease affecting livestock was accidentally introduced to Africa from Asia in the late 19th century resulting in the deaths of, it is claimed, a third of the human population of what is now Ethiopia and two-thirds of the Maasai, an ethnic group of pastoralists in East Africa who are totally dependent on livestock. We may ask what Ebola, potato blight and rinderpest have in common – well obviously they have all have had a devastating impact on humanity but what binds them all together is that they are all INVASIVE ALIEN SPECIES (IAS). Fortunately, due to concerted efforts by a range of agencies rinderpest has been eradicated from the planet but as a result of increased trade, travel and tourism more and more species are being moved around the world and many are establishing and are continuing to have devastating impact on livelihoods. Read more of this post

Tackling Tutsan

Tutsan (Hypericum androsaemum) is invasive to New Zealand and Australia. Native to many countries throughout Europe and western parts of Asia, it is thought to have been introduced as a garden ornamental by acclimatisation societies in the 1800s due to its attractive yellow flower. Today, tutsan is a severe weed in several regions of New Zealand, most significantly affecting the Ruapehu District and Bay of Plenty region in the North Island. Over the last 20 years, tutsan has become an increasing problem in these regions; spreading throughout low fertility pastures and along roadsides. There is concern that tutsan has the potential to pose a significant conservation threat if it continues to spread at its current rate through scrub and native forest fringes.

Flowering tutsan plants growing in New Zealand (photo: Lizzie Rendell, 2011)

Flowering tutsan plants growing in New Zealand (photo: Lizzie Rendell, 2011)

Recent estimates indicate that around 150,000 ha of land in the Ruapehu district is affected by tutsan. Within the district, the annual cost of controlling the weed, and loss of farming profit amount to around $NZ1.2 million (£600,000), and loss of current land values is estimated at $NZ27 million (£13 million). Tutsan is a persistent weed for which there are no registered chemicals. Off-label herbicides are currently used in an attempt to limit its spread, but these are proving ineffective with stands typically reappearing several years later. The weed is unpalatable to stock and the topography of the region’s worst affected areas further limits the control methods possible. Read more of this post

Tuta absoluta on the rampage in Africa

Watch a new video illustrating the devastating impacts that Tuta absoluta is having on tomato yields, and what this means for farmers who rely on these crops for sustenance and income.

Dr Arne Witt, from CABI commented on the implications of Tuta absoluta infestation across Africa

“Tomatoes are one of the most widely cultivated crops in Africa and are grown in the backyards of almost every homestead across sub-Saharan Africa. This important cash crop and source of vitamins is now threatened by the recent arrival of the tomato leafminer, Tuta absoluta.

This Invasive Alien Species is rapidly moving down the African continent, having already decimated crops in Egypt, Ethiopia, Kenya and northern Tanzania. Growers are at their wits end as to how best they can control this pest and many have abandoned tomato growing altogether. The race is on to prevent its spread further south with various interventions planned to mitigate its impact in areas where it is already present.”

For more information on Tuta absoluta visit the Invasive Species Compendium and the Plantwise Knowledge Bank.

In the eye of the invasive species storm

17th September 2014 – Last weekend I experienced first-hand the impacts that invasive species can have. While carrying out research on an infestation of Opuntia Stricta in Laikipia, I felt something lodge itself in my eye. The following day I visited a specialist, as efforts to wash the thorn out of my eye had been unsuccessful.

They found that one of the very fine thorns, which are found on the fruit of the cactus, had become trapped in my eyelid and was scraping along the cornea. According to the specialist, another two days with the thorn in my eye would have resulted in me developing a corneal ulcer; which could have cost me my sight in that eye.

The thorns of Opuntia Stricta fruit are incredibly fine. So fine that the specialist was only able to detect it using microscopy equipment and dye. As well as being an unpleasant experience, this incident highlights the serious implications for those who live in areas which are infested with Opuntia Stricta, where many people would be unable to afford to seek medical help should they experience the same thing.

IMG_5125

Opuntia Stricta can also have a significant negative impact on livestock. If they get thorns in their eyes, there is no way for the owner to remove them. This could potentially result in loss of sight. Equally, it is not uncommon for goats to feed on the Opuntia fruit where the same thorns damage the goat’s stomach. This has been linked to the death of many animals in areas where this weed is prevalent as well as overgrazing in uninfected areas which is putting strain on pastoral land in these areas (Dodd, 1940).

While invasive species are often perceived as a biodiversity threat, they have a very real impact on the livelihoods and health of those who live in the areas in which they infest.

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