Malaria incidence and invasive plants – is there a link?


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.

100 invasive weed factsheets project and my development bursary

Development bursary group pic

Workshop attendees: Invasive weed factsheet development. Nairobi, Kenya. February 2016.


Keen to meet colleagues and external partners in Kenya, and to learn new skills, I applied to CABI’s annual staff Development Bursary in 2015. Successful, I journeyed to Nairobi in February 2016 where I assisted with a workshop focussed on developing factsheets on invasive weed identification, management and control. These factsheets will ultimately help improve the livelihoods of farmers by reducing crop losses.

Who am I?

I am Kate Dey, a Content Editor for CABI’s Invasive Species Compendium (ISC) (kneeling front, right of image above). Sitting in the small compendia office on the second floor at Wallingford HQ, UK, I spend the majority of my time commissioning and editing datasheets. I also update distribution and pest records for the Crop Protection Compendium (CPC) and help manage the @CABI_Invasives Twitter account.

Leading up to my bursary application

In October 2015, I was asked to assist with a project which is part of an initiative known internally as the Invasives Big Push. The aim of this initiative is to stop the world’s worst invasive species undermining the livelihoods of 50 million farming families. To help achieve this aim, the project’s focus was to produce 100 factsheets on invasive weeds for East Africa (Kenya, Tanzania, Ethiopia, Malawi, Rwanda and Uganda) and Southeast Asia (Myanmar, Thailand and Vietnam) with the overarching theme of empowering farmers by providing them with clear and practical information on weed management and control. This exciting project is a collaborative one which involves CABI’s Invasives and Plantwise teams, and external partners, working together.

So I got stuck in, assisting with the prioritisation of species to be covered. They were largely prioritised by taking into account: impact on major crops (mainly maize and rice); number of countries affected by weed; and amount of information CABI already has (largely looking at the ISC and CPC) which could be repurposed and shared more widely.

I proceeded to create the first drafts, editing information from the Compendia so that it was compatible with the factsheet format required by CABI’s Plantwise Knowledge Bank (PWKB) – an online pest information resource on which the factsheets were to be hosted. Making this information available via the PWKB means it will be more readily available to extension workers who can use it to give effective advice to farmers struggling with weed infestations.

More specifically, I helped draft the first few species-specific Pest Management Decision Guides (PMDGs) which hold clear, practical, country-specific advice on pest management and control, and support Integrated Pest Management principles (IPM). These are usually produced by Plantwise but on this occasion their creation was the responsibility of the Invasives Big Push Team because of the focus on invasive weeds. Hence, Plantwise were instrumental in the creation of these factsheets, providing us with useful training and ongoing support.

The second type of factsheets produced was species-specific descriptive factsheets. The creation of these would fulfil the objective to repurpose and disseminate information from weed ID guides, produced by CABI employee Arne Witt. Along with the PMDGs, these were to be developed at two workshops in Kenya and one in Bangkok, making them country-specific in the process. Keen to be part of the development phase and to see what would become of our drafts, I applied for the development bursary in December 2015.

The workshop

I was lucky enough to attend the first four day workshop in Nairobi, Kenya, where the drafted factsheets would be developed. Attendees included specialists in weed ecology and control from a variety of research organisations and universities, and had travelled from Tanzania (2 people), Ethiopia (6 people) and within Kenya itself (6 people).

Day 1


Arne Witt, talking about impacts invasive alien species on crops

Participants were welcomed and introduced, and opening presentations were given, covering: background to the Invasives Big Push and Plantwise initiatives (by Marion Seier); introduction to factsheets and PWKB (by me); impacts of invasive alien species on crop production, and introduction to integrated pest management (IPM) principles (by Arne Witt).

Before beginning factsheet development, we needed to ask each country group what weeds they thought we should focus on. Participants were asked to complete a prioritisation table which would enable them to rank the importance of weeds in their country. It contained criteria such as area affected, crops affected, health impacts and ease of control. Species selected were those ranked 1-10 by at least two countries, luckily resulting in a large cross-over with the countries we had previously prioritised. We then started reviewing the country-specific descriptive factsheets together, asking participants to look over the drafts (some created beforehand and some created during the workshop itself) and confirm the most important common local names for each species.

Day 2

The descriptive factsheets were completed in the morning, before further presentations were given on PMDG writing (by René Eschen) and international pesticide agreements (by Sarah Thomas). We then started discussing how to write the PMDGs. Importantly, the information needed to: promote the use of preventative methods as the first line of defence; provide monitoring guidance so an infestation could be identified early on; and promote the use of the least harmful control methods if an infestation is present (i.e. non-chemical control). If these methods proved ineffective, it was essential to provide information on how to correctly use potentially harmful control methods (i.e. pesticides) safely and effectively.

The first step was to talk through the content of an existing PMDG together, in order to gain an understanding of what should go in the Prevention, Monitoring and Direct Control columns, and what restriction and limitation information was essential to include along with pesticide recommendations. We then reformed into country groups and had a go at creating a PMDG from scratch (for Parthenium hysterophorus, a weed that can not only reduce crop yields by over 90% but also poses a serious health risk to people and livestock).

After completing this task, we joined together again and listened to a representative from each country group present the PMDG they had produced. Content was debated and discussed, helping everyone further their understanding of the information required and providing inspiration by comparing differences and similarities. We then started on PMDGs for the rest of the prioritised species.

Days 3 & 4


Sarah Thomas, assisting with PMDG development

During the final days, PMDG drafts were reviewed, refined and added to. Along with Marion, René, Arne, and Sarah, I sat with the participants, answering their questions on what information was required, where it should be placed and how to make it clear. We assisted with entering the text into the forms and helped look up pesticide information; checking whether they were on Plantwise’s Red List (containing internationally restricted/not to be used pesticides) and on the nationally approved lists.

Some PMDGs were placed on the walls so groups could gain ideas from each other’s factsheets, particularly since many management and control methods would be the same for each country. For this reason also, PMDGs were rotated around the groups, so that as the factsheets were circulated participants added to and edited what a country group before them had written, thereby maximising efficiency. By the final day 18 weed species had been covered, and 33 PMDGs and 30 descriptive factsheets had been produced – a fantastic outcome which was thanks to an engaging, friendly and hard-working group.

What will happen next?

The factsheets will now need to pass through a review process, whereby content will be edited by Plantwise and a weed specialist will validate the information. The final versions will be uploaded the PWKB, a key resource for extension workers, called Plant Doctors, who advise farmers on what action to take when a pest is impacting on their crop. Farmers bring their affected crop along to a local Plant Clinic where the Plant Doctor makes a diagnosis (find out more at The factsheets will provide Plant Doctors with the tools they need to help farmers loose less of what they grow to crop weeds, increasing the amount of food they can sell and eat and ultimately improving their livelihoods.

What did I get out of it?

Firstly, I really enjoyed working with such dedicated and passionate participants, listening to them talk about their research and experience and how much they care about helping farmers. Many of them had farming backgrounds, and/or had close friends and family who were farmers, so they had a good understanding of the challenges they face.

Two particular subjects that we discussed with participants stuck with me; firstly, the presence and growing dominance of women in farming businesses. More and more men are leaving farms to go to the cities and towns to find jobs, which is not surprising when you consider the back-breaking work, high running costs, unpredictable outputs and slim profit margins. 60% of pre-harvest labour in Africa is hand weeding, mostly by women and children (who often have to leave school during peak weeding periods). 100 million women in Africa spend 20 billion hours weeding every year. Secondly, the extent to which pesticides are used unsafely and ineffectively is huge, with many farmers developing health problems from incorrect use, such as not wearing protective clothing or using too high a concentration. More than one participant mentioned that many farmers who use pesticides in Africa don’t eat the crops they spray because even they aren’t sure that they’re safe. Furthermore, there was a story of one farmer not being able to get their beans to market, consequently feeding those beans to their livestock, and their livestock dying from poisoning as a result.

It was also great to make new friendships with CABI staff members who I may not have been able to meet through my usual line of work. It was a really nice experience walking into a CABI office I’d never been to but still feeling welcome and a sense of familiarity. We’re often reminded of the ‘One CABI’ ethos at work but those words mean so much more when you actually experience it. It was not just lovely to meet Kenyan staff, but also to work with Marion, René and Sarah from Egham, UK.


Overall, it was fantastic to be part of a project with the purpose of improving people’s lives. These factsheets will directly help farmers to more effectively manage and control invasive weeds, improving yields and so resulting in more food and income for their families. The workshop experience was a reminder that there is still more work that needs to be done, but that by working together we can really make a difference.

New in January and February 2016 from the ISC

In January and February 2016 the following datasheets were published on CABI’s Invasive Species Compendium (ISC). You can explore the open-access ISC here:

By Franz Xaver (Own work) [CC BY-SA 3.0 ( or GFDL (], via Wikimedia Commons

1. Agropyron cristatum

Agropyron cristatum (crested wheatgrass)

A. cristatum is a resilient and long-lived perennial grass with stems that are 20-70 cm long and with finely-branched deep roots that extend to a depth of 1 m. It is able to grow in a wide range of habitats making it a very effective invader. Its native range is the Russian and Siberian steppes but it is now present in the North American prairies where it was planted in the 20th century to reseed abandoned cropland. It has since invaded vast areas of rangeland across the upper USA and southern Canada where it outcompetes native vegetation, altering soil chemical properties as a result.

By Homer Edward Price (Bushy-Bluestem Uploaded by Amada44) [CC BY 2.0 (], via Wikimedia Commons

2. Andropogon glomeratus

Andropogon glomeratus (bushy bluestem)

A. glomeratus is another invasive perennial grass, but is taller than A. cristatum, with stems that can be 1.5 m in height. It is a popular ornamental because of its bushy/tufted appearance and is consequently found outside of its native range of southeastern USA, Mexico and parts of Central Mexico and the Caribbean. Introduced to Hawaii, USA, where it is considered a noxious weed, it is outcompeting the small, native and endemic shrub Vaccinium reticulatum. A. glomeratus can also change fire regimes as it is highly flammable. This can promote invasion by other non-native species.

By scott.zona (Flickr: Atriplex semibaccata) [CC BY 2.0 (], via Wikimedia Commons

3. Atriplex semibaccata

Atriplex semibaccat (Australian saltbush)

A. semibaccata is a perennial shrub which can grow up to 80 cm tall and is drought and salt-tolerant. It is a valued fodder crop but it can form dense and fire retardant groundcover that displaces native species. In Hawaii, USA, it is impacting on a number of endangered plants such as Panicum niihauense, along with other invasive species. In California, USA, it is competing with Verbesina dissita which is endangered and restricted to the Laguna Beach area of Orange County.

I, Hugo.arg [GFDL (, CC-BY-SA-3.0 ( or CC BY-SA 2.5-2.0-1.0 (], via Wikimedia Commons

4. Phleum pratense

Phleum pratens (Timothy grass)

P. pratense is a (yet another!) invasive perennial grass which can grow up to 1.5 m tall and spreads vigorously. It is an important forage grass, native to Europe and Asia, which can alter native plant communities by forming monocultures (vegetation consisting of the same species). Its seed is considered a contaminant of grass and other seed lots in the eastern US states of Delaware, Maryland, New Hampshire, New Jersey, Pennsylvania, Virginia and West Virginia, thus reducing seed lot quality and price. P. pratense is also a host to diseases, such as ergot (Claviceps purpurea), that are serious pathogens of cereal crops.

By Walter Siegmund (Own work) [GFDL ( or CC BY-SA 3.0 (], via Wikimedia Commons

5. Rubus parviflorus

Rubus parviflorus (thimbleberry)

R. parviflorus is a deciduous, perennial raspberry species which produces edible fruits and can act as a soil stabiliser. Its fruits are eaten by the indigenous peoples of North America who also use parts of the plant to treat a wide variety of ailments such as stomach ache and diarrhoea. It is native to North America and Canada, however it has been recorded as invasive in British Columbia, Canada, due to the fact it can outcompete seedlings of economically important conifer species. It has also been recorded as invasive in parts of Europe.

  1. Agropyron cristatum by Franz Xaver (Own work) [CC BY-SA 3.0 ( or GFDL (, via Wikimedia Commons
  2. Andropogon glomeratus by Homer Edward Price (Bushy-Bluestem  Uploaded by Amada44) [CC BY 2.0 (, via Wikimedia Commons
  3. Atriplex semibaccata by scott.zona (Flickr: Atriplex semibaccata) [CC BY 2.0 (, via Wikimedia Commons
  4. Phleum pratense by I, Hugo.arg [GFDL (, CC-BY-SA-3.0 ( or CC BY-SA 2.5-2.0-1.0 (, via Wikimedia Commons
  5. Rubus parviflorus by Walter Siegmund (Own work) [GFDL ( or CC BY-SA 3.0 (, via Wikimedia Commons

New in November and December 2015 from the ISC

In November and December 2015 the following datasheets were published on CABI’s Invasive Species Compendium (ISC). You can explore the open-access ISC here:

By peganum from Henfield, England (Cotoneaster horizontalis) [CC BY-SA 2.0 (], via Wikimedia Commons

1. Cotoneaster horizontalis

Cotoneaster horizontalis (wall-spray)

C. horizontalis is a woody, perennial, deciduous or semi-evergreen shrub with horizontally spreading branches, native to parts of China. It is an attractive garden plant with bright red berries which is the main cause for its widespread introduction across the world. In addition to keen gardeners, seeds of this plant are spread easily by birds. Unfortunately, it invades chalk grasslands (such as those of the South Downs in the UK), reducing species richness and diversity.

By Liné1 (Picture taken with my IXUS 800 IS) [GFDL ( or CC BY-SA 3.0 (], via Wikimedia Commons

2. Cyperus papyrus

Cyperus papyrus (papyrus)

C. papyrus is a tall (up to 5 m), fast-growing, aquatic perennial sedge native to North Africa, well-known as being a source material for the making of paper (papyrus). Plumes of thread-like stems at the top of the plant make it particularly attractive and have resulted in its use as an ornamental plant and consequently its introduction to other countries. It can anchor itself in water via shallow roots or floats freely in clumps, facilitating its spread. The dense and extensive stands it can form can impede the flow of waterways and displace native species. It can reduce the amount of light that reaches submerged plants and can impact on habitats of wetland bird species.

Myroxylon balsamum (Peru balsam)

M. balsamum is a large tree of tropical America (40-45 m tall and 1 m wide) which produces lots of small whitish flowers and winged seedpods. Providing valuable timber and balsam resin, it has been widely introduced. It can form dense stands and can therefore outcompete native species by shading them. Characteristics which make it such a strong competitor include its large size, capacity for prolific seed production and ability to tolerate a wide range of light conditions. It is particularly problematic in Sri Lanka where native species can tolerate less varied light conditions and where natural enemies, such as diseases and insects, are absent.

By Meneerke bloem (Own work) [GFDL ( or CC BY-SA 3.0 (], via Wikimedia Commons

3. Persicaria wallichii

Persicaria wallichii (Himalayan knotweed)

P. wallichii is a shrubby perennial herb that originates from the temperate western regions of Asia and the Indian subcontinent. It is reported as invasive in its native range of India and its non-native range of Belgium and the UK. In the USA, it can promote the erosion of river banks where it pushes out native stabilizing species, colonizes large areas, but then dies back in the winter. Furthermore, the dense mats of leaf litter it produces can prevent the germination of native species. It can compete for resources with trees and reduce shade along rivers and streams by displacing native woody species.

Roystonea oleracea

4. Roystonea oleracea

Roystonea oleracea (Caribbean royal palm)

R. oleracea is a palm that grows up to 40 m tall, with a distinctive, solitary, light grey, erect, cylindrical trunk. It is native to the Lesser Antilles, northern South America and Guatemala. This invasive species has been widely introduced for ornamental and landscaping purposes. It tends to be invasive in or near wetlands and can reduce diversity in areas where it becomes dominant. The dropping of large leaves and reproductive parts, which alter light intensity and humidity, have been proposed as possible reasons for these impacts. It is reported to be invasive in the swamps of the Guiana shield countries, in Panama and in the Atlantic forests of southern Brazil.

By Frank Vincentz (Own work) [GFDL ( or CC-BY-SA-3.0 (], via Wikimedia Commons

5. Urtica dioica

Urtica dioica (stinging nettle)

U. diocia is a weedy species which, as many people know from experience, has hairs which can cause an itchy sting when touched. It occurs in pastures and grasslands in monospecific clumps which can take up considerable space and thus reduce hay yields and the amount of grass available. It is normally avoided by livestock, therefore restricting their free movement. In some circumstances it can be very hard to eradicate because of its large root mass which allows it to spread vegetatively once it has established.

Other new datasheets published in November and December include:

Acacia glauca (wild dividivi)
Argemone ochroleuca (Mexican poppy)
Canine distemper virus
Centella asiatica (asiatic pennywort)
Deroceras invadens (tramp slug)
Flacourtia indica (governor’s plum)
Portulaca quadrifida (chickenweed)
Solanum capsicoides (cockroach berry)
Tephrosia candida (white tephrosia)
Xyris complanata (yellow-eyed grass)

Figure references:

  1. Cotoneaster horizontalis by peganum from Henfield, England (Cotoneaster horizontalis) [CC BY-SA 2.0 (], via Wikimedia Commons
  2. Cyperus papyrus by By Liné1 (Picture taken with my IXUS 800 IS) [GFDL ( or CC BY-SA 3.0 (], via Wikimedia Commons
  3. Persicaria wallichii by By Meneerke bloem (Own work) [GFDL ( or CC BY-SA 3.0 (], via Wikimedia Commons
  4. Roystonea oleracea by By Krzysztof Ziarnek, Kenraiz (Own work) [CC BY-SA 4.0 (], via Wikimedia Commons
  5. Urtica dioica by By Meneerke bloem (Own work) [GFDL ( or CC BY-SA 3.0 (], via Wikimedia Commons


New in October 2015 from the ISC

In October 2015 the following datasheets were published on CABI’s Invasive Species Compendium (ISC). You can explore the open-access ISC here:

Forest & Kim Starr [CC BY 3.0 (], via Wikimedia Commons

1. Mysore raspberry

Rubus niveus (Mysore raspberry)

Rubus niveus is an invasive blackberry which is threatening the endemic wildlife of the Galapagos Islands. More specifically, it is a threat to the unusual daisy tree forests (of the Scalesia genus). R. niveus now covers around 30,000 ha of the islands and can grow up to 3 m tall. CABI scientists are searching for potential biocontrol agents from the Asian native range of the blackberry to introduce here. Find about more about this project.

Christian Fischer [CC BY-SA 3.0 (], via Wikimedia Commons

2. Common knotweed

Polygonum arenastrum (common knotweed)

This species is considered to be one of the world’s most economically important weeds. It is a host of various pathogens which damage crops such as alfalfa, potato and parsnip. Phytotoxic chemicals are produced by the plant that can inhibit the establishment of black medic (Medicago lupulina) and other plant species. It can also affect rhizome bacteria which are important for legume species such as peas and beans. The weed is very resilient as it possesses a long taproot which helps it survive drought.

Forest & Kim Starr [CC BY 3.0 (], via Wikimedia Commons

3. Love-vine

Cassytha filiformis (love-vine)

Invasive in its broad native range (Asia, Africa, America, Oceania), Cassytha filiformis is a parasitic vine that is primarily found in coastal areas. In the Chagos archipelago (Indian Ocean) it is seriously reducing populations of beach cabbage (Scaevola taccada) and increasing the risk of erosion. C. filiformis extracts plant sap from its host and covers it with a dense mat of stems. The sheer weight of its stems can break branches – this is particularly problematic when its host is a crop, such as a citrus tree.


Forest & Kim Starr [CC BY 3.0 (], via Wikimedia Commons

4. Portia tree

Thespesia populnea (portia tree)

Thespesia populnea is an Old World, tropical, coastal species that is often found in and around mangroves. Its buoyant and hardy seeds can survive even after a year in seawater. It produces dark, red-brown, strong and hard ‘milo’ wood that is highly valued on Pacific islands. However, it can form dense thickets and reproduces profusely. It is listed as an invasive species in the Bahamas, Florida and Puerto Rico.

Hypogeococcus pungens (cactus mealybug)

Hypogeococcus pungens is a mealybug, native to South America, which was used as a biological control agent of invasive cacti in the subfamily Cactoideae in Queensland, Australia, and in South Africa. Since then, it has become an invasive species itself. It is a threat to native cacti in Florida and Hawaii (USA), Barbados and other Caribbean islands. In addition to cacti, its wide range of hosts includes species within the ornamental plant families Portulacaceae, Apocynaceae and Amaranthaceae.

Other new datasheets published in October include:

Baccharis pilularis (coyote brush)
Cuphea carthagenensis (Colombian waxweed)
Cyrtomium falcatum (Japanese holly fern)
Epilobium ciliatum (northern willowherb)
Maliarpha separatella (African white rice borer)

Figure references

  1. Mysore raspberry by Forest & Kim Starr [CC BY 3.0 (, via Wikimedia Commons
  2. Common knotweed by Christian Fischer [CC BY-SA 3.0 (, via Wikimedia Commons
  3. Love-vine by Forest & Kim Starr [CC BY 3.0 (, via Wikimedia Commons
  4. Portia tree by Forest & Kim Starr [CC BY 3.0 (, via Wikimedia Commons

New in September 2015 from the ISC

In September 2015 the following datasheets were published on CABI’s Invasive Species Compendium (ISC). You can explore the open-access ISC here:

Common mullein by Fritz Geller-Grimm (Own work) [CC BY-SA 3.0 (, CC BY-SA 3.0 (, GFDL ( or CC BY-SA 3.0 (], via Wikimedia Commons

1. Common mullein

Verbascum thapsus (common mullein)

A biennial herb which has naturalized in most temperate regions of the world. It grows vigorously, threatening native plants in meadows and forest gaps. Eradication is extremely difficult since each individual can produce 100,000-175,000 seeds that can remain viable for more than 100 years.

Fibropapillomatosis of sea turtles by Peter Bennett & Ursula Keuper-Bennett (Original photograph) [GFDL ( or CC BY 3.0 (], via Wikimedia Commons

2. Fibropapillomatosis

Fibropapillomatosis of sea turtles

A disease which most commonly affects the endangered green turtle. It causes internal and external tumours which can obstruct crucial functions such as swimming and feeding. First reported in the 1930s in Florida, it is now a pandemic.

Grey snake-bark maple by KENPEI (KENPEI's photo) [GFDL (, CC-BY-SA-3.0 ( or CC BY-SA 2.1 jp (], via Wikimedia Commons Mnemiopsis leidyi (sea walnut)

3. Grey snake-bark maple

Acer rufinerve (grey snake-bark maple)

With striped grey-green bark this tree is aptly named. It produces dense thickets and has been reported as an aggressive coloniser in acidic forests in Belgium. It has been introduced around the world as an ornamental plant, like so many other invasive species.

Sea walnut by No machine-readable author provided. Bastique assumed (based on copyright claims). [GFDL (, CC-BY-SA-3.0 ( or CC BY-SA 2.5-2.0-1.0 (], via Wikimedia Commons

4. Sea walnut

Mnemiopsis leidyi (sea walnut)

Being a comb jelly, this marine species has rows of ‘combs’ (groups of cilia) which it uses for swimming. It is an ‘ecosystem engineer’ which can change water transparency and water nutrient content. It has the impressive ability to regenerate from fragments larger than one-quarter of an individual.


Ficus microcarpa (Indian laurel tree)

A high-risk, aggressively invasive, strangling fig which is an agricultural weed and “garden thug” – how much worse could it be!? Reportedly invasive to some places where its specialist pollinator wasp has also been introduced. It starts life as an epiphyte, growing on a tree’s surface, before sending its aerial roots down to the ground. The roots end up forming a lattice around the trunk of the host tree which remains after the host tree dies.

Figure references

  1. Common mullein by Fritz Geller-Grimm (Own work) [CC BY-SA 3.0 (, CC BY-SA 3.0 (, GFDL ( or CC BY-SA 3.0 (, via Wikimedia Commons
  2. Fibropapillomatosis of green turtle by Peter Bennett & Ursula Keuper-Bennett (Original photograph) [GFDL ( or CC BY 3.0 (, via Wikimedia Commons
  3. Grey snake-bark maple by KENPEI (KENPEI’s photo) [GFDL (, CC-BY-SA-3.0 ( or CC BY-SA 2.1 jp (, via Wikimedia Commons
  4. Sea walnut by ‘No machine-readable author provided’. Bastique assumed (based on copyright claims). [GFDL (, CC-BY-SA-3.0 ( or CC BY-SA 2.5-2.0-1.0 (, via Wikimedia Commons

New in August 2015 from the ISC

In August 2015 the following datasheets were published on CABI’s Invasive Species Compendium (ISC). You can explore the open-access ISC here:


Bidens frondosa (beggarticks) – native to North America, this herbaceous annual has a range of medicinal, herbal and decorative uses and been introduced throughout Europe as well as New Zealand and parts of Asia. The seeds can easily attach to fur and clothes, helping spread the plant to new areas.

Opuntia elatior (red-flower prickly pear) – the prickly pears are proving a prickly problem, with many Opuntia species invasive outside of their native range. O. elatior is less widespread than some, but has still been introduced to India, Southeast Asia, South Africa and Queensland. Biological control has had some success with this species.

Stictococcus vayssierei (cassava root mealybug) – found in Equatorial Africa, S. vayssieri feeds on the root system of the cassava plant, causing leaf-fall, wilting, tip dieback and occasionally death. Although it has only been reported in Cameroon and the Democratic Republic of Congo, the cassava root mealybug can cause yield losses of up to 100% and could pose a major threat to cassava production in Central Africa.