Peter Neuenschwander: How Africa can control invasive pests

P Neuenschwander
P Neuenschwander
The “father of biocontrol”, Peter Neuenschwander, joined IITA’s biocontrol project against the cassava mealybug in 1983. The project was later expanded to include biological control and integrated pest management of mango mealybug, spiraling whitefly, and floating water weeds. He retired in 2003. Last year, the International Organization for Biological Control recognized his life-long contributions to biological control by giving him Honorary Membership. In this interview with Godwin Atser, he bares his mind on the contribution of biocontrol and strategies on how Africa can check invasive pests.

Please explain the concept of biocontrol.
Biological control is a technique whereby we use natural enemies to combat pests. The pests can be insects, mites, pathogens, or even plants. Most times we apply biocontrol against invading pests. The beauty is that once something works, it spreads on its own and it carries on its business without difficulties.

Please give an overview of your work on biocontrol in Africa.
The cassava mealybug was actually one of the things that brought me to Africa. The mealybug was introduced in Africa in the 1970s. Eventually parasitoids were found in South America and transported here. With national partners, we made about 150 releases in most sub-Saharan African countries. From there we went on to other projects such as the mango mealybug, and water hyacinth control.

How can biocontrol check the spread of invasive pests in Africa?
Biocontrol is good; it slows the pests but it would have been best not to have introduced those exotic organisms in the first place. So, we need to strengthen and train the quarantine people.

We also need to tighten quarantine services in all African countries, not just on land borders but also the seaports and the airports so such invasions which cost so much can be reduced.

What has been the impact of biocontrol?
For the cassava mealybug alone, the project resulted in money directly going to the farmers with the entire cassava improvement project in Africa.

What are the challenges you faced in the biocontrol projects?
Our main challenge is the uptake or adoption by the countries. Countries are autonomous in their decisions to import or not to import.

So, we have to convince some 30 quarantine authorities that they should give us quarantine permits, that they should help us, and that they should allow the insect to come in, and so on.

The challenges also include unsatisfied expectations from colleagues from different disciplines who expect us to extinguish the pest. We don’t really extinguish anything.

What is the perception of people towards biocontrol?
The public in most cases is more afraid of biocontrol (insects) than the invasion itself. This is because they don’t understand how it works.

Does biocontrol break down?
In technical terms, yes, it can break down—when biocontrol is working and you forget about it and suddenly start spraying the field with pesticides. That is, you kill the natural enemies and the pest.

What is the future of biocontrol?
The demand for biocontrol is already there and there will always be invasive pests. We also have to maintain the human capital in biocontrol. Unfortunately, the capacity in biocontrol worldwide is declining, not only in IITA.

Your colleague referred to you as the father of biocontrol. Can you comment on this.
I am the last surviving biocontrol specialist at IITA. That was what was written about me when I retired 6 years ago. I am still helping out.

What were the most exciting moments in your work on biocontrol?
The excitement was going out in the field and also the fact that I had a “privileged” job. It also includes getting recognition. In the scientific world, the cassava mealybug project was seen as a success.

You have been retired for several years now. What’s next?
I have a request to go to Asia, because after 20–30 years, the cassava mealy bug turned up in Asia, and it is spreading. They want us to introduce biocontrol to curtail the spread.

Rachid Hanna: Balance strategic research with development initiatives

Hanna inspects banana plant
Hanna inspects banana

Rachid Hanna is an entomologist by training with a diverse academic background (BSc in Horticulture, MSc in Plant Protection and Pest Management, PhD in Entomology). He joined IITA-Bénin in 1998 to lead the cassava green mite (CGM) biological control program. In Bénin, he initiated several other programs on biocontrol and IPM of other crop pests. He recently relocated to IITA-Cameroon and has been entrusted in helping to rebuild the research program with a new focus.

What were the differences in research priorities when you first started working for IITA and now?
When I joined IITA, there were several ongoing or recently concluded and highly successful biocontrol programs. We now need to give more attention to developing biological control options for insect vectors of the causal agents of serious crop diseases. There is still considerable appreciation within IITA and among our partners for the potential for biological control to solve many pest problems in agriculture, with numerous invasive pests lurking outside African borders. We need to maintain the capacity to provide a rapid response to these alien species. Biological control is often the only viable and sustainable solution.

IITA went through a period when scientists were pulled more toward the development side as core funding declined. It seems we now have a good balance in the R4D continuum. At present there is increased emphasis on biotechnology—molecular biology in particular—but natural resources management has suffered. IITA has also put greater emphasis on the commercialization of agricultural products as a means of reducing farmers’ risks and increasing farm income. It has also given increasing attention to food safety and human health.

What are your current projects?
We have spent a lot of time and resources figuring out how CGM biocontrol works through predators and acaropathogens, and determining its socioeconomic impact. I have also been involved in classical biological control of the coconut mite, which is present in the Americas, Africa, and the Indian subcontinent.

IITA and icipe have been collaborating for the last 3 years on a BMZ-funded project to develop IPM for several mango pests. At the core of this project is biological control of the invasive fruit fly, Bactrocera invadens, or Sri Lanka fly that is now present in at least 34 countries in Africa where it has caused huge losses in fruit production. With icipe we have explored natural enemies of this pest in Sri Lanka, its putative origin, and imported from Hawaii, tested, and initiated field releases of Fopius arisanus, a parasitoid known to be an excellent biocontrol agent of several fruit fly species closely related to the Sri Lanka fly. We have already released nearly 95,000 individuals of F. arisanus in Bénin and Togo, with encouraging recovery rates.

More recently, I began research on the banana aphid, also an exotic pest in SSA, and the only known vector of banana bunchy top virus that causes a very serious disease of banana and plantain. This disease is presently found in 12 countries in Africa and continues to move to others. IITA, in collaboration with partners, has initiated efforts to develop integrated options to control the banana aphid with emphasis on biological control.

For some years, I have been developing with several partners IPM for the African root and tuber scale, a pest of cassava in Central Africa. This pest is indigenous to Central Africa where it has evolved on native hosts in association with an indigenous ant on which it depends for its survival and dispersal. We figured out how to deal with the scale using ‘less scale-suitable’ varieties, cultural practices that reduce the frequency of hosts that serve as a reservoir for the scale, and ecofriendly baits to kill the ants. To complicate matters even further, we recently discovered—using molecular biology tools—that the scale is a complex of species and not one species as has been suggested based on morphology. This work is part of a larger IFAD-supported project to develop integrated management approaches to high-profile cassava pests and diseases in SSA. Swiss funding is supporting a PhD student to elucidate the ecological factors that promote ant abundance and the nature of ant/scale interactions.

What is unique about biocontrol research?
We seek to develop sustainable solutions to major pest problems that limit agricultural productivity. Nearly all this research has unique scientific aspects. Biological control is not really new. It is a useful approach, but the process of discovery of natural enemies, understanding how they work, and promoting their abundance and persistence has many innovative and unique aspects.

What are your challenges at work? What are the rewards?
There are many challenges. One is farmers’ acceptance of the technologies. Farmers like simple solutions to their problems. With biological control, the natural enemies work on their own, mostly without the farmers’ intervention. In contrast, the success of a crop-variety pest control approach will largely depend on the farmers’ acceptance of the varieties.

The breadth of our geographic coverage is also challenging and at times daunting. There is considerable restriction now on the exchange of biological materials and it is becoming increasingly difficult to export, import, and test natural enemies.

The rewards are equally many. Chief among these is the satisfaction of getting farmers to adopt a new practice and so achieving a noticeable impact in our work. The satisfaction of discovering a new natural enemy and figuring out how it goes about its business of consuming and suppressing its prey is immense.

Discovering and describing a new species is equally satisfying. So are seeing students successfully complete their training and becoming full-fledged members of the scientific community, and farmers’ glowing and wide eyes when they see through a hand-held magnifying lens the little mites that cause the damage to their crop, or the equally small predator that kills those pests and protects their crop.

We also get rewards through the recognition we receive from our employer and peers.

What is the impact of your work on African farmers, producers, and consumers?
The return on investment from biocontrol can be very high and the results are permanent. Except on rare occasions, farmers need not intervene at all.

All the work we are doing on biological control is important for agriculture. Take for example the work on cassava mealybug and CGM biocontrol. These pests devastated cassava production across the cassava belt in SSA. Their control has resulted in preventing billions of dollars worth of losses to African agriculture and translates to more food security and income. The cassava mealybug has already invaded Thailand, and its farmers stand to reap the benefits from our work. The same is true for the other pests for which we trying to develop sustainable solutions. This underscores the fact that biocontrol benefits can be obtained independent of the location where it was developed.

We are now trying to do the same with disseminating control measures for the African root and tuber scale in the Congo basin, coconut mite in Bénin, Tanzania, and Sri Lanka, the highly destructive Sri Lanka fly, and the banana aphid. Each of these achievements will have considerable positive impact on the productivity of targeted crops, in turn enhancing food security and people’s livelihoods.

Who are your collaborators?
We have an excellent network of collaborators both in Africa and abroad, and a cadre of superb students and support staff. My main collaborators on strategic research have been IITA scientists and those from universities and government institutions in Europe, United States, Brazil, and Kenya. In Africa, I have worked closely with icipe and more than 14 NARS—government and university—partners in adaptive research and technology transfer. While not all collaborations were equally successful, the best were those when all partners had ownership, trusted one another, had common interests, and were fully engaged.

Any insights for colleagues or partners?
Keep an open mind. Strive to be a scientist in search of new knowledge that can be translated to ways of improving people’s livelihoods. For crop protection specialists, give biological control a chance. It is permanent, the safest, and most ecologically—and in most cases most economically—sound means of pest control.

Start thinking of the next project (or phase) or research topic as soon as you start one. Think big and act with humility.

Hanna interacts with farmers and extension agents
Hanna interacts with farmers and extension agents

To our partners: IITA is with you. Let’s keep working together for we can achieve a great deal more together than alone.

How could IITA be more effective?
IITA is a very effective R4D organization; this is largely due to an appropriate balance between strategic research and development activities at present. However, we may be presently too spread out. Expansion often happens at the expense of existing posts. Some posts that have been very effective in R4D should be strengthened. Plant health and crop improvement research have led to huge impact; let’s continue to give them priority and support.

Biodiversity should be everyone’s business. We are well placed to work on biodiversity and conservation while enhancing crop productivity and livelihoods. We need to recruit topnotch scientists and keep them. We should promote a healthy work environment. We should also reestablish and restore the student training program to its previous prominence; the large majority of our NARS collaborators were trained through this program. Many are now older or retired. IITA has recently increased investment in specialized training of its entire staff. This is a good move.

Ranajit Bandyopadhyay: Ending aflatoxin contamination in Africa

Developing countries lose billions of dollars in trade annually to aflatoxin contamination in foods. Worst still, the contamination endangers the health of millions of people in the region. But the good news is that IITA has developed a biocontrol product (aflasafe) to tackle this problem. Ranajit Bandyophadhay speaks to Godwin Atser on the journey that led to the development of aflasafe and other issues.

Ranajit (left) explains to partners how aflasafe works
Ranajit (left) explains to partners how aflasafe works

Tell us about your work at IITA
I am a plant pathologist, and one of my main responsibilities is how to manage plant disease. The other is to ensure food safety.

What about your work on biocontrol?
This is one the most exciting projects that I have ever had. The work on biocontrol is on a toxin found on maize and peanuts called aflatoxins. The toxin causes a lot of harm to people’s health and also makes farmers sell their products at lower prices. So, the losses are both in terms of health and trade. What I am trying to do is to manage the aflatoxins using a holistic approach, such as using resistant varieties, better crop management practices, and also the biological control method.

What is unique about your biocontrol work?
One thing that is unique is that we are using the natural resources from Nigeria to manage an economic and medical problem. We are making use of nontoxic fungi to eliminate the harmful fungi (aflatoxins).

Why are aflatoxins important?
Aflatoxins are harmful chemicals that are produced by a fungus called Aspergillus flavus.

The fungi produce toxins in maize, peanuts, and generally grains. When people eat them, it harms them and causes diseases such as liver cancer and kwashiorkor, among others. Worst still, farmers cannot sell their products at the premium price.

What makes you keen about biocontrol?
It is one of the strongest components of the holistic approach. If we can have the biocontrol approach adopted by farmers, most of the problems concerning aflatoxins which they face during postharvest will be greatly reduced.

Do you see IITA in the position to offer the biocontrol option to farmers?
Absolutely yes. The reason is that we actually started with good science and that science has given birth to a new product which the farmers are willing to use.

Happy farmer with aflasafe
Happy farmer with aflasafe

Tell us about this product
The product is “aflasafe”. We coined the name aflasafe; when farmers use the product on their farms, they would produce grains that are free from aflatoxins.

Did you face any challenge in developing the product?
The first challenge was developing the product itself. The fresh challenge now is how to get a large manufacturing firm to begin massive production, advocacy, and awareness so that it gets to the farmers.

Any interest so far?
We made a presentation to the Minister of Health, Prof. Babatunde Osotimehin, and he was so excited about the product. We also did a field deployment and the farmers were also very happy about it.

Who were your partners in this work?
Many organizations and people were involved in this work. They include the AATF, National Agency for Food and Drug Administration and Control, farmers, United States Department of Agriculture, US Agency for International Development, Prof Peter Cotty, Dr Joseph Atehnkeng, and several others.

How were you able to handle these partners?
Every partner is a unique entity but one thing important is to build trust. Once that is done, the partnership gets smooth.

Research wise, what are you future plans?
My future plan is to get this product used on at least one million hectares. I intend to put all my efforts to see that this product is used for the benefit of the farmers in general and women and children who are more vulnerable to aflatoxins.

Related website

Aflatoxin management website – www.aflasafe.com

Manuele Tamò: Biocontrol should be the first option

Manuele Tamo inspects plant
Manuele Tamo inspects plant. Photo by IITA

Dr Manuele Tamò is the Officer-in-Charge of IITA-Bénin. In this interview, he talks about the outlook regarding invasive pests in Africa and the role of biocontrol.

Africa seems to be witnessing a lot of invasive pests. What are the factors responsible for this?
That observation may be a bit of an exaggeration at the moment. However, we have been experiencing some invasive species in the past years and, unfortunately, that might increase in the future. This is mainly due to the increase in people’s travels—people travel but do not know that they are carrying pests in their suitcases. Trade is also another contributing factor to the spread of invasive pest species in Africa.

What control measures have governments put in place to check this trend?
We have Plant Quarantine officers all over Africa. They are doing their best but, unfortunately, in West Africa, for instance, the borders are porous so people can pass through from one country to the other without much control. Also some of the invasive species spread freely and once they land on the continent the quarantine officers have no control over them.

How does biocontrol help in this instance?
Biocontrol is a natural response to controlling invasive pest species. It simply means reuniting the invasive species and its natural enemies found it its area of origin. This is what is called classical biological control.

How has your work on biocontrol helped in the control of, for instance, cowpea pests?
Let me start with the project on flower thrips (Megalurothrips sjostedti) that may be the oldest one—we have found a new natural enemy and we are spreading it all over West Africa. We are monitoring the situation in Bénin, Ghana, and also in Nigeria where we made the releases.

For the cowpea pod borer (Maruca vitrata), we have just introduced a new natural enemy from Asia. Our aim is to release it and establish it on wild occurring host plants so that the M. vitrata population that is able to invade cowpea farms will be much reduced.

What is the damage caused by these pests on cowpea?
The damage can be devastating. If you take a susceptible variety in an uncontrolled situation, you might get about 80% yield loss, at least.

Some people worry that results from biocontrol never come early. What is your reaction to this statement?
Biocontrol is both a science and an art. As scientists, we know that experiments can take several years before results are achievable and thus conclusions are made. Just as it takes several years to develop a new crop variety, so it is for biocontrol.

The cassava mealybug biocontrol project gave results already after 2 to 3 years. This has raised stakeholders’ expectations. Now, every time we embark on a biocontrol project, farmers and also politicians expect us to have the same level of success within 2 to 3 years.

In certain cases, results are obtained quite rapidly, but at other times, it might take 5 to 10 years. Results vary because we work on various types of insects that live in different environments.

On the other hand, biocontrol is an art because sometimes you need luck to get quick results.

Why biocontrol and not pesticides?
I am not against pesticides if they are used correctly to save crops from pest attacks. But biocontrol is an option that controls pests by reestablishing the natural balance (in nature) and should be considered first, particularly in the case of alien invasive species.

What are your future plans?
Continue the work on flower thrips and Maruca vitrata and measure the impact. I am also working on a feasibility study on cotton. Cotton is the biggest consumer of insecticides in the whole of West Africa, and a source of concern with regard to environmental and human health.

We also want to start a new project investigating insects attacking cashew. The project is important because cashew nuts exported to Europe and the United States must be pesticide free.

How do you work with the government in achieving your results?
We collaborate with the government, starting with the Plant Protection Services. For instance, we need to comply with country quarantine regulations for the introduction of new biocontrol agents. Plant protection officers are with us in the field—from experimental releases of natural enemies to measuring establishment and impact. We also work with the NARS, which include research institutes and universities, by offering training to students and collaborators.

Biological Control 101

Chemical pesticides have become a mainstay in pest management because of their “quick-fix” effects and their ease and convenience of use. Their use over time, however, has some negative effects on human health and the environment.

Farmer in Parakou, Benin, participates in the release of Fopius arisanus, a parasitoid of Bactrocera invadens
Farmer in Parakou, Benin, participates in the release of Fopius arisanus, a parasitoid of Bactrocera invadens

Biological control or biocontrol is an alternative to the use of chemical pesticides. It uses natural “enemies” to reduce pest populations and their damage to crops and food products. These enemies include predators, parasitoids, or pathogens.

Biocontrol approaches build on the natural control already existing within an ecosystem by strengthening a naturally occurring enemy or by importing and introducing a natural enemy into that ecosystem.

Predator and pest mites
Predator and pest mites

IPM toolbox
Biocontrol is just one of the many components in the integrated pest management (IPM) toolbox that includes, among others, the use of cultural practices, planting of resistant or tolerant crop varieties, and the application of inorganic (or chemical) pesticides.

Biological alternatives involve the use of biological control, biological pesticides, botanicals, semiochemicals, and transgenic organisms.

Biocontrol
Biocontrol is the use of natural enemies, also called biological control agents, such as predators or parasitoids that attack the pest to reduce pest damage. In an undisturbed ecosystem, insects, mites, or microorganisms, and other species that prey on or parasitize different species are part of the natural control or balancing mechanisms.

Biocontrol approaches include conservation biocontrol, augmentation biocontrol, and classical biocontrol.

10Maize cob being co-inoculated with toxigenic and atoxigenic strains to identify competitive atoxigenic strains in the field
10Maize cob being co-inoculated with toxigenic and atoxigenic strains to identify competitive atoxigenic strains in the field

Conservation biocontrol enhances the effectiveness of natural enemies already present in the ecosystem through, for example, the application of cultural practices. Examples include planting food sources for natural enemy pests or reducing the amount of chemicals in the system to allow natural enemy numbers to increase.

Augmentation biocontrol means the addition of a predator or parasitoid to an ecosystem to increase numbers or begin a new population when the natural enemy has disappeared. Inoculation is adding small numbers of the species, which increase naturally over time, whereas inundation means adding large numbers of the natural enemy for a rapid effect on the pests.

Classical biological control involves importing natural enemies to a location where they have not been present before, especially, when a pest has been accidentally introduced. Classical biocontrol has been applied successfully to control hundreds of pests in horticultural and field crops and in forestry. Despite the initial high investment, it is the most economical form of pest control.

Biopesticides

Diseased cassava leaf
Diseased cassava leaf

Biopesticides involve the use of pathogens—microorganisms that cause disease—to kill pests. Also called microbial pesticides, they contain pathogenic microorganisms as their active ingredient, e.g., bacterium, virus, fungus, nematode, or protozoa. They are applied in a manner similar to chemical pesticides, but their “live” ingredient gives them a potentially greater advantage over chemicals since this is able to reproduce and provide continuing pest control.

Some popular examples include the use of Bacillus thuringiensis (Bt), which naturally occurs in the soil and in plants, or mycopesticides (insect-killing fungi) such as Beauveria bassiana and Metarhizium anisopliae, which attack a relatively wide range of insects. IITA has been using these fungi for its biocontrol work.

Botanicals

<em/>Bactrocera invadens ovipositing on a mango fruit” title=”11Bactrocera invadens” width=”250″ height=”188″ class=”size-full wp-image-1149″ /><figcaption class=Bactrocera invadens ovipositing on a mango fruit

Also called botanical pesticides, these contain plant extracts that have biocidal properties. The best example is the use of the extracts from the popular neem tree (Azadiracta indica) (active ingredient: azadirachtin), which can be used to disrupt molting in a wide range of insect pests. Such botanicals can be grown alongside agricultural crops.

Semiochemicals
These are chemicals produced by insects and other species that stimulate behavior or interactions, and are used to manipulate behavior to control pests. Well-known examples are pheromones, which stimulate behavior between individuals of the same species, and allelochemicals, which mediate interaction between different species.

Transgenic crops
Transgenics contain protectants produced by the plants themselves, following the introduction of genetic material coding for that substance, as in Bt transgenic plants, e.g., Bt maize, potato, and cotton. The gene coding for the Bt toxin is inserted into the chromosome of the crop plant so that the plants themselves become toxic to the pest.

Source: SP-IPM. 2006. Biological alternatives to harmful chemical pesticides. IPM Research Brief no. 4. SP-IPM Secretariat, IITA.

Biological control at IITA: past, present, and future

Rachid Hanna, r.hanna@cgiar.org

Banana bunchy top and banana aphid survey, DR Congo
Banana bunchy top and banana aphid survey, DR Congo. Photo by IITA

Biological control is one of the oldest and most useful and ecofriendly approaches to pest management.

IITA has had an excellent tradition in biological control which has given it some of its greatest successes. These were captured by Peter Neuenschwander in his 2004 commentary in Nature.

The past and the present
The invasion of Africa by the cassava mealybug and the initial failure to find a solution to this devastating pest marked the start of a series of highly successful biological control efforts led by IITA in collaboration with partners from Africa and from around the globe. The mealybug invasion was shortly followed by the cassava green mite, also originating from South America. The duo devastated production throughout the cassava belt. Finding a natural enemy—a tiny parasitic insect (renamed several times) Anagyrus (=Apoanagyrus =Epidinocarsis) lopezi—for the control of the mealybug was relatively quick. Once it was released, the parasitoid quickly established. Aided by over 150 additional releases and within a span of 12 years the parasitoid covered nearly all of SSA, in the process leading up to 90% reduction in cassava losses and up to US$29 billion in estimated value of crop recovery.

The campaign for green mite biological control followed an approach similar to that of the mealybug, but it took much longer to find appropriate predators that would eventually provide the control needed for cassava recovery from the two South American invaders. Three promising predators (tiny phytoseiid mites) were established, one became extinct, another was restricted to humid regions, and a third species (Typhlodromalus aripo) became nearly the equivalent of A. lopezi (without the many name changes!).

Within a span of 11 years and over 450 additional releases, T. aripo has been established in at least 22 countries. Where it has been present for 2 or more years (and where cassava varieties have at least partly hairy apices that are favorable for T. aripo colonization and persistence), it brought down losses to the mite from an average of 35% to below 10% (after mealybug control), resulting also in billions of dollars in crop recovery.

The mealybug and green mite campaigns have been credited for bringing the capacity of biological control to SSA and spreading its science and practice as no other on any continent has done. Several successful projects followed, including that of the mango mealybug (an invader from India) and the spiraling whitefly (a polyphagous pest from the Caribbean), and extended to control of the water weeds. These successful efforts added another billion US$ in estimated savings.

Typical damage by pod borer caterpillar. Photo by IITA
Typical damage by pod borer caterpillar. Photo by IITA

These campaigns provided the stimulus and the capacity to build on successes with the continuation of biological control efforts at IITA. Presently, cowpea thrips and cowpea pod borer are being fought with the tiniest of known parasitoids (for thrips) and with a combination of a parasitic wasp and a virus (for cowpea pod borer). Programs are under way to tackle several other devastating pests: the coconut mite (from South America), the banana aphid (an invader from Southeast Asia and the only vector of the devastating banana bunchy top virus), the Sri Lanka fruit fly (now present in 24 countries and on more than 50 host fruits in Africa), and a variety of indigenous pests including the African root and tuber scale (in the Congo Basin), the sweet potato whitefly (vector of cassava mosaic viruses throughout Africa), cotton worms, several pests of cashew, and several fruit fly pests of fruits and vegetables.

However, biological control of indigenous pests is much more challenging than the control of exotic pests and tends to be insufficient alone. It often requires integration with one or more approaches, such as host plant resistance and cultural controls, among others. A prime example of this challenge is the control of the whitefly Bemisia tabaci, the vector of the viruses that cause the devastating cassava mosaic and cassava brown streak virus diseases in cassava fields in Africa (J. Legg, this issue). B. tabaci can be controlled with inundative releases of parasitoids and predators in protected and high-value agricultural systems. However, biological control alone has not been sufficient. Other complementary tactics, particularly host plant resistance, are necessary if we are to rein in this pest.

<em srcset=Bactrocera invadens ovipositing on a mango fruit” width=”250″ height=”188″ />
Bactrocera invadens ovipositing on a mango fruit. Photo by IITA

IITA in partnership with the Centre de cooperation internationale en recherche agronomique pour le developpement and Africa Rice has recently demonstrated the usefulness of the weaver ant in fighting off pests of mango and other tree crop pests. A sister species has been used in pest control by the Chinese for thousands of years. The article by Vayssieres et al. (this issue) shows that this native predator works principally by repelling the damaging fruit flies. The effectiveness of this ally has been demonstrated. Now its full potential is being exploited through a campaign to inform farmers how to manage this ant to promote its abundance and provide an additional weapon in the sustainable control of fruit fly pests.

Nearly parallel to the development of biological control with parasites and predators in Africa is IITA and its partners’ pioneering work on the development of microbial agents for the control of a variety of pests and pathogens.

The first pioneering success was the development of the biopesticide Green Muscle®. Based on a naturally occurring fungus Metarhizium anisopliae var. acridum, this natural and now commercial product has proved to be the weapon of choice against a variety of devastating pests, such as the red and desert locusts.

The successes of biocontrol of the mealybug with parasitoids and green mite with predators opened the gate for numerous other programs that relied on arthropod biocontrol agents. The success of Green Muscle® has also given substantial impetus to a variety of other efforts aimed at harnessing the power of naturally occurring microbes to fight harmful pests.

Microbial agents are being developed for pests that are very difficult to control, such as parasitic weeds. IITA’s efforts to rein in the parasitic weed Striga hermonthica or witchweed is paying dividends. Striga attacks maize, sorghum, and millet, often the sole staple crops in many areas of the Sahel of West Africa. Biocontrol agents—host-specific strains of the common pathogen Fusarium oxysporum f. sp. striga—in combination with Striga-resistant/tolerant varieties are giving farmers in SSA hope for controlling a scourge that causes some $7 billion in annual crop losses.

Similarly, IITA and its partners have found strains of the fungus Beauveria bassiana that can serve as a full replacement to toxic pesticides used to control the diamondback moth, a pest that can cause complete loss of cabbage crops if unchecked. This pest has developed resistance to many pesticides and has forced farmers to rely on the excessive application of pesticides that are not even meant for use on food crops, such as cabbage. That treadmill can end with the new microbial agent.

Aflatoxin-contaminated groundnut kernels in Mozambique
Aflatoxin-contaminated groundnut kernels in Mozambique. Photo by IITA

More recently microbial control has taken another innovative and pioneering direction at several IITA locations in SSA. In a twist on the concept of using beneficial arthropods to fight off harmful arthropods, fungi that do not produce mycotoxins were identified and used to exclude toxogenic strains that contaminate stored grains. Similarly, endophytic fungi that grow harmlessly inside the banana plants have been used to impart resistance to pests such as weevils and nematodes that have, in some places, resulted in farmers abandoning banana and plantain production.

The list goes on. Last but not least, entomopathogenic nematodes are being explored for the control of an indigenous pest—the African root and tuber scale—and an exotic pest—the banana weevil.

For as long as there are problems and experienced scientists and staff to deal with emerging problems, IITA will continue to strive to be a leader in the field of biological pest control.

Key to successes
At the heart of these efforts and as the key to this success were fruitful partnerships and sustained donor support. The message: complementary capacity—be it geographic, scientific, or political—is essential for the development and implementation of successful technologies on a continental scale. (IITA’s partners and donors can be found on our Web site at www.iita.org). IITA’s partners are from all corners of the globe and run the spectrum of all research and development institutions. The core are CGIAR sister centers, universities, government (including NARS) and UN agencies, and (more recently) the private sector.

The sustainability of biological control has numerous requirements. Chief among them is donor and institutional commitment followed by the recruitment and retention of highly experienced scientists to lead the development of innovative pest control. All require long-term commitment, because the goal can take a long time to achieve but the payoff is often handsome.

While the mealybug and green mite programs brought biological control to Africa, training of African scientists has been the key to the successful dissemination of the capacity to do biological control. IITA has led this effort in Africa. The continuity and scope of such training will be necessary if we are to emulate past successes.

Of particular significance and another central element in the success has been the correct identification of pests and natural enemies; this is fundamental because it provides knowledge not only on identity but also about origin and distribution, biology, association with other organisms, evolutionary relationships, and other important topics. Without the proper naming and organization of organisms, biological control would be haphazard and chaotic, and can lead to failure and considerable waste in time and resources.

Scientist explains to farmer how aflasafe works on maize. Photo by IITA
Scientist explains to farmer how a biopesticide works on maize. Photo by IITA

Lessons
The scientific lessons learned from past and present efforts are numerous.

Anagyrus lopezi, the parasitoid responsible for the control of the cassava mealybug, is host specific and has an incredible capacity for dispersal (about 350 km per year) and for finding its host, which had been key to its ability to keep mealybug populations at low levels. The parasitoid originated from the LaPlata Valley (Paraguay) where conditions are not like those common in Africa. Nevertheless, A. lopezi proved to be highly adaptable. It quickly established and efficiently controlled the mealybug from the Sahel to the Congo Basin and to the East African Highlands. This example highlights some difficulties in predicting the outcome of biological control introductions that otherwise would eventually prove effective in controlling the target pests while relying on classical criteria for selecting natural enemy candidates.

A similar lesson was drawn from the green mite biocontrol program. Eleven species of predatory mites were introduced into Africa during the exploration phase of the program. T. aripo was the least efficient in terms of predation and efficiency in turning energy from consumed prey into the production of its own offspring. However, it turned out to be best at becoming established and dispersing (> 200 km per year), and in controlling green mite. The key was not its voracity but its ability to use the apical growing point of cassava as a shelter, to be so tuned to cues from its plant and prey to locate them, to use plant-based food for sustenance during periods of low prey abundance, and to have a phenomenal dispersal capacity. This is a landmark lesson: voracity and rate of population growth need not be always the top criteria in selecting effective natural enemies, as by these criteria, T. aripo would not have been selected for introduction into Africa.

The future
Invasive weeds and arthropods continue to hamper development and ravage and disrupt agricultural and natural ecosystems, and doubtless many will continue to make it through porous borders. IITA has been a leader in developing options for controlling the invaders and restoring that balance. While classical biological control will likely continue to be the preferred way to deal with invaders, greater intensification of agricultural production, with its associated reliance on external inputs, necessitates an integrated approach. Biological control will be a component of a package that may include selective pesticides, varietal resistance, attractants and behavioral disruptants, as well as appropriate agronomic practices.

Hans Herren—former IITA scientist and recipient of the World Food Prize—in his foreword to the book on Biological control in IPM Systems in Africa (Neuenschwander et al. 2003, editors) wrote: “Biological control, however, cannot be a substitute for mismanaged plant production, in short, for bad farming. To have access to the full power and potential of biological control, the crop production system needs to be fully integrated in the larger agroecosystem, fulfilling the principles of agroecology. Under such a system, the powers of biological control can best be unleashed, and its synergistic effects with host plant tolerance/resistance, habitat management, and agronomic practices brought to bear maximum impact.”

Farmers field school on IPM in Mali
Farmers field school on IPM in Mali. Photo by IITA

The old and timeless adage—an ounce of prevention is worth a pound of cure—captures the essence of the need and value of preventing the invasion of new species. Key to effective prevention is the development and maintenance of the capacity for quarantine, surveillance and readiness to develop appropriate options to deal with the invaders and limit their impact on African agriculture and the rest of the African ecosystems.

We also need more modeling for predicting the distribution and abundance of pests and their potential natural enemies to guide the development of experimental approaches to pest problems. Climate change can affect pests and their natural enemies in many ways. Modeling, along with long-term monitoring and demographic studies can be useful approaches to determining the effects of climate change on pests and their natural enemies.

Greater emphasis is needed on the use of the modern tools of molecular biology to trace the origin of invaders and use that knowledge to search for natural enemies where the invaders originated. Taxonomic services (and their associated collections) have been and will continue to be one of the essential tools in successful programs. In addition—and among their many uses—biodiversity collections can often serve as the first stop for foreign exploration against pests and weeds on other continents.

The targets will doubtless change. Highly trained and experienced staff will always be necessary to address the new targets. We also need to continue to strengthen existing links and develop new complementary partnerships. Training of local staff and African scientists is essential for them to become leaders in biological control in their countries, capable of running their own programs.

The younger generation is the one to find the solutions to future threats to the continent’s food security and livelihoods of its inhabitants. Improvements in the health of ecosystems will go a long way in protecting and promoting biodiversity. Biological control, if carefully developed and implemented, is the greenest approach to saving farmlands, waterways, savannas, and forests from the ravages of pests.