Impact Assessement of biological control in Africa –20 years experience of
the International Institute of Tropical Agriculture
Peter Neuenschwandera , Hugo De Grootea,* , Boru Douthwaiteb
a
International Institute for Tropical Agriculture (IITA), 08 B.P. 0932, Cotonou, Benin
IITA, Ibadan, Nigeria
b
*
corresponding author, present address: H. De Groote, CIMMYT, POBox 25171 Nairobi,
Kenya, h.degroote@cgiar.org
Abstract
This paper presents the experience of the International Institute of Tropical
Agriculture (IITA) with impact assessment of biological control in Africa. The history of four
case studies are presented: cassava mealybug, cassava green mite, mango mealybug and
water hyacinth. To counter these alien pests, natural enemies was identified in the region of
origin, studied in quarantaine, raised and released. All impact studies show high returns to
investment, with benefit cost ratios ranging from 149 to 420, indicating high suitability of
biological control for the African environment. Though the documented biological control
projects present very sustainable solutions and are clearly highly profitable, its profile with
donor agencies is rather low. Some of the reasons presented here are the lack of guarantee for
a sustainable solution from the outset, the long time frame required, the limited potential for
collaboration with the private sector, and the lack of visibility and related public awareness.
For these reasons, biological control and IPM are often not given their share of recognition
within the CGIAR system and the donor community. It is therefore recommended that
biological control and IPM projects include an impact assessment component from the
beginning, to help guide the development of the technology and document the potential
impact from the start. Further, more effort is needed to bring the impact of biological control
to the attention of the general public and the donor community.
Keywords: Economics of biological control, benefit-cost analysis, impact assessment, pest
management, Africa
1. Introduction
The International Institute of Tropical Agriculture (IITA) has a long experience with
biological control in Africa (Neuenschwander, 1996), consisting of bringing in natural
enemies of alien pests. Since the widely publicized success of the Africa-wide biological
control of the cassava mealybug (Neuenschwander, 1994), successful classical biological
control projects have been undertaken with the partners of the National Agricultural Research
Systems (NARS) against the mango mealybug, the cassava green mite, and water hyacinth.
Initially, all projects documented the impact of the introduced exotic natural enemy on the
invading pest species and the food-web consisting of indigenous species. This was followed
2
up by studying the impact on crop production, and by quantifying the amount of avoided crop
loss due to the biological control intervention, and translated into economic gains for farmers
and/or consumers. It took more than 10 years after the start of the cassava mealybug project
for the first impact study to be published (Noorgaard, 1988). The nex study, still on cassava
mealybug, took again more than 10 years (Zeddies et al. 2001). Only recently, further studies
have been finished on mango mealybug (Bokonon-Ganta et al, forthcoming ), water hyacinth
(De Groote et al. 2002), and cassava mealybug (Coulibaly et al., 2002) and are at different
stages of being published.
The question arises if these projects and their impact assessment were able to
influence priority setting within the collaborating institutes (IARCS and NARS) and the
policy and decision making within the donor community? This paper presents the history of
four classical biocontrol projects and an overview of the ex post economic analyses of the
different projects, a synthesis of the ecological impacts and a first attempt to quantify the
impact on the national programs. Then, it analyses how the documentation of those impacts
influenced the decision making process in research and development of pest management. It
is argued that the importance of biological control is now widely felt within the national and
international research community, but that it did not have the same impact on the general
public, the political decision makers and, especially, the donor community.
2. Background
2.1. History of biological control at IITA
The International Institute of Tropical Agriculture (IITA) was founded in 1967 as an
international agricultural institute with a mandate for major food crops, and with ecological
and regional responsibilities to develop sustainable production systems in tropical Africa.
With headquarters in Ibadan, Nigeria, it became the first African link in the worldwide
network of agricultural research centers supported by the consultative Group on International
Agricultural Research (CGIAR), formed in 1971. It conducts agricultural research and
training in partnership with regional bodies and national programs in many parts of subSaharan Africa, addressing crop improvement, plant health, and resource and crop
management within a farming systems framework. Research focuses on small holder
cropping systems on the major food crops: cassava, maize, plantain and banana, yam,
cowpea, and soybean. In 1985, the research station in Cotonou, Benin, was inaugurated. In
1988, in this station, the Centre for Biological Control for Africa was launched. Following
the impressive success of the biological control of the cassava mealybug, the center was also
very successful in establishing biological control of cassava green mite, mango mealybug,
and water hyacinth.
The center was later expanded into a full research division: the Plant Health
Management Division (PHMD). PHMD is dedicated to the development of sustainable plant
protection of primary food crops in Africa, through identification of the ecological
imbalances in the system causing pest problems, and through the development of
environmentally and economically appropriate solutions in collaboration with national
program partners. From classical biological control, the division expanded into new methods,
using entompahtology and biopesticides, within a framework of Integrated Pest Management.
These newer projects have, however, not been subjected to ex post impact assessment and
this paper will, therefore, focus on the impact assessment of the classical biological control
projects.
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2.2. Classical biological control with IITA in Africa
The principles of classical biological control are fairly straightforwards. If a crop is
established in an area separated from its original, it often does not suffer from the pests in the
area of origin. Similarly, natural enemies or diseases of these pests will not occur in the new
areas. If a pest from the home country is accidentally introduced, it is not kept in control by
natural enemies, and the new pests can destroy large parts of the crop. Classical biological
control (as compared to the more recent use of biopesticides), consist of identifying natural
enemies or parasitoids to be introduced in the new zones. To assure these enemies do not
harm the new environment in any unexpected way, they are first studied in quarantaine.
When considered safe to other organisms and the environment, they are mass reared and
released. Once the natural enemy is well established, it reproduces itself in a sustainable way.
Biological control in Africa turned out to be quite successful against cassava mealybug,
cassava green mite, water hyacinth and mango mealybug.
Cassava was introduced to Africa three centuries ago from South America, and
became a major food staple. It was hard hit by two pests introduced accidentally from South
America in the 70s: the cassava mealybug (CMB) and the cassava green mite (CGM). In their
native environment, these pests are kept in control by their natural enemies, which were
absent in Africa. Hence the very rapid spread of the pests and very high losses to the cassava
crop. A natural parasite of the CMB, Epidinocarsis lopezi, a small wasp, was identified, and
mass rearing and distribution techniques developed at IITA (Herren and Neuenschwander,
1991). By the end of the 1980s, the pest was basically under control (Neuenschwander, 1994;
Neuenschwander, 1996).
While CMB was brought under control, the cassava green mite was spreading from East to
West Africa, reaching West Africa in 1979 (Yaninek et al. 1989) and causing heavy losses. A
biological control program was initiated at IITA in 1983, resulting in the identification of a
predator, Typhlodromalus aripo. This natural enemy was successfully imported from South
America, and reared and released in many West African countries (Yaninek et al., 1994),
with a rapid effect on cassava yields.
Another South American pest introduced in West Africa in the 1970s was the water hyacinth,
Eichhornia crassipes (Martius). It was first distributed by gardeners and horticulturists because
of its attractive purple flower, but, due to its extremely fast growth, it soon became the major
floating water weed of the tropical and subtropical regions world wide. Its dense floating mats
hinder fishing and transport; it interferes with the use of water for drinking purposes, irrigation,
and electric power generation; and it affects biodiversity. In the late 1980s it had become a major
pest in the region, especially to the highly productive coastal creek and lagoon systems, from
which many people derive their living, (Julien et al., 1999). To counter the threat of the water
hyacinth on the ecosystems, different types of control methods have been developed, usually
chemical, mechanical, or biological in nature. However, participants in two special international
conferences recognized biological control as the only cost effective, permanent and
environmentally friendly control method. Biological control for water hyacinth has a long history
(Harley, 1990): as an alien invasive plant, it is a prime target for classical biological control, and
at least seven of them have been released for biocontrol in 33 countries (Julien and Griffiths,
1998). Among these, the two weevils, Neochetina eichhorniae Warner and Neochetina bruchi
Hustache (Coleoptera, Curculionidae) were most successful and have been deployed in Africa:
first in Sudan, and subsequently by IITA in Benin and neighbouring countries (van Thielen et al.
1994), and lately around Lake Victoria, leading to a substantial reduction of the water hyacinth
in these countries.
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The latest crop to be ravaged by an introduced pest is the mango, an ancient tree of
Indian origin, now popular all over the tropics for its fruit and shade. In 1986, a new pest
was introduced: the mealybug Rastrococcus invadens Williams (Homoptera:
Pseudococcidae) of South East Asian origin (Williams, 1986). It caused serious damage
to various fruit trees, especially mango, in Benin, Ghana and Togo (Agounké et al.,
1988). In 1987/88, a biological control project was initiated, involving IITA and several
international and national research and development institutes. The parasitic wasp,
Gyranusoidea tebygi Noyes (Hymenoptera: Encyrtidae) was imported from India, studied
in quarantine, reared, released and established in different places in Africa, starting in
1983 (Neuenschwander et al., 1994). Impact of G. tebygi on populations of R. invadens
was demonstrated (Bokonon-Ganta and Neuenschwander, 1995), although reports of
persistent "hot spots" of infestations led to the importation, rearing and release of a
second parasitoid wasp, Anagyrus mangicola Noyes (Hymenoptera: Encyrtidae), starting
in 1991 (Neuenschwander et al., 1994). The successful establishment of this second wasp
brought a further, local reduction of pest populations (Bokonon-Ganta et al., 1996). A
recent study found that the parasitoids are also well established in Nigeria, and that the
populations of the mango mealybug have been greatly reduced (Pitan et al. 2000).
3. Economic analysis of biological control programs
3.1. A general model
To study previous impact assessment methods, it is important to have a general framework to
compare and to draw conclusions. The studies available so far use either cost benefit analysis
or economic surplus. The aim of both techniques is the welfare implications of two or more
situations. In theory, the situation which provides more utility without make people worse off
is preferred. In benefit cost analysis, this utility is approached by the value of the extra
production (or abated loss), and compared to the monetary costs. In classical benefit cost
analysis, the situation with intervention is compared to the situation without intervention, and
compares the differences in benefits to the differences in costs (Gittinger, 1982). Both
benefits and costs accrue over time and result in a series of yearly costs and benefits. Properly
discounted over time, the ratio gives us an idea of the returns to an investment, in this case
the biological control program.
Technically, the impact of a new pest is a shift in the production function: less cassava
can be produced with the same inputs (land, labor, capital, ....). The rational farmer will react
by rearranging his/her inputs to reach an optimum reflecting this new situation. This new
point will not bring the same profit/utility as the old one (or that would have been chosen
before), but it is hard to assume that the lost profit equals the loss in cassava output, at least
not on the long term.
For practical terms, one could consider following general model for the evolution of
the effects of a major pest outbreak (Figure 1). The output Y has dropped from an
equilibrium point Y0 to a low level of Ya , reached at point a. After some adjustment time
(depending on cycle length of crop and available alternatives) starting at point b, a recovery
sets in to reach a new equilibrium at c.
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The economic damage of a major pest outbreak until the new equilibrium can be estimated by
a linear approximation of the area 0abcde, based on the position of points a,b, and c. Both
coordinates (time and value) are needed, as well as a discount factor.
A similar function can be developed for the intervention through a biological control method,
and the difference between the two curves is the yield loss reduction due to the intervention,
represented as the shaded area. After finding the right value for this yield reduction, and the
discount ratio, the benefit of the program can be calculated.
The drawback of using
a supply shift is the
assumption that all
extra production is
valued at the old price.
In practice, the new
equilibrium point will
not only reflect the shift
in the production
function, but also the
change in relative
prices, in funtion of the
Figure 1. Basic model for economic analys of biological
price elasticities. As a
control
result, producers do not
receive all the benefits
of the new technology,
since the extra production is valued lower. Their corrected benefit is called producer surplus.
These benefits accrue to the consumers: they can consume more at lower prices. Consumer
and producer surplus add up to economic surplus and methods have been developed to
quantify them (Alston et al., 1995). These methods are becoming increasingly popular for
impact analysis, and special software has recently been developed.
3.2. Cassava mealybug
The first economic analysis of biological control in Africa concerned the cassava mealybug
(Norgaard, 1988). The author visited IITA as a consultant and extrapolated the limited
available data for West Africa to the whole affected region. He assumed a tapering off effect
(Figure 2) based on establishment of natural enemies, in the case of no biological control.
Alternative strategies by farmers were, however, not taken into account. Over a period of 25
years, the discounted benefits were estimated at US$ 2.2 billion, and the expenditures at 14.8
million, leading to a benefit cost ratio of 149. The author concludes that this is an unusually
successful project.
Over the years, much more data on the effect of CMB on yield, and the crop loss abatement
from biological control, became available. A more recent study (Zeddies et al., 2001)
incorporated the data from 27 countries, and extrapolated over 40 year time period. They
rejected the tapering off of Norgaard, stating that there was no evidence of emerging
indigenous natural enemies, and assumed a constant benefit over the years.. The benefits in
6
the basic scenario were estimated at US$ 9.4 billion, compared to a cost of US$ 47, leading to
a benefit cost ration of 430. Even under the most pessimistic scenario, the project remains
highly profitable. The analysis did not take into account farmers’ alternative strategies such
as shifting to new crops, and no shift in prices or consumer surplus were analyzed.
3.3. Mango Mealybug
The impact of the biological control of mango mealybug in Bening was assessed, through a
survey of mango producers in the affected areas (Bokonon-Ganta et al. forthcoming). Most
producers attributed the observed improvement of mango production to the success of
biological control. Based on production estimates by producers, the negative impact of the
pest on plant production and the positive impact of the introduced natural enemy were
demonstrated. Interviewed mango producers gained on average $328 per year by the
biological control programme. Extrapolated to all producers of Benin, a yearly gain of $50
million in mango production can be estimated. The present value of accrued benefits is
estimated at $531 million over a period of 20 years. The total cost of the biological control of
mango mealybug is estimated at $3.66 million, which includes initial costs in other African
countries and the introduction of the natural enemy from India, resulting in a benefit-cost
ratio of 145:1 for benefits in Benin alone. In this analysis, tapering off of the benefits to
alternative strategies was incorporated, but not consumer surplus.
3.4. Water hyacinth
The impact of the biological control program of water hyacinth was assessed through a
survey in Benin in 1999 (De Groote et al, 2002). This survey, the first undertaken specifically
to assess impact, interviewed a representative sample of men and women from 192
households in 24 villages in the target area, using participatory and quantitative methods.
Results revealed that water hyacinth, although not eliminated, was perceived by the villagers
as having been reduced from a serious pest to one of minor or moderate importance.
According to their estimates of the impacts they perceived, at the peak of the infestation
water hyacinth had reduced the yearly income of this population of about 200,000 by about
US$ 93 million per year. Lost revenues for men were mostly in fishing, while women
experienced lost revenues in trade, in particular of food crops and fish. The reduction of
water hyacinth cover through biological control was credited with an increase in income of $
32.6 million per year. The total cost of the control program is estimated at a present value of
$ 2.09 million. Assuming the benefits are to stay constant over the next 20 years, a most
conservative assumption, the accumulated present value would be $ 311 million., yielding a
respectable benefit cost ratio of 149:1. This ratio is calculated for southern Benin alone, and
does not take into account the benefits of the project to other countries were the biological
control agents were successfully introduced. No consumer surplus was included, since the
fish production of the affected area is small compared to the national production. No tapering
off was incorporated either, since no alternative strategies against water hyacinth have been
found effective.
3.5. Cassava green mite
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Finally, impact assessments have been carried out to evaluate the effectiveness of the
biological control of cassava mealybug in Benin, Ghana, and Nigeria (Coulibaly, 2002).
This study is the first to use an economic surplus model. The results show that biological
control of CGM has very substantial economic returns, hence gains to both cassava
producers and consumers. The estimated discounted economic returns expressed as Net
Present Values (NPV) at a discount rate of 10% for the period 1983 – 2020 are about
$1,700 million ($301/ha/year) in Nigeria, $383 million ($336/ha/year) in Ghana, and $74
million ($206/ha/year) in Benin. The Internal Rates of Return (IRR) or break-even discount
rates are substantially higher than for most public investments: 111% in Ghana, 125% in
Nigeria and 101% in Benin. Sensitivity analysis shows that returns to biological control of
CGM are still very important even under a higher discount rate of 15% or under lower
yield gains. The results clearly demonstrate again that investing in classical biological
control is highly profitable and is an economically rational alternative to other forms of
pest control in sub-Saharan Africa. The analysis uses economic surplus methods, but the
assumptions on yield reduction and tapering off of the effects are not clearly presented in
the paper.
6. Other impact of biological control programs
In the above studies, only direct impact on production was measured: abated crop loss,
fisheries, and transport. However, this is at best an uderestimation of the benefits. Other
benefits include environmental and institutional benefits. Although not quantified, they need
mentioning.
Environmental benefits arise increase of the quality of the environment. A first benefit
from biological control is a reduction in the use of pesticides and improvement of health.
Although these benefits have been shown to be substantial in Asia (Pingali et al., 1994), the
general consensus is that pesticide use for food crops is so low in Africa that these benefits
can be neglected, with the exception of locust control (Houndekon et al., 1998). Other
important environmental benefits are water quality in the case of water hyacinth (De Groote
et al., 2002), and shade from mango trees (Bokonon-Ganta, 2002). Unfortunately, benefits to
the environment is only documented with anecdotal evidence, but not calculated in monetary
terms, because of lack of resources.
A second important extra benefit of the biological control programs was institutional.
The search for natural enemies in the original home of the pests, as well as their importation,
rearing, release and monitoring were executed in collaboration with the national quarantine
and research organizations, which were prepared through workshops and conferences, and
who participated as full scientific collaborators. This left a cadre of well-educated and often
well equipped scientists, who were capable of collaborating in the next project, executing
projects on their own, and influencing the public opinion. Again, these impacts were not
systematically analyzed.
7. Impact of impact studies
Over the years, impact assessment has gained importance in IITA and PHMD. Where in the
beginning, consultants would be invited to assess ex post impact, there is an increased interest
in having in-house social scientists do the research. After the initial positive results of the
Norgaard study, it took many years before new impact studies were undertaken. Economists
8
were only hired in PHMD in the late 1990s, and their work was initially more to prepare the
feasibility of new projects such as the biopesticides against grasshoppers and locusts (De
Groote et al. 2001, Mueller et al., forthcoming). More recently, their input for the ex post
impact assessment was led to the studies on water hyacinth, mango mealybug and cassava
green mite. Due to lack of funds, however, only one social scientist is currently working in
the division. Current policy, as presented in the Strategic Plan of 1999, has impact assessment
explicitly incorporated in all activities. It is seen as a continuum, that takes place during all
phases of a activity, and for several years afterwards (Manyong et al., 2000). Emphasis is put
on Participatory Impact Assessment, and new approaches are being developed such as the
“follow the technology” method (Douthwaite et al. 2001). For quantitative analysis social,
economic and environmental indicators are being collected. Impact assessment is organized
within one of the six IITA projects (Assessing Impact, Formulating Policy Options, and Systems
Analysis).
Concerning biological control, alhtough the results of the impact show that these projects
present very sustainable solutions and are clearly highly profitable, its profile with donor
agencies is rather low. Some of the reasons presented here are the lack of guarantee for a
sustainable solution from the outset, the long time frame required, the limited potential for
collaboration with the private sector, and the lack of visibility and related public awareness.
For these reasons, biological control and IPM are often not given their share of recognition
within the CGIAR system and the donor community.
8. Conclusions: You can lead a horse to the water, but you can not make it drink
Impact assessment is receiving increasing attention within IITA and PHMD. This attention
can partly be attributed to an increased request for accountability of the donor community,
the reduction of funds available for agricultural research, and, maybe, the results of studies
such as those presented here. General principles are now widely established, although
methods are still being developed. Methodologies need improvement and standard
established, so that the results can be compared. Moreover, the results need to be scrutinized
by publication in refereed journals.
To improve the quality of impact assessment and its contribution to make biological
control more efficient, it is therefore recommended that biological control and IPM projects
include an impact assessment component from the beginning. This will help guide the
development of the technology and document the potential impact from the start. Further,
more effort is needed to bring the impact of biological control to the attention of the general
public and the donor community.
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