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Research proposal for PhD student
The international Centre of Insect Physiology and Ecology (icipe) and its partners are seeking a PhD
student to conduct research on the future effects of global warming on cereal stem borers and related
natural enemies in East Africa. He/she will be based at icipe Headquarters in Nairobi, Kenya.
Research proposal title:
Predicting climate change induced vulnerability of cereal crops to Busseola fusca and Chilo spp.
and their main natural enemies through advanced insect phenology modelling
Hypothesis:
Climate changes will modify the stem borer communities in cereal crops by both reduction and
expansion of the present distribution of stem borer species, modify the interactions with their specific
natural enemies, affect stem borer abundance and severity and most likely lead to higher yield losses
and lower grains quality.
Research background
Climate change and impact on African agriculture
Today, it is widely accepted that the Earth’s climate has become increasingly warmer, most likely
due to increasing greenhouse gas emissions. Climate change is expected to exacerbate the already
serious challenges to food security and economic development, especially on the African continent
where people are already struggling to meet challenges posed by existing climatic variability (IPPC
2007, Slingo et al., 2005). A total of 330 million people live in extreme poverty in sub-Saharan Africa
with 70 % of the population surviving by subsistence agriculture (Hellmuth et al., 2007). The
agricultural sector is a major contributor to the current economy of most African countries ranging
from 10 % to 70 % of the gross domestic product (GDP) with the slowest record of productivity
increase in the world. Climate change is likely to reduce agriculture’s share of GDP (Mendelsohn et
al. 2000), e.g., crop productivity will be greatly affected in Africa and overall yields such as for maize
may fall by 10 to 20 % by the year 2055 because of warming and drying (Jones and Thornton 2003,
Thornton et al. 2006). Adaptation to climate change seems to be especially relevant for Africa
(Thomas & Twyman, 2005) and climate derived information is most likely to improve development
outcomes when it is integrated into a framework for decision making to specific risks (Hellmuth et
al., 2007).
Effect of climate change on arthropod pests and pest-natural enemy interactions
On average, 30 to 50% of the yield losses in agricultural crops are caused by insect pests (Oerke
et al. 1994). Climate, especially temperature, has a strong and direct influence on insect development,
reproduction and survival (Andrewartha and Birch 1955, Uvarov 1931) and is considered under
climate change the dominant abiotic factor directly affecting herbivorous insects (Bale et al. 2002).
Since insect population growth potentials are mainly temperature driven, a rise in temperature may
either increase or decrease insect development rates and related crop damages depending on the insect
species optimum temperature range.
Depending on the complexity and species richness, agroecosystems can have a good potential to
provide a high level of natural biological control, and hence ecosystem complexity can increase
ecosystem resilience to pest outbreaks. However, little is known on how climate change may affect
icipe – African Insect Science for Food and Health
P. O. Box 30772-00100 Nairobi, Kenya
Phone: +254 20 8632000; Fax: +254 20 8632001/2
[email protected]
www.icipe.org
multitrophic levels or competitive interactions. Recent studies indicate that climate change can
dissociate predator-prey relationships, because of a higher sensitivity of higher trophic levels to
climatic variability or of different temperature optima compared with pests (Voigt et al. 2003). In this
respect, divergences in the thermal preferences of the pest and its natural enemy will lead to a
disruption of the temporal or geographical synchronization, increasing the risk of host outbreaks
(Hance et al. 2007). Additional negative effects might be a decrease in the fitness of natural enemies
due to changes in herbivore quality and size induced by temperature (Thomson et al. 2009). As a
result, these authors suggested a careful analysis on how host-natural enemy systems react to changes
in temperature to predict and manage the consequences of global change at the ecosystem level. This
might negatively affect successful classical biocontrol programs, in which an increase in temperature
could give a comparative advantage to the pest population growth compared with its biocontrol agent.
Rational of the PhD research project
The most damaging field pests of cereals in sub-Sahara Africa (SSA) are lepidopteran stem and
ear borers, most of them belonging to the families Noctuidae, Pyralidae and Crambidae (see overview
by Polaszek, 1998). Most often, these borers occur as a complex of species with overlapping spatial
and temporal distributions.
In East and Southern Africa, B. fusca and C. partellus are the predominant cereal stem borers.
B. fusca is mainly a pest in the mid-altitude/highland zones where temperatures are lower than in the
humid lowland tropics (Zhou et al, 2002; Ong’amo et al., 2006). The exotic crambid Chilo partellus
(Swinhoe) is mainly found in the warmer lowland areas whereas Sesamia spp. are uncommon (Zhou
et al, 2002; Ong’amo et al., 2006). Both B. fusca and C. partellus go into facultative diapause during
the off season. (Le Ru, unpubl. data).
Chilo partellus (Swinhoe) and Chilo orichalcociliellus Strand (Lepidoptera: Crambidae) are
gramineous stem borers that occur sympatrically in the coastal area of ESA. Observations over the
past 40 years (until end of year 90’s) indicate that the indigenous stem borer, C. orichalcociliellus,
was gradually displaced by the exotic stem borer, C. partellus. Zhou et al. (2001) argued that the
shorter developmental period of C. partellus may give this species a competitive advantage over the
slower developing C. orichalcociliellus. However, recent findings showed that both species coexist
and their populations are at equilibrium (Jiang et al., 2006). More recent surveys data reveal that
Chilo species can also be found in mid and high land. But there is no data on the movement of their
parasitoids.
The most important natural enemies of B. fusca identified so far in EAS is Cotesia sesamiae.
Previous work has shown that two biotypes of C. sesamiae occur in Kenya which express differential
abilities to develop in B. fusca. A biotype from western Kenya successfully develops in B. fusca,
while a biotype from the eastern coastal area not (Mochiah et al., 2002). Raisons for this different
behavior are now well documented, involving endosymbiotic viruses (polydnavirus or PDV) (Dupas
et al., 2008) and Wolbachia (endocytoplasmic bacteria) (Branca, 2009).
Chilo partellus, is the only invasive stem borer and at the same the most damaging pests of maize
and sorghum in lowland agroecological areas in ESA. Since beginning of years 90’s it has started to
expand his distribution into the cooler mid and high elevation areas of ESA because of competitive
advantages againsts B. fusca ( Kfir, 1997; Zhou et al., 2002; Ong’amo et al., 2006).
Thus, the abundance and distribution of stem borer pests and their main natural is expected to
vary considerable with climatic variability. However, this may vary depending on the flexibility of
their life-history characteristics, interaction with their respective host-plant and other species
(competition, predation and parasitism). Some species are expected to shift their distributions by
expanding into the new areas, while others shift their habitats and host-plant preferences (Thomas et
al. 2001), or under go local extinction. Changes in stem borer distribution and host shifts are not new
in Africa as it has been reported in the recent past (Zhou et al., 2001; Assefa et al, 2009). However,
these changes will in turn affect the existing community structure and the general species
composition.
Objectives
Climate has a direct influence on insect development, reproduction and survival (Basle & Al,
2002) and any increase in temperature will have a direct effect in various aspects of their life cycle
and ecology. The objectives of this research are:
a) to predict with life table data the influence of the expected climate changes on i) the stem
borer communities and their natural enemies in cereal crop (potential geographic shifts,
competition,….)
b) to collect and collate more data on stem borer and their natural enemies in cereal crops from
different agroecological areas to validate the prediction generated with the previous data.
Materials and methods
Materials
Maize (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench) are among the important
cereal crops in Africa (Bosque-Pérez & Schulthess, 1998). Stem borers are also found on wild grasses
along road side and around field crops.
Methods
Innovative insect phenology modeling and risk mapping in a Geographic Information Systems
(GIS) environment will be used to assess future impacts of climate change on agricultural pests.
Process-based phenology models that use a number of functions describing temperature-driven
processes, like development, mortality, reproduction, etc. in insect species, will be developed. A
cohort up-dating algorithm and rate summation approach will be used for simulating
multidimensional age and stage structured populations. Input data are minimum and maximum daily
temperature (real or interpolated data). Simulation results, like life-table parameters (i.e. net
reproduction rate, mean generation time, intrinsic and finite rate of increase, and doubling time), can
be plotted over time; for analysis of the pests’ risk in space three generic risk indices (Index for
Establishment, Generation number, and Activity Index) can be visualized in GIS maps. The functions
and parameters for a given phenology model will be determined based on existing literature data and
insect life-table studies carried out over a range of temperatures.
Models will be produced with a current version of Insect Life Cycle Modeling (ILCYM) software
developed by CIP (Version 2.0). ILCYM software provides a “model builder” for facilitating
determination of the equations used and compilation of the final model, and analysis tools for
validating established models by comparing simulation results with field-derived life-table data. To
assess pest-natural enemy interactions two-species-interaction models will be developed. GIS tools
implemented into the ILCYM software will be used to produce risk maps. Regional and national scale
simulation will be based on WorldClim data or other data sets, including real or historical data, which
provide higher accuracy and allow further downscaling. To forecast the pests’ risk under climate
change scenario maps will be generated using temperature forecasts from an atmospheric general
circulation model (GCM), described by Govindasamy et al. (2003), which is currently implemented
in ILCYM software; however, the GCM can be exchanged if required. The process-based modeling
approach allows for integration of further biotic or abiotic factors ruling on pest populations (e.g.,
precipitation, management practices and their effects on specific life stages of the pest, etc.). These
factors are pest specific and require additional experiments for model parameterization and their
integration into the overall model. ILCYM software will be further improved during the course of the
project to better meet the requirements of the different stakeholders (research, extension, decision
support for IPM practices).
Activities and Time frames
Activity 1 Bibliography: Synthesis of the already available life table and distribution data on the key
stem borers and their natural enemies; collection of meteorological data. (1st quarter of
the first year)
Activity 2 Establishment of the past (with data already available from WAU project, NSBB project)
and current (survey will be carried out in Kenya targeting 4 different agroecological areas
characterized with different stem borer pest and parasitoid community structures)
distribution and severity of targeted stem borer pests and, distribution and efficacy of
parasitoids. Understand farmers’ knowledge and coping strategies to control pests (First
year)
Activity 3 Establishment of life-tables of the different stem borer pests and parasitoids under
controlled temperature in laboratory conditions and under natural conditions in four
localities belonging to different agroecological areas (First and second years)
Activity 4 Modeling the stem borer pest distribution with phenology models and their potential to
increase infestation and to expand present distribution due to global warming determined.
Modeling the parasitoid distribution and the link with pest distribution models (pestparasitoid interactions) with phenology models and risk maps (Second year)
The third year of the PhD will serve to complete the activities and the write up of the thesis
manuscript.
Qualification requirements for applying candidates:
Applicants must have a M.Sc. in Ecology with experience in insect related research or a M.Sc. in
Entomology with experience in ecology and spatial analysis. The successful applicants should have a
strong foundation in quantitative analysis, experience and use of temperature-based phenology
models. The successful applicants must also have a proven track-record of R&D relating to growth
and spatial analysis models and demonstrated ability to publish in high quality peer-reviewed
scientific journal. He/she should have outstanding oral and written communication skills.
Main Supervisor (University)
Other supervisors proposed:
Dr. A. Chabi-Olaye ([email protected] ); 2Dr. Bruno Le Rü ([email protected] )
1
Noctuid Stem Borer Biodiversity Project (NSBB), Biodiversity Program, Institut de Recherche pour
le Développement (IRD) c/o International Centre of Insect Physiology and Ecology (icipe). P. O. Box
30772, Nairobi, (Kenya) and Institut de Recherche pour le Développement (IRD) c/o Centre National
de la Recherche Scientifique (CNRS), Laboratoire Populations, Génétique et Evolution, Bât. 13, B.P.
1, 91198 Gif-sur-Yvette cedex (France).
Funding
Financial support is available for three years. Employment conditions include an attractive
remuneration package, including health care, home leave, and other benefits.
Application
Kindly send applications with a motivation letter, a CV and the names and contact information of
three referees by email before 26th February, 2010 to the proposed supervisors.