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1. A Temperature-Based Phenology Model for Predicting the
Development, Fecundity, and Life Table Parameters of the
African Sweetpotato Weevil, Cylas puncticollis
J. Okonya, N. Mujica, P. Carhuapoma & J. Kroschel
DCE Crop Systems Intensification and Climate Change (CSI-CC)

2. Outline
Introduction
 Predicted climatic changes for East Africa
 Effects of climate change on sweetpotato crop and insect pests
 Cylas puncticollis: the major sweetpotato pest in Africa
 Study approach and objectives
Methods
 Life table experiments
 Phenology modeling using the ILCYM software
Results
 Temperature effects on biology
 Life-table studies
Conclusions

3. Predicted climatic changes for E. Africa
IPCC report, 2013
 Temperatures changes
 0.5 - 1.2 oC by 2035
 1.0 - 2.4 oC by 2065
 1.0 - 3.1 oC by 2100
 Effects of increased temperatures
 Reduced yields in cereals and coffee
 Increased pest and disease pressure on crops and livestock
 Changes in precipitation
 -5 – 10% by 2035
 -6 – 17% by 2065
 -7 – 21% by 2100
 Effects of changes in precipitation
 shorter rainy seasons
 Extreme events (El Niño)
 Increased runoff and evaporation
 Floods

4. Effects of climate change on sweetpotato production

5.  Increased yield losses caused by pests and
diseases
 Shortage of planting materials after a
prolonged dry season
 Opportunities for sale of vines (commercial
seed systems)
 Shorter maturity time in the highlands, more
food
 Longer/more cropping seasons in semi-arid
zones or all the time in lowlands
Effects of climate change on sweetpotato production
Sale of vines as seed and fodder
Swampland with water all the time
Clean roots and Cylas infested roots
Negative effects
Positive effects

6. Effects of climate change on insect pests
 Range expansion and invasion by
new pests.
 Faster pest development
 Negative effects on beneficial
insects leading to pest outbreaks
 Minor pests may develop into
major pests
 Increase damage by invasive
species such as the Tuta absoluta
 drought stressed plants are more
susceptible to pest damage
(adapted from Padgham, 2009; Discussion paper - The World Bank)

7. Geographical distribution
Adult C. puncticollis
Larval root damage
Distribution of C. puncticollis in countries of Africa; red points indicate
geo-referenced occurrences.
Burundi, Cape Verde,
Cameroon, Chad, Congo,
Central African Republic,
DR Congo, Ethiopia,
Ghana, Ivory Coast,
Kenya, Madagascar,
Malawi, Mali,
Mozambique, Nigeria,
Senegal, Sierra Leone,
Somalia, Sudan,
Tanzania, Uganda,
Rwanda, and Zambia

8. Study approach and objectives
 We hypothesised that increased temperatures due to global warming
will increase the spread and damage potential of C. puncticollis.
 Conduct life table studies under different temperature regimes and
develop phenology models using Insect Life Cycle Modeling (ILYCM)
software
(https://research.cip.cgiar.org/confluence/display/ilcym/Home)
The modeling results will inform policy makers about future
pest risks and improve adaptation planning of integrated pest
management

9. Materials & Methods
 Incubators at constant temperatures: 12.5,15,
17.5, 20, 25, 30, 35, 40 and 42.5 oC
 A data logger to monitor temperature and RH:
60-80%
 Parameters to be recorded
 Development time for eggs, larvae and
pupae
 Mortality of eggs, larvae and pupae
 Fecundity: No. of eggs/female/day
 Adult longevity (days) for males and
females

10. Insect rearing and life table studies
NASPOT 1 sweetpotato roots used
for feeding C. puncticollis
Containers with a single insect in the
incubator at a constant temperature
Mass rearing of C. puncticollis on sweetpotato roots
Adult C. p feeding on
a sweetpotato cube

11. Temperature effects on CP biology
Temp
(oC)
Mean development time ± SE (days) Adult longevity ± SE (days)
Egg Larva Pupa female male
12.5 - NA NA NA NA
15 20.16 ± 0.29
a (32)
- NA NA NA
17.5 9.87 ± 0.17 b
(97)
65.32 ± 2.79 a
(19)
15.65 ± 0.49 a
(17)
64.38 ± 16.53
a (8)
37.00 ± 14.060
b (9)
20 6.00 ± 0.05 c
(201)
36.61 ± 1.12 b
(46)
8.94 ± 0. 0.26
b (33)
71.39 ± 13.39
a (18)
55.87 ±11.06
ab (15)
25 4.00 ± 0.005
d (116)
13.14 ± 0.19 c
(97)
4.75 ± 0.10 c
(95)
84.10 ± 15.12
a (29)
74.95 ± 9.71 a
(66)
30 3.12 ± 0.03 d
(103)
10.21 ± 0.08 d
(86)
3.07 ± 0.08 d
(85)
62.47 ± 9.07
ab (38)
49.38 ±7.61 ab
(47)
35 3.00 ± 0.00 d
(104)
9.80 ± 0.19 d
(88)
2.72 ± 0.05 d
(81)
26.62 ± 5.41 b
(37)
42.18 ± 5.987
ab (44)
40 3.57 ± 0.06 d
(67)
- NA NA NA
42.5 - NA NA NA NA
Mean development time and adult longevity of C. puncticollis

12. Temperature effects on CP biology – Mortality rates
Temperature-dependent mortality rates of eggs, larvae
and pupae for C. puncticollis at constant temperatures
Temp
(oC)
Mortality rates (percent)
Egg Larva Pupa
12.5 100 (300) - -
15 68 (100) 100 (32)
17.5 34 (147) 80 (97) 11 (19)
20 2 (205) 77 (201) 28 (46)
25 1 (117) 16 (116) 2 (97)
30 0 (103) 17 (103) 1 (86)
35 16 (124) 15 (104) 8 (88)
40 39 (110) 100 (67)
42.5 100 (300) - -

13. Temperature effects on CP biology- Fecundity
Temperature-dependent total C. puncticollis egg production curves. Fitted curve: Gaussian model;
dashed lines represent the upper and lower 95% confidence intervals; dots are observed mean
values
Gaussian model
Temp
(oC)
Total oviposition per
female ± SE (eggs)
15 0 d (62)
17.5 6.16 ± 1.96 cd (50)
20 37.51 ± 9.31 c (43)
25 235.13 ± 42.82 b (15)
30 335.27 ± 37.68 a (15)
35 14.71 ± 4.06 cd (31)
40 0 d (31)

14. 0
0.02
0.04
0.06
0.08
0.1
0.12
20 22 24 26 28 30 32 34 36
Intrinsicrateofincrease,(rm)
(Females/female/day)
Temperature (°C)
0.98
1
1.02
1.04
1.06
1.08
1.1
1.12
1.14
20 22 24 26 28 30 32 34 36
Finiterateofincrease,λ
(Females/female/day)
Temperature (°C)
0
20
40
60
80
100
120
20 22 24 26 28 30 32 34 36
Grossreproductionrate,GRR
(Females/female)
Temperature (°C)
0
10
20
30
40
50
20 22 24 26 28 30 32 34 36
Netreproductionrate,Ro
(Females/female)
Temperature (°C)
0
20
40
60
80
100
120
140
20 22 24 26 28 30 32 34 36
Meangenerationtime,T(days)
Temperature (°C)
0
20
40
60
80
100
120
140
160
20 22 24 26 28 30 32 34 36
Doublingtime,Dt(days)
Temperature (°C)
A B
C D
FE
Lifetable parameters for C. puncticollis
rm = 0.11, 29-31 °C
GRR = 110.95, 28 °C Ro = 45.95, 28.5 °C
T=121d at 21.5 °C &
T= 29 days at 33-35.5 °C
Dt = 138d at 21.5 °C &
Dt = 6d at 29.5-30.5 °C
λ = 1.12 at 30 °C

15. Conclusions
 Temperature will have direct effects on C. puncticollis biology and
development
 Faster pest development in warm lowland will result in 100% C.
puncticollis damage
 At 30 to 35 °C, C. puncticollis has a high capacity for rapid population
increase due to its high intrinsic rate of natural increase.
 This information was used in Pest Risk Analysis (PRA) to predict the risk
of establishment, and abundance by the 2050
 Fore instance, C. puncticollis is predicted to spread of to higher altitude
areas (range expansion) by the 2050

16. Acknowledgement
For more information
Kroschel et al. (2016): Pest Distribution and Risk Atlas for Africa- Potential global and regional distribution
and abundance of agricultural and horticultural pests and associated biocontrol agents under current and
future climates. International Potato Center (CIP), Lima, Peru, 650pp (in press).
Joshua Okonya j.okonya@cgiar.org
www.cipotato.org/ilcym
Thank you