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. 2015 Jun 15;10(6):e0130427.
doi: 10.1371/journal.pone.0130427. eCollection 2015.

Predicting the Impact of Temperature Change on the Future Distribution of Maize Stem Borers and Their Natural Enemies along East African Mountain Gradients Using Phenology Models

Sizah Mwalusepo  1 , Henri E Z Tonnang  2 , Estomih S Massawe  3 , Gerphas O Okuku  4 , Nancy Khadioli  4 , Tino Johansson  2 , Paul-André Calatayud  5 , Bruno Pierre Le Ru  5
Affiliations

Predicting the Impact of Temperature Change on the Future Distribution of Maize Stem Borers and Their Natural Enemies along East African Mountain Gradients Using Phenology Models

Sizah Mwalusepo et al. PLoS One. .

Abstract

Lepidopteran stem borers are among the most important pests of maize in East Africa. The objective of the present study was to predict the impact of temperature change on the distribution and abundance of the crambid Chilo partellus, the noctuid Busseola fusca, and their larval parasitoids Cotesia flavipes and Cotesia sesamiae at local scale along Kilimanjaro and Taita Hills gradients in Tanzania and Kenya, respectively. Temperature-dependent phenology models of pests and parasitoids were used in a geographic information system for mapping. The three risk indices namely establishment, generation, and activity indices were computed using current temperature data record from local weather stations and future (i.e., 2055) climatic condition based on downscaled climate change data from the AFRICLIM database. The calculations were carried out using index interpolator, a sub-module of the Insect Life Cycle Modeling (ILCYM) software. Thin plate algorithm was used for interpolation of the indices. Our study confirmed that temperature was a key factor explaining the distribution of stem borers and their natural enemies but other climatic factors and factors related to the top-down regulation of pests by parasitoids (host-parasitoid synchrony) also played a role. Results based on temperature only indicated a worsening of stem borer impact on maize production along the two East African mountain gradients studied. This was attributed to three main changes occurring simultaneously: (1) range expansion of the lowland species C. partellus in areas above 1200 m.a.s.l.; (2) increase of the number of pest generations across all altitudes, thus by 2055 damage by both pests will increase in the most productive maize zones of both transects; (3) disruption of the geographical distribution of pests and their larval parasitoids will cause an improvement of biological control at altitude below 1200 m.a.s.l. and a deterioration above 1200 m.a.s.l. The predicted increase in pest activity will significantly increase maize yield losses in all agro-ecological zones across both transects but to a much greater extent in lower areas.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. The study areas: (A) Mount Kilimanjaro transect, (B) Taita hills transect.
The circles indicate the locations where the data loggers for the climate data collection have been installed along the altitudinal gradients.
Fig 2
Fig 2. Change in the establishment, abundance and activity indices of C. partellus and C. flavipes along the Mount Kilimanjaro transect; C. partellus current distribution, (A) (ERI), (B) (GI), (C) (AI); C. flavipes current distribution (D) (ERI), (E) (GI), (F) (AI); absolute establishment index change between 2013 and 2055, (G) C. partellus, (H) C. flavipes; (K) C. partellus and C. flavipes synchrony under future climate for the establishment index between 2013 and 2055.
ERI = Establishment Index, GI = Generation Index, AI = Activity Index.
Fig 3
Fig 3. Change in the establishment, abundance and activity indices of B. fusca and C. sesamiae along the Mount Kilimanjaro transect; B. fusca current distribution, (A) ERI, (B) GI, (C) AI; C. sesamiae current distribution (D) ERI, (E) GI, (F) AI; absolute establishment index change between 2013 and 2055, (G) B. fusca, (H) C. sesamiae; (K) B. fusca and C. sesamiae synchrony under future climate for the establishment index between 2013 and 2055.
ERI = Establishment Index, GI = Generation Index, AI = Activity Index.
Fig 4
Fig 4. Change in the establishment, abundance and activity indices of C. partellus and C. flavipes study along the Taita hills transect; C. partellus current distribution, (A) (ERI), (B) (GI), (C) (AI); C. flavipes current distribution (D) (ERI), (E) (GI), (F) (AI); absolute establishment index change between 2013 and 2055, (G) C. partellus, (H) C. flavipes; (K) C. partellus and C. flavipes synchrony under future climate for the establishment index between 2013 and 2055.
ERI = Establishment Index, GI = Generation Index, AI = Activity Index.
Fig 5
Fig 5. Changes in the establishment, abundance and activity indices of B. fusca and C. sesamiae study along the Taita hills transect; B. fusca current distribution, (A) ERI, (B) GI, (C) AI; C. sesamiae current distribution (D) ERI, (E) GI, (F) AI; absolute establishment index change between 2013 and 2055, (G) B. fusca, (H) C. sesamiae; (K) B. fusca and C. sesamiae synchrony under future climate for the establishment index between 2013 and 2055.
ERI = Establishment Index, GI = Generation Index, AI = Activity Index.
Fig 6
Fig 6. Absolute generation index changes between 2013 and 2055; Mount Kilimanjaro transect.
(A) C. partellus and C. flavipes; (B) B. fusca and C. sesamiae; Taita hills transect, (C) C. partellus and C. flavipes, (D) B. fusca and C. sesamiae.
Fig 7
Fig 7. Minimum and maximum temperatures curves for current (2013) and future (2055); (A) Miwaleni (764 m.a.s.l); (B) Marua (1683 m.a.s.l) along Mount Kilimanjaro transect; (C) Kipusi (832 m.a.s.l); (D) Vuria (1800 m.a.s.l) along Taita hills transect.
Bars above the x-axis indicate the maize-cropping season and oval indicates the starting of rainy season.
Fig 8
Fig 8
Finite rate of increase for current (2013) and future (2055) throughout the year, at two local weather stations along Mount Kilimanjaro transects; (A) C. partellus and C. flavipes; (B) B. fusca and C. sesamiae at Miwaleni (764 m.a.s.l); (C) C. partellus and C. flavipes; (D) B. fusca and C. sesamiae at Marua (1683 m.a.s.l).
Fig 9
Fig 9
Finite rate of increase for current (2013) and future (2055) throughout the year, at two local weather stations along Taita hills transects; (A) C. partellus and C. flavipes; (B) B. fusca and C. sesamiae at Kipusi (832 m.a.s.l); (C) C. partellus and C. flavipes; (D) B. fusca and C. sesamiae at Vuria (1800 m.a.s.l).
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This research was conducted under the Climate Change Impacts on Ecosystem Services and Food Security in Eastern Africa (CHIESA) project. CHIESA is funded by the Ministry for Foreign Affairs of Finland.