Abstract:
Arabica coffee Coffea arabica L. is an important cash crop supporting millions of households in East Africa. However, the crop faces challenges of infestation by some insect pests that lead to substantial economic loss and lower quality of beans. The Antestia bugs, Antestiopsis spp. (Hemiptera: Pentatomidae), the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae: Scolytinae) and the African coffee white stem borer, Monochamus leuconotus (Pascoe) (Coleoptera: Cerambycidae) are major insect pests threatening coffee production in Africa. Nevertheless, the developed control measures against these pests are not effective to control their damages in coffee plantations. This is a consequence of the insufficient knowledge of their biology, ecology and distribution as influenced by environmental factors. Therefore, the objectives of this study were to: i) provide the thermal requirements for the development of immature stages of H. hampei and M. leuconotus by modelling their life history traits as influenced by temperature, ii) describe the seasonal variation of Antestiopsis thunbergii and A.facetoides populations and identify the factors that affect their populations over time and space, and iii) predict future distribution of A. thunbergii as influenced by emperature rising over elevation gradients using field observations and emperature-dependent development models. Life history traits of both H. hampei and M. leuconotus were studied at seven constant temperatures in the range 15-35°C. Linear and nonlinear models were fitted to the development and survival data for both pests in order to calculate their thermal thresholds. In addition, nonlinear models were fitted to M. leuconotus fecundity and adult senescence, compiled and used to simulate the population growth. The seasonal variation of both A. thunbergii and A. facetoides was assessed for two years on coffee farms located on the Aberdare range, in Kenya. Future distribution for A. thunbergii up to the year 2055 was predicted over elevation gradients in the range 1000-1700 m asl, on Mt. Kilimanjaro, Tanzania using the life history traits of the pest and climatic data. Thermal thresholds (𝑇𝑚𝑖𝑛 and 𝑇𝑚𝑎𝑥) for H. hampei immature stages development ranged between 10.5 and 35.2°C, with development time ranges of 4.6-16.9, 11.6-39.5 and 3.0-13.6 days for the egg, larva and pupa, respectively. On the other hand, the thermal window for M. leuconotus immature development was estimated between 10.0 and 40.0°C, with an optimum temperature for survival in the range 23.0-23.9°C. The highest fecundity for M. leuconotus was 97.8 eggs per female at 23°C. Simulated life table parameters showed the highest net reproductive rate Ro of 11.8 per female at 26°C. The intrinsic rate of increase rm was higher between 26 and 28°C, with a value of 0.008. The seasonal variation of A. thunbergii and A. facetoides showed that both species had a similar trend with the highest infestation being reported between the months of June and August. The availability of food (green berries) was that most crucial factor that determined these seasonal variations. Future prediction of A. thunbergii showed that the distribution of the risks of infestation by this pest will be higher at the highest elevations (1500-1800 m asl)and A. thunbergii will follow the shift of the coffee production areas to the highest elevations. These findings will help to better understand coffee pests’ distribution and dynamics in coffee plantations and inform decision makers on the risks of these pests under changing climate. This will contribute to a more efficient and sustainable management strategy for coffee insect pests in Africa.