Predicting the effect of global warming on the future potential distribution and abundance of the African sweet-potato weevil CylaspuncticollisBoheman
Joshua Sikhu Okonya1*, Norma Mujica2, Pablo Carhuapoma2 and Jürgen Kroschel2
1)International Potato Center (CIP), P.O. Box 22274, Kampala, Uganda,
2)International Potato Center (CIP), P.O. Box 1558, Lima 12, Peru.
*Email: , Registrant ID# 4601
Cylaspuncticollis (Coleoptera: Brentidae) is the most important insect pest of sweetpotatoin Africa. Root yield losses due to its damage especially during prolonged dry seasons have increased in recent years and do reach 100% in warm lowland areas. C. puncticollis also feeds on sweetpotato leaves and stems reducing vine quality. It has also been reported as a pest of many horticultural and agricultural crops including cotton. We hypothesised that increased temperatures due to global warming will increase the spread and damage potential of C. puncticollis. We developed and validated a temperature-based phenology model for C. puncticollis using the Insect Life Cycle Modeling (ILYCM) software. Through stochastic simulation life-table parameters were estimated. Three risk indices (establishment risk index, ERI; generation index, GI; and activity index, AI) were developed using the C. puncticollis phenology model in ILYCM. The three indices were applied in GIS to map C. puncticollis potential establishment, abundance and spread. Interpolated WorldClim data and downscaled data of the SRES-A1B scenario were applied for current (year 2000) and for future (year 2050) temperature conditions, respectively. C. puncticollis is established in 24 tropical African countries. An ERI>0.95 predicted by the model under the current climatic conditions compare well to its current distribution. Globally, regions with an ERI>0.95 are considered to be at high risk of C. puncticollis permanent establishment. These are sweetpotato growing regions in the tropics and include countries of South America (Colombia, and Venezuela), Central America (Panama, and Honduras) and the whole of the Caribbean, South Asia (Southern India, and Sri Lanka) and South-east Asia (Malaysia, Philippines, Indonesia, Papua New Guinea, Southern Cambodia, Southern Vietnam, and southern Myanmar). A slight decrease (<0.05) of its establishment potential is predicted for tropical lowlands under the 2050 climate but which will not significantly affect its spread potential to other sweetpotato producing countries. However, higher temperature will increase the risk of expansion of C. puncticollis to higher altitude areas of Southern and Eastern Africa. The model predicted the development of 4-7 generations per year of C. puncticollis in most of the tropical sweetpotato producing regions for the year 2000. For most tropical regions, an increase of 1–3 generations per year can be potentially expected for the year 2050. An increase in the number of generations per year implies an increase in abundance resulting into higher pest infestations and sweetpotato yield losses.C. puncticollis is increasingly threatening sweetpotato production and hence household food security in Africa. Further, the pest has a high potential to establish in sweetpotato producing countries outside of Africa. Hence, pre-emptive quarantine and phytosanitary measures are needed to minimize the risks of pest introductions. Adaptation plans for effective pest management are required to better manage the pest in already invaded regions of Africa and to support farmers with adequate integrated pest management practices.