Effect of temperature on the biology of sweetpotato weevil, Cylas brunneus (Coleoptera: Brentidae)

Abstract

Cylas brunneus (Fabricuis) (Coleoptera: Brentidae) is one of the most important insect pests of sweetpotato in Africa. Knowledge of temperature–dependent population growth potential is critical for understanding population dynamics and implementing pest control strategies. This study was carried out to determine the effect of temperature on C. brunneus biology, distribution and abundance. Specifically, the study aimed to determine the (i) effect of temperature on the development, mortality and reproduction of C. brunneus and, (ii) on its potential distribution and abundance under current and future temperatures. The influence of temperature on the biology of C. brunneus was investigated under laboratory conditions at eight constant temperatures (15, 17.5, 20, 25, 30, 32, 35, and 40°C), relative humidity of 60-80% and photoperiod of L12:D12 h. Development of all C. brunneus immature stages was possible from 17.5-32°C. Development time decreased with rising temperatures and was shorter at 30°C for all immature stages. The upper threshold of development was 35°C for eggs and 32°C for larvae and pupae while the lower threshold was 17.5°C for all immature stages. Similarly, adult longevity decreased with increasing temperatures. Mortality of all immature stages showed a similar trend being lowest at temperatures of 25°C for all immature stages and highest at 35°C for egg, 17.5°C for larva and 32°C for pupa. Oviposition peaked at 25°C and was lowest at 17.5°C. Life‐table parameters of C. brunneus were estimated by deterministic phenology model using Insect Life cycle Modeling (ILCYM) software. The intrinsic rate of increase (rm) and the finite rate of increase (λ) indicate a population growth between 20°C and 32°C, with peaks between 20°C and 30°C, where 1.06% of the population growth per was estimated. The second module of ILYCM was used to create potential distribution maps of C. brunneus for the year 2000 and 2050. The maps indicated that temperature change as predicted by Intergovernmental Panel on Climate change, may have serious potential consequences on C. brunneus distribution in most Sub-Saharan African countries leading to spread to new areas that previously were not being affected by the pest. In conclusion, this study showed that increase in temperature will have an impact on the biology, distribution and abundance of C. brunneus in most sub-Saharan African countries where this pest remains a potential risk and threat to sweetpotato production.