Survey of sweetpotato weevils (Clyas spp.) and white grub (Phyllophaga spp.) in Malawi

By: Willard Mbewe, Antony Nyirenda, Margaret Chiipanthenga, Kennedy Masamba, Obed Mwenye, Felistus Chipungu,

Abstract

Although sweetpotato (Ipomoea batatas [L.] Lam.) contributes to household income, food, and nutritional security, its production continues to be threatened by a complex of biotic constraints, including insect pests. Sweetpotato weevils (Cylas spp.) and white grub (phyllophaga spp.) are among the most important sweetpotato pests in sub-Saharan Africa. The report presents results of comprehensive sweetpotato field surveys of the African sweetpotato weevils, Cylas puncticollis Boheman and C. brunneus F. infestation and damage as well as infestation of phyllophaga spp. The pests’ surveys were conducted May – July, 2021 with the aim of determining the infestation, occurrence and distribution of Cylas spp. and phyllophaga spp. in Malawi. A total of 187 sweetpotato fields in twelve districts were sampled. Sweetpotato field infestation rates and root yield loss were assessed. Outside weevil damage (OWD) and inside weevil damage (IWD) were all assessed and their intensity of infestation compared. There were significant variations in weevil damage among the sampled districts with Salima having the highest occurrence of OWD (OR = 37.61, P = <0.001). There were also significant differences OWD among sweetpotato varieties. Among improved varieties, Zondeni was the variety that was heavily infested while Mugamba was the least infested variety. Analysis of deviance showed that there were significant differences (x^2 =2180.0, p <0.001) in the way weevil damaged sweetpotato, with OWD being more severe than IWD. The survey has documented continuous threat that Clyas spp. has on sustainable sweetpotato production in Malawi. The information generated is key in determination of pest management strategies in the country.