Management of the yam moth, <i>Dasyses rugosella</i> Stainton, a pest of stored yam tubers (<i>Dioscorea</i> spp.) using plant products

Abstract

Yams are members of the genus Dioscorea, which produce bulbils, tubers or rhizomes that are of economic importance. West Africa accounts for 90-95% of world production, Nigeria being the major producer. In 2004, the total world production of yam was about 47 million metric tonnes (MT), with 96% of this coming from Africa. Nigeria accounts for about 70% of world production. In spite of the great economic importance of this food item, 20-30% (about 9.4-14.1 million tonnes) is lost during storage. Storage losses of the order of 10-15% after the first three months and approaching 50% after six months have been observed. Yam tubers in storage are attacked by several moth and beetle pests. The moth pests include Dasyses rugosella Stainton, Euzopherodes vapidella Mann and Decadarchis minuscula Walsingham. Dioscorea alata L. (water yam) was found to be the most susceptible species of yam to infestation by these moths. The plant powders tested for their efficacy against D. rugosella included Capsicum frutescens L. (fruit), C. annum Miller (fruit), Piper guineense Schum and Thonn (seed), Aframomum melegueta Schum (seed), Allium cepa L. (scale), A. sativum L. (scale), Citrus sinensis Osbeck (peel) and Azadirachta indica A. Juss (leaf). In another experiment, the oil extracts of the following plants were tested against D. rugosella, Jatropha gossypifolia L. (fruits), Arachis hypogaea L. (seeds), Citrus sinensis Osbeck (seeds), Elaeis guineensis Jacq (kernel), Piper guineense Schum and Thonn (seeds), Aframomum melegueta Schum (seeds) and Adansonia digitata L. (fruits). Results showed that powders of C. annum and C. frutescens were effective against the adult moth producing 100% mortality within 24hrs of application of powder. In addition, P. guineense, A. cepa and A. sativum were effective against D. rugosella within 3 days of application of plant powder. However, C. annum and C. frutescens were able to effectively persist for 14days after application of plant powders. There was no fecundity of the moth in sample treated with C. annum and C. frutescens while fecundity was reduced in others. The survival of the moth from eggs to adults when treated with the plant powders showed that there was significantly (PArachis hypogaea and E. guineensis were effective in preventing adult emergence. This study showed that some plant products (powders of C. annum and C. frutescens and oils of A. hypogaea, P. guineense and E. guineensis) were toxic or very effective against the yam moth, D. rugosellaand the powders can be applied on cut or damaged surfaces of yam tubers to prevent hatching of the eggs of the moth there by helping in their management and also minimize rotting.

Keywords: Toxicity, Dasyses rugosella, Management, Mortality, Powder extract