by CHAPTER ONE
INTRODUCTION
Background of the Study
Yams are monocotyledonous plants belonging to the genus Dioscorea of the family Dioscoreaceae which constitute a multi-species of crops that are important for food, socio-cultural activities and income. Dioscorea species are important food crops in West Africa, and other tropical countries including East Africa, Central Africa, The Carribean, South America, South East Asia and India Yam (Dioscorea spp.) is an important staple crop in West Africa, particularly in Nigeria, which is the world’s largest producer, accounting for over 70% of global production (FAO, 2022). Beyond its role as a food crop, yam contributes significantly to cultural practices, income generation, and food security among farming households. However, yam production faces several constraints, one of the most destructive being the yam moth (Dasyses rugosella and Scrobipalpa spp.), a storage pest that severely damages stored yam tubers. The most important areas for the cultivation and usage of yam stretches from Ivory Coast through Ghana, Nigeria, Togo, Cameroon, Garbon, Central African Republic and the Western part of the Democratic Republic of Congo. According to F.A.O.(2000) these regions produce about 93% of the World’s annual yam production, estimated at 38.5 million metric tons and Nigeria alone accounts for about 26.4 million tons (70%) in the year 2000. There are about 600 species of Dioscorea with more than 10 species cultivated for food and 6 species for pharmaceutical use (Coursey, 2017). Only six species are economically important namely; white yam (Dioscorea rotundata), water yam (Dioscorea alata), aerialyam(Dioscorea bulbifera), yellowyam (Dioscorea cayenensis), trifoliate yam (Dioscorea dumentorum) andChineseyam (Dioscorea esculenta). (Onwueme,1978), Dioscorea rotundata and Dioscorea cayenensis are indigenous to West Africa while Dioscorea alata and Dioscorea esculenta are native of Asia. According to Onwueme (1978) Dioscorea rotundata is the most important specie of yam in West Africa. Besides the cultivated yam species, there are a number of wild types which are also harvested as food (Wilson, 1982).
The yam tuber is the only economical part of the crop, consumed roasted, fried, boiled, pounded or as flour for baking and steaming for swallowing with soup. In addition to its nutritional value, yam has considerable social and cultural significance, especially among the people of South-Eastern Nigeria (Sangoyomi, 2004). According to Coursey (2017) yams are of a very high nutritional value where it is a major source of carbohydrate, minerals, phosphorus, calcium, iron and vitamins such as thiamine, riboflavin and vitamins B and C. Some species of yam have been used medically to treat diseases like Diabetes melitus, to increase coronary flow and prevent high hyperchosteromia.
Yam moth infestation begins during storage when the larvae bore into tubers, creating tunnels and feeding galleries. The damage not only reduces the market and consumption value of the tubers but also facilitates secondary infection by pathogens, leading to rapid spoilage and post-harvest losses (Okonkwo et al., 2021). Post-harvest losses in yam due to pests such as yam moths are estimated at 25–40% in Nigeria, with significant economic implications for farmers and food security (Adewumi et al., 2023).
Traditionally, synthetic insecticides have been used to control storage pests in yam. While effective, these chemicals pose major drawbacks, including high cost, environmental pollution, development of insect resistance, and health hazards to consumers (Yusuf et al., 2022). Growing concerns about food safety, eco-sustainability, and public health have stimulated interest in safer alternatives such as the use of indigenous plant extracts with pesticidal properties. Several indigenous plants, including neem (Azadirachta indica), bitter kola (Garcinia kola), African pepper (Piper guineense), Siam weed (Chromolaena odorata), and moringa (Moringa oleifera), have been identified to contain bioactive compounds such as alkaloids, tannins, terpenoids, and flavonoids that exhibit insecticidal, repellent, and growth-inhibitory effects on storage pests (Eze & Nwankwo, 2020). For instance, neem extracts have been shown to disrupt insect feeding and reproduction, while powders from Piper guineense seeds possess fumigant action against moth larvae (Ajayi & Fadina, 2021).
Statement of the Problem
Yam (Dioscorea spp.) is one of the most important staple crops in Nigeria, both for its role in food security and for its socio-economic value. However, the storage of yam tubers is severely threatened by the yam moth (Dasyses rugosella and related species), whose larvae bore into the tubers, leaving feeding tunnels and causing extensive post-harvest losses. Studies estimate that yam moth infestation accounts for 25–40% losses in stored yam annually in Nigeria, leading to significant reductions in food availability and farmers’ income (Adewumi et al., 2023).
