Response of chips and flour from four yam varieties to Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) infestation in storage

Chips and flour from four different yam varieties (Ame, Adaka, Nwopoko and Obiaturugo) obtained from the National Root Crops Research Institute (NRCRI), Umudike, Abia State, Nigeria were evaluated for responses to Tribolium castaneum (rust-red flour beetle) infestation in the laboratory under prevailing conditions (25-30°C and 70-90 RH) for a period of 90 days. 10 g of either chips or flour of each of the yam varieties were infested with 8 pairs of adult T. castaneum in 200 ml air-tight plastic containers. The experiment was set up in a completely randomized design (CRD) and experiments were replicated three times. The result showed that both forms of yam varieties were susceptible to T. castaneum but to varying degrees. The variation of susceptibility observed across the treatments showed that Nwopoko chips were the most susceptible and Nwopoko flour was the least susceptible. Development of T. castaneum was prolonged on flour than on the chips. Percentage weight loss was highest (3.33) in Adaka flour and weight gain was highest (3.67) in Nwopoko chips. The result also showed variations in the physicochemical and functional properties of the different yam varieties which played a role in pest performance and preference. T. castaneum has proved to be a cosmopolitan species that is able to colonize a wide range of substrates including different forms and types of yam cultivated in the Niger delta region of Nigeria. The outcome of this study necessitates the introduction of precautionary measures against this pest in order to prevent it from attaining pest status and causing economic damage to these yam products in storage.   Key words: Tribolium castaneum, yam, chips, flour, susceptibility index.